Cross Reference to Related Applications
Background of the Invention
1. Field of the Invention
[0002] The disclosure generally relates to a noise cancellation technology, more particularly,
to an active noise cancellation integrated circuit for stacking at least one anti-noise
signal and at least one non-anti-noise signal, an associated method, and an active
noise cancellation headphone using the same.
2. Description of the Prior Art
[0003] General noise reduction techniques for headphones include passive noise cancellation
(PNC) and active noise cancellation (ANC). The passive noise cancellation mainly isolate
noise as much as possible through headphone sound-insulation materials or special
structures, which generally are in-ear headphones or over-ear headphones. Wearing
these two-types headphones for a long period of time cause ear pain, and excessive
sound pressure may even cause users' hearing loss. The active noise cancellation means
that a special noise cancellation circuit is set in headphones. Generally, an audio
receiver (such as a miniature microphone) and an anti-noise output chip are used to
receive and analyze frequency of external noise and generate an anti-noise sound in
inverted phase. By the destructive interference, the external noise would be canceled.
[0004] Further, the active noise cancellation (ANC) generally includes feed-forward ANC,
feedback ANC and hybrid ANC. Regarding the feed-forward ANC, a noise receiving microphone
is disposed outside of headphones for receiving noise outside the headphone, and an
anti-noise signal is generated by a digital signal processing integrated circuit.
Regarding the feedback ANC, a noise receiving microphone is disposed inside headphones
for receiving audio in ear canals, and an anti-noise signal is generated by feedback
the audio to the digital signal processing integrated circuit. In addition, the hybrid
ANC uses two or more noise receiving microphones to pick up noises, and generates
multiple anti-noise signals through different digital signal processing integrated
circuits, respectively, and stacks the anti-noise signals to eliminate noises.
Summary of the Invention
[0005] Since audio waves are generated by signals from multiple microphones disposed on
different positions and by different signal process, an end observation point receives
the superposition of multiple audio waves, which leads to undesired compensation such
that a user may hear degraded audio playback. In view of this, how to reduce or eliminate
the above-mentioned deficiencies in related field is a problem to be solved. An active
noise cancellation integrated circuit, an active noise cancellation method, and an
active noise cancellation headphone according to the invention are defined in the
independent claims. The dependent claims define preferred embodiments thereof.
[0006] The present invention provides an active noise cancellation headphone, the active
noise cancellation headphone includes an audio-to-electrical signal conversion device
and an active noise cancellation integrated circuit for stacking at least one anti-noise
signal and at least one non-anti-noise signal of the present invention. The active
noise cancellation integrated circuit for stacking at least one anti-noise signal
and at least one non-anti-noise signal includes a first path, a second path and a
first decoupling unit, wherein the first path outputs a first path non-anti-noise
signal, wherein the first path non-anti-noise signal is converted to a first signal
by a physical channel, wherein the first path includes a non-ANC filtering unit for
generating a non-anti-noise signal, wherein the second path receives the error signal
which includes a component of the first signal, and outputs a second path anti-noise
signal to the physical channel, wherein the second path includes an ANC filtering
unit for generating an anti-noise signal, wherein the second path anti-noise signal
is derived from the anti-noise signal. The first decoupling unit is for removing the
component of the first signal from the second path based on the non-anti-noise signal.
[0007] The present invention further provides an active noise cancellation (ANC) method
for stacking at least one anti-noise signal and at least one non-anti-noise signal,
adapted for an audio playback device with at least one ANC filter and at least one
non-ANC filter. The active noise cancellation method for stacking at least one anti-noise
signal and at least one non-anti-noise signal includes: providing a first path outputting
a first path non-anti-noise signal, wherein the first path non-anti-noise signal is
converted to a first signal by a physical channel, wherein the first path includes
a non-ANC filtering unit, for generating a non-anti-noise signal; providing a second
path receiving an error signal including a component of the first signal, and outputting
a second path anti-noise signal to the physical channel, wherein the second path includes
an ANC filtering unit for generating an anti-noise signal, wherein the second path
anti-noise signal is derived from the anti-noise signal; removing the component of
the first signal from the second path based on the non-anti-noise signal; and performing
playback based on the first path non-anti-noise signal and the second path anti-noise
signal to eliminate noise.
[0008] The spirit or gist of the present invention is to set at least one ANC filtering
unit and at least one non-ANC filtering unit in the active noise cancellation apparatus
of the active noise cancellation headphone. Moreover, the redundant component(s) generated
from the output signal of the active noise cancellation filtering unit is/are canceled
by the decoupling method. Thus, with the help of the proposed decoupling technique,
the intended purpose of the non-ANC filter, such as hearing aid, pass-through, or
personal sound amplification, can be achieved by mitigating or suppressing the side
effect caused by the ANC filter.
[0009] The other advantages of the present invention will be explained in more detail in
conjunction with the following description and drawings.
[0010] Both the foregoing general description and the following detailed description are
examples and explanatory only, and are not restrictive of the invention as claimed.
[0011] These and other objectives of the present invention will no doubt become obvious
to those of ordinary skill in the art after reading the following detailed description
of the preferred embodiment that is illustrated in the various figures and drawings.
Brief Description of the Drawings
[0012]
FIG. 1 illustrates a diagram depicting active noise cancellation headphones according
to a preferred embodiment of the present invention.
FIG. 2 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone according to a preferred embodiment of the present invention.
FIG. 3 illustrates a diagram depicting comparison of results of noise cancellation
in FIG. 2.
FIG. 4 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between the ear canal and environment
according to a preferred embodiment of the present invention.
FIG. 5 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between the ear canal and environment
according to a preferred embodiment of the present invention.
FIG. 6 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between the ear canal and environment
according to a preferred embodiment of the present invention.
FIG. 7 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone without good isolation between the ear canal and environment
according to a preferred embodiment of the present invention.
FIG. 8 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone according to a preferred embodiment of the present invention.
FIG. 9 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between the ear canal and environment
according to a preferred embodiment of the present invention.
FIG. 10 illustrates a flowchart depicting an active noise cancellation method for
stacking multiple anti-noise signals according to a preferred embodiment of the present
invention.
FIG. 11 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention.
FIG. 12 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention.
FIG. 13 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention.
FIG. 14 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone without good isolation between an ear canal and environment
according to a preferred embodiment of the present invention.
FIG. 15 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between the ear canal and environment
according to a preferred embodiment of the present invention.
FIG. 16 illustrates a flowchart depicting an active noise cancellation method for
stacking at least one anti-noise signal and at least one non-anti-noise signal according
to a preferred embodiment of the present invention.
FIG. 17 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone between the ear canal and environment according to a
preferred embodiment of the present invention.
Detailed Description
[0013] Reference is made in detail to embodiments of the invention, which are illustrated
in the accompanying drawings. The same reference numbers may be used throughout the
drawings to refer to the same or like parts, components, or operations.
[0014] The present invention will be described with respect to particular embodiments and
with reference to certain drawings, but the invention is not limited thereto and is
only limited by the claims. It will be further understood that the terms "comprises,"
"comprising," "includes" and/or "including," when used herein, specify the presence
of stated features, integers, steps, operations, components, and/or components, but
do not preclude the presence or addition of one or more other features, integers,
steps, operations, components, components, and/or groups thereof.
[0015] Use of ordinal terms such as "first", "second", "third", etc., in the claims to modify
a claim component does not by itself connote any priority, precedence, or order of
one claim component over another or the temporal order in which acts of a method are
performed, but are used merely as labels to distinguish one claim component having
a certain name from another component having the same name (but for use of the ordinal
term) to distinguish the claim components.
[0016] It will be understood that when a component is referred to as being "connected" or
"coupled" to another component, it can be directly connected or coupled to the other
component or intervening components may be present. In contrast, when a component
is referred to as being "directly connected" or "directly coupled" to another component,
there are no intervening components present. Other words used to describe the relationship
between components should be interpreted in a like fashion (e.g., "between" versus
"directly between," "adjacent" versus "directly adjacent." etc.)
[0017] FIG. 1 illustrates a diagram depicting active noise cancellation headphones according
to a preferred embodiment of the present invention. Referring to FIG. 1, in this embodiment,
wireless headphones are served as an example. The wireless headphones are a pair of
devices with wireless communication function, which includes a left wireless earbud
101 and a right wireless earbud 102. There is no physical wire connecting between
the left wireless earbud 101 and the right wireless earbud 102. A wireless communication
protocol, such as A2DP (advanced audio distribution profile) Bluetooth package, can
be used to transmit the user's speech signal or music package between the mobile device
103 and the left wireless earbud 101 and between the mobile device 103 and the right
wireless earbud 102.
[0018] In other embodiments, other peer-to-peer methods such as Wi-Fi Direct, can also be
used between the mobile device 103 and the left wireless earbud 101 and between the
mobile device 103 and the right wireless earbud 102, the present invention is not
limited thereto.
[0019] In the abovementioned embodiment, although wireless headphones are taken as an example
of active noise cancellation headphones, people having ordinary skill in the art should
know that active noise cancellation headphones may also be wired headphones, and the
present invention is not limited thereto.
[0020] FIG. 2 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone according to a preferred embodiment of the present invention.
Referring to FIG. 2, in this embodiment, the active noise cancellation headphone takes
in-ear headphones as an example. The active noise cancellation headphone includes
the active noise cancellation integrated circuit 20 and the audio-to-electrical signal
conversion device 21. The audio-to-electrical signal conversion device 21 in this
embodiment includes a first microphone 201, a second microphone 202 and a speaker
(not shown). In the embodiment of the present invention, for the purpose of illustrating
the spirit or gist of the present invention, a dashed outer frame is used as an example
for illustration, and the inside of the dashed outer frame indicates the inside of
a headphone shell 19. The first microphone 201 is on the outside of the dashed outer
frame, it means that the first microphone 201 is disposed outside an ear canal to
receive noise outside the ear canal. The second microphone 202 is inside the dashed
outer frame, it means that the second microphone 202 is disposed in the ear canal.
In the following embodiments, the dashed outer frame is used as an illustration. However,
the dashed outer frame cannot be utilized for limiting the configuration of the components
of the present invention.
[0021] The first microphone 201 is disposed outside the headphone shell 19, and is mainly
used for receiving an external noise signal of the in-ear headphone. The external
noise signal captured by the first microphone 201 is, for example, to be sampled and
applied with analog-to-digital conversion. After that, the external noise signal is
converted into an electrical signal and the electrical signal is input to the active
noise cancellation integrated circuit 20. The first microphone 201 may be referred
to as the reference microphone.
[0022] The second microphone 202 is disposed inside the headphone shell 19 and is located
between the headphone shell 19 and an eardrum, and is mainly used to receive noises
and echoes in a user's ear canal, that is, the ear canal echo. The headphone shell
19 is used to provide passive noise cancellation. For example, the headphone shell
19 includes material of sound insulation component. More specifically, the second
microphone 202 is used to receive an audio signal in user's ear canal. The audio signal
captured by the second microphone 202 would be converted into an electrical signal
which is input to a second ANC filtering unit 204. The second microphone 202 may be
served as an error microphone.
[0023] The active noise cancellation integrated circuit 20 is used for generating an anti-noise
electrical signal based on the electrical signal obtained by the first microphone
201 and the electrical signal obtained by the second microphone 202. For example,
the anti-noise electrical signal in digital form is converted into an anti-noise audio
signal sequentially through a digital-to-analog converter (DAC), a reconstruction
filter, a power amplifier and a speaker. For analysis, the aforementioned conversion
would be represented as a transfer function. In brief, the anti-noise electrical signal
is converted into the anti-noise audio signal in audio form through the transfer function
according to the aforementioned transmission. Accordingly, in order to evaluate the
transfer function of the aforementioned transmission, it is necessary to involve the
anti-noise electrical signal and the anti-noise audio signal into analysis.
[0024] However, the anti-noise audio signal in audio form cannot be directly obtained in
practice. A possible alternative is to receive the anti-noise audio signal through
the second microphone 202 in the absence of an external noise signal, and to convert
the anti-noise audio signal into another analog electrical signal in analog form.
The analog electrical signal is further converted into an electrical signal in digital
form, for example, sequentially through a preamplifier, an anti-aliasing filter and
an analog-to-digital converter, wherein the said electrical signal in digital form
is used to replace the anti-noise audio signal in audio form to evaluate the transfer
function.
[0025] Although the transfer function obtained in the alternative way involves not only
the transmission path from the active noise cancellation integrated circuit 20 to
an input of the second microphone 202 but also the transmission path from an output
of the second microphone 202 to the active noise cancellation integrated circuit 20.
However, in order to simplify the analysis, the transfer function can be used to represent
the transmission path from the active noise cancellation integrated circuit 20 to
the input of the second microphone 202, wherein the transfer function is here served
as a physical channel 205. It should be noted that the physical channel 205 includes
the aforementioned speaker. In brief, the anti-noise electrical signal output by the
active noise cancellation integrated circuit 20 is converted into an anti-noise audio
signal in audio form through the aforementioned physical channel 205.
[0026] In addition, an another transmission path where the external noise signal enters
the inner side of the headphone shell 19 from the outer side of the headphone shell
19 to a final arrival of the second microphone 202 is the primary path (not shown)
. For analysis, the primary path is presented as a transfer function. In brief, the
external noise signal is converted into a residual noise signal by the transfer function
of the primary path. Accordingly, to evaluate the transfer function of the primary
path, it is necessary to involve the external noise signal and the residual noise
signal into analysis.
[0027] However, in practice, the external noise signal and the residual noise signal cannot
be directly obtained. A possible alternative is to receive the external noise signal
through the first microphone 201 and to convert the external noise signal into another
electrical signal in analog form. The another electrical signal in analog form is
converted to an electrical signal in digital form, for example, sequentially through
a preamplifier, an anti-aliasing filter and an analog-to-digital converter, wherein
the said electrical signal in digital form is used to replace the external noise signal
to evaluate the transfer function of the primary path. On the other hand, the residual
noise signal is received through the second microphone 202 under a circumstance that
the active noise cancellation integrated circuit 20 is disabled, and the residual
noise signal is converted into the other electrical signal in an analog form. The
other electrical signal in an analog form is converted to another electrical signal
in digital form, for example, sequentially through a preamplifier, an anti-aliasing
filter and an analog-to-digital converter, wherein the said another electrical signal
in digital form is used to replace the residual noise signal to evaluate the transfer
function of the primary path.
[0028] During actual operation of the active noise cancellation headphone (that is, when
the active noise cancellation integrated circuit 20 is enabled), the anti-noise signal
interferes with the residual noise signal to achieve the effect of active noise cancellation.
[0029] The active noise cancellation integrated circuit 20 includes a first path and a second
path.
[0030] The first path receives an output signal from the first microphone 201, and outputs
a first path anti-noise signal to the physical channel 205. The first path anti-noise
signal is converted to a first signal for noise cancellation by the physical channel
205.
[0031] The second path receives an output signal from the second microphone 202, and outputs
a second path anti-noise signal to the physical channel 205. The second path anti-noise
signal is converted to a second signal for noise cancellation by the physical channel
205.
[0032] The first path includes a first ANC filtering unit 203. Further, the first path is
from an output terminal of the first microphone 201, via the first ANC filtering unit
203, to an input terminal of the physical channel 205.
[0033] The second path includes a second ANC filtering unit 204. Further, the second path
is from an output terminal of the second microphone 202, and via the second ANC filtering
unit 204, to an input terminal of the physical channel 205.
[0034] In the embodiment of FIG. 2, the first ANC filtering unit 203 performs filtering
process on an electrical signal output by the first microphone 201 to generate a first
anti-noise signal y'
1(n). The first anti-noise signal y'
1(n) is served as the first path anti-noise signal in this embodiment. A weighting
of the first ANC filtering unit 203 is labeled as W
1 in FIG. 2. The first ANC filtering unit 203 can be implemented by a variety of means,
such as general purpose hardware (e.g., a microcontroller, a digital signal processor,
a single-core processor, a multi-core processor with capability of parallel processing,
a graphic processor, or other processor with the computational capability), to provide
active noise cancellation filtering operation when software and/or firmware instructions
are performed.
[0035] The second ANC filtering unit 204 performs filtering process on the output electrical
signal of the second microphone 202 to generate a second anti-noise signal
y'
2(
n). The second anti-noise signal
y'
2(
n) in this embodiment is served as the second path anti-noise signal. A weighting of
the second ANC filtering unit 204 is labeled as
W2 in FIG. 2. The second ANC filtering unit 204 can be implemented by a variety of means,
such as general purpose hardware (e.g., a microcontroller, a digital signal processor,
a single-core processor, a multi-core processor with capability of parallel processing,
a graphic processor, or other processor with the computational capability), to provide
active noise cancellation filtering operation when software and/or firmware instructions
are performed.
[0036] In this embodiment, the first anti-noise signal
y'
1(
n) and the second anti-noise signal
y'
2(
n) are individually input to the physical channel 205. However, the present invention
is not limited thereto. In some embodiment, the first anti-noise signal
y'1(
n) and the second anti-noise signal
y'2(
n) may be added together in digital domain, then the added anti-noise signal is input
to the physical channel 205.
[0037] In the audio-to-electrical signal conversion device 21,the first anti-noise signal
y'
1(
n) and the second anti-noise signal
y'
2(
n) are converted to an audio signal through the physical channel 205 to synthesize
a noise cancellation signal, that is, the aforementioned anti-noise signal. Due to
the reflection and attenuation of sound waves in the ear canal, echo interference
occurs when the noise cancellation signal is actually conducted in the ear canal.
In other words, the noise cancellation signal would reach user's ear and the second
microphone 202 through a real environment physical channel.
[0038] In this embodiment, the active noise cancellation integrated circuit 20 for stacking
multiple anti-noise signals is, for example, a dual anti-noise system with two active
noise cancellation filter units 203 and 204 that can output two noise cancellation
signals correspondingly. In general, the two noise cancellation signals are expected
to interfere with each other, thereby reaching the effect of suppressing noise. However,
the above expectation is unlikely to happen in reality, and the detailed descriptions
are as follow in FIG. 3. Referring to FIG. 3, FIG. 3 is a schematic diagram depicting
comparison of noise cancellation results of FIG. 2 of this embodiment.
[0039] As shown in FIG. 3, a vertical axis represents a magnitude of amplitude and a horizontal
axis represents frequency. The label 301 represents a noise signal; the label 302
represents the noise suppression result when only the first ANC filtering unit 203
(i.e. feedforward filter, FF) is enabled; the label 303 represents the noise suppression
result when only the second ANC filtering unit 204 (i.e. feedback filter, FB) is enabled;
the label 304 represents the expected noise suppression result when the first ANC
filtering unit 203 and the second ANC filtering unit 204 (FF+FB) are both enabled;
and the label 305 represents the real noise suppression result when the first ANC
filtering unit 203 and the second ANC filtering unit 204 (FF+FB) are both enabled.
Comparing labels 304 and 305, it can be observed that labels 304 and 305 overlap in
relatively lower band, but not at relatively high frequencies. That is to say, in
relatively high band, the actual noise suppression result cannot reach the expected
noise suppression result.
[0040] The reason why the unexpected noise suppression result occurs will be explain, please
return to FIG. 2. The symbol d(n) represents a primary noise signal originating from
the external noise signal, that is, the aforementioned residual noise signal; the
symbol
y1(
n) represents the first signal related to the first anti-noise signal
y'
1(
n) output by the first ANC filtering unit 203, the first signal
y1(
n) is the audio signal; the symbol
y2(
n) represents the second signal related to the second anti-noise signal
y'
2(
n) output by the second ANC filtering unit 204, and the second signal
y2(
n) is the audio signal; and the symbol
e(
n) represents an error signal output by the second microphone 202. It should be noted
that, in order to simplify the description, the process of converting the audio signal
into an electrical signal in digital form is omitted.
[0041] The error signal
e(
n) output by the second microphone 202 can be regarded as an electrical signal in digital
form.
[0042] When none of the active noise cancellation filtering units 203 and 204 is turned
on, the second microphone 202 would only capture the primary noise signal d(n) as
the error signal e(n), that is,
e(
n) =
d(
n). When the second ANC filtering unit 204 is turned on, the second microphone 202
would capture the primary noise signal
d(
n) and the second signal y
2(n) to serve as the error signal
e(
n), that is,
e(
n)=
d(
n)+
y2(
n)
. The primary noise signal
d(
n) and the second signal
y2(
n) are added by an adding unit 206. It should be noted that the adding unit 206 shown
in the FIG. 2 is not a physical component, and is only used to facilitate interpretation
and analysis. Similarly, when the active noise cancellation filtering units 203 and
204 are turned on, the second microphone 202 would capture the primary noise signal
d(
n), the first signal
y1(
n) and the second signal
y2(
n) to serve as the error signal
e(
n), that is,
e(
n) =
d(
n)+
y1(
n)+
y2(
n)
.
[0043] The second ANC filtering unit 204 generates the second anti-noise signal
y'
2(
n) based on the error signal
e(
n) received by the second microphone 202. However, in this circumstance, based on the
formula
e(
n)=
d(
n)+
y1(
n)+
y2(
n), the error signal
e(
n) captured by the second microphone 202 is interfered by the first signal
y1(
n), such that the second anti-noise signal
y'
2(
n) generated by the second ANC filtering unit 204 is not effective, which causes issues
such as excessively processing noise. In brief, due to all of audio received by the
second microphone 202 including the first signal
y1(
n)
, actual noise wouldn't be properly suppressed or would be overcompensated.
[0044] The headphone type in the above embodiment is an in-ear headphone . That is to say,
the headphone shell 19 is considered to effectively block the second signal
y2(
n) from propagating to the outside of the in-ear headphone, so that the first microphone
201 cannot receive the second signal
y2(
n).
[0045] If the headphone type is an open-type headphone, the headphone shell 19 would be
considered that the second signal
y2(
n) cannot be effectively blocked from propagating to the outside of the headphone,
and the first microphone 201 would receive the second signal
y2(
n). That would cause more serious mutual interference, and it would cause more severe
noise even than the noise under only single noise cancellation being turned on in
the system.
[0046] In order to address the above issue, a possible way is to remove the component of
the first signal
y1(
n) from the error signal
e(
n) based on the mathematical principle of linear system, as shown in the embodiment
of FIG. 4.
[0047] FIG. 4 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention. The active noise cancellation
headphone in FIG. 4 adopts hybrid noise cancellation architecture. Referring to FIG.
4, the active noise cancellation headphone in FIG. 4 is similar to the active noise
cancellation headphone in FIG. 2, and the difference is that the active noise cancellation
integrated circuit 20 for stacking multiple anti-noise signals in FIG. 4 further includes
a first decoupling unit 40. The first decoupling unit 40 is used to remove the first
signal
y1(
n) from the error signal e(n) captured by the second microphone 202 by electrical signal
processing. In some embodiments, the first decoupling unit 40 may be implemented by
a digital signal processor. In this embodiment, the first path is from an output terminal
of the first microphone 201, via the first ANC filtering unit 203, to an input terminal
of the physical channel 205; and the second path is from an output terminal of the
second microphone 202, via the second ANC filtering unit 204, to an input terminal
of physical channel 205.
[0048] The first decoupling unit 40 includes a first channel simulation filter 401 and a
first adder circuit 402. The first channel simulation filter 401 simulates, for example,
a transfer function of the physical channel 205. The simulated physical channel is
represented as the Z-domain transfer function
Ŝ(
z)
. In other words, the simulated physical channel
Ŝ(
z) is substantially equivalent to the physical channel
S(
z) 205.
[0049] The physical channel 205 is used to represent transmission from an filter (e.g. the
first ANC filtering unit 203 or the second ANC filtering unit 204) to the second microphone
202, in order to analyze the transformation of an electrical signal output by the
ANC filter after the transmission, wherein the transfer function
S(
z) represents the simulation result. In some possible implementations, the external
noise source is removed, and the transfer function
S(
z) is evaluated based on the electrical signal output by the ANC filter and the error
signal e(n) acquired from the second microphone 202, wherein there is no primary noise
signal
d(
n) since the external noise source is removed. Thus, the error signal is substantially
equivalent to at least one of the first signal
y1(
n) and the second signal
y2(
n) or the sum of the first signal
y1(
n) and the second signal
y2(
n) according to the enablement state of the first ANC filtering unit 203 and the second
ANC filtering unit 204.
[0050] The first channel simulation filter 401 receives the first anti-noise signal
y'
1(
n) output by the first ANC filtering unit 203 to generate the first decoupling signal
ŷ1(
n). In this case where the simulated physical channel
Ŝ(
z) is substantially the same as the physical channel
S(
z) 205, since an input signal of the simulated physical channel
Ŝ(
z) and an input signal of the physical channel
S(
z) 205 are both first anti-noise signal
y'
1(
n), the first decoupling signal
ŷ1(
n) output by the simulated physical channel
Ŝ(
z) is substantially equivalent to the first signal
y1(
n) output by the physical channel
S(
z) 205. Next, a first input port of the first adder circuit 402 receives the first
decoupling signal
ŷ1(
n), and a second input port of the first adder circuit 402 receives the error signal
e(
n). Then, the first adder circuit 402 deducts the component of the first decoupling
signal
ŷ1(
n) from the error signal
e(
n), which can be deemed as deducting the first signal
y1(
n) from the error signal
e(
n), and provides the deducted result to the second ANC filtering unit 204. The error
signal
e(
n) received by the second ANC filtering unit 204 is substantially equal to
d(
n)+
y2(
n) and no longer contains the first signal
y1(
n)
. Therefore, the noise suppression effect would be significantly improved. In this
embodiment, the first decoupling unit 40 deducts the first signal
y1(
n) from the error signal
e(
n) by electrical signal process, so as to solve the abovementioned issue of overcompensation.
[0051] FIG. 5 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention. In FIG. 5, the active
noise cancellation headphone adopts hybrid active noise cancellation architecture.
Referring to FIG. 2 and FIG. 5, in this embodiment, a first decoupling unit 50 is
also extra added to the active noise cancellation integrated circuit 20 for stacking
multiple anti-noise signals to remove the first signal
y1(
n) by electrical signal process.
[0052] In this embodiment, the first decoupling unit 50 includes a first channel simulation
filter 501, a third ANC filtering unit 502, a first adder circuit 503 and a second
adder circuit 504.
[0053] Function of the first channel simulation filter 501 is the same as that of the first
channel simulation filter 401 in the embodiment of FIG. 4. The first channel simulation
filter 501 is used to simulate the physical channel 205, and receive the first anti-noise
signal
y'
1(
n) to generate the first decoupling signal
ŷ1(
n), wherein the first anti-noise signal
y'
1(
n) is obtained in a manner in which the external noise signal is received by the first
microphone 201, in turn applied with sampling and analog-to-digital conversion, and
further in turn processed by the first ANC filtering unit 203.
[0054] In this embodiment, the transfer function of the third ANC filtering unit 502 is,
for example, the same as the transfer function of the second ANC filtering unit 204.
Therefore, the weighting of the third ANC filtering unit 502 is also
W2. That is to say, the filtering operation of the third ANC filtering unit 502 is the
same as that of the second ANC filtering unit 204. Thus, when the first decoupling
signal
ŷ1(
n) is input to the third ANC filtering unit 502, the third anti-noise signal output
by the third ANC filtering unit 502 can be represented as
ŷ1(
n)
W2.
[0055] The second ANC filtering unit 204 receives the error signal output by the second
microphone 202, which is marked as
d(
n)+
y1(
n)+y
2(
n)
, so the signal output by the second ANC filtering unit 204 is marked as [
d(
n)+
y1(
n)+
y2(
n)]
W2.
[0056] A first input port of the first adder circuit 503 receives the third anti-noise signal
ŷ1(
n)
W2, and a second input port of the first adder circuit 503 receives the second anti-noise
signal [
d(
n)+
y1(
n)+
y2(
n)]
W2. Since
ŷ1(
n) is substantially equivalent to
y1(
n), after one of the two signals is subtracted from the other of the two signals by
the first adder circuit 503, an output of the first adder circuit 503 is approximately
equal to [
d(
n)+
y2(
n)]
W2. Further, the primary noise signal d(n) in the output [
d(
n)+
y2(
n)]
W2 is negligible. Therefore, the output [
d(
n)+
y2(
n)]
W2 can be further simplified to the formula [
y2(
n)]
W2, which is represented here as
y'
2(
n). It can be seen that although the second ANC filtering unit 204 is interfered by
the first signal
y1(
n), the interference is equivalently eliminated by the third ANC filtering unit 502
and the first adder circuit 503.
[0057] A first input port of the second adder circuit 504 is coupled to an output port of
the first adder circuit 503 to receive the output
y'2(
n), and a second input port of the second adder circuit 504 receives the first anti-noise
signal
y'
1(
n). One of the two signals is added the other of the two signals to obtain
y'1(
n)+y
'2(
n), which is served as the component of the electrical signal of the noise cancellation
signal. In another preferred embodiment, the second adder circuit 504 may be omitted.
[0058] The abovementioned embodiment in FIG. 5 adopts a different decoupling method from
that in FIG. 4, but it can also eliminate the component of the redundant first signal
y1(
n)
. Another embodiment is proposed below, which can also eliminate the component of the
redundant first signal
y1(
n), such that people having ordinary skill in the art can implement the present invention
accordingly.
[0059] FIG. 6 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention. In FIG. 6, the active
noise cancellation headphone also adopts hybrid active noise cancellation architecture.
Different from the embodiment in FIG 5, the error signal
e(
n) provided by the second microphone 202 is processed to achieve the effect of decoupling.
In the embodiment in FIG. 6, a signal provided by the first microphone 201 is processed
to achieve the effect of decoupling. The detail description is as follows.
[0060] The first decoupling unit 60 includes a third ANC filtering unit 601, a channel simulation
filter 602, a first adder circuit 603 and a second adder circuit 604, wherein the
function of the channel simulation filter 602 is the same as the function of the first
channel simulation filter 401 in the embodiment of FIG. 4.
[0061] The operation of the third ANC filtering unit 601 is the same as the operation of
the second ANC filtering unit 204. The difference is that the third ANC filtering
unit 601 receives the first anti-noise signal
y'
1(
n) output by the first ANC filtering unit 203, and outputs the third anti-noise signal
y'
1(
n)
W2. Afterward, the third anti-noise signal
y'
1(
n)
W2is processed by the first channel simulation filter 602 to generate the first decoupling
signal
ŷ1(
n)
W2.
[0062] Furthermore, the operation of the third ANC filtering unit 601 is similar to that
of the third ANC filtering unit 502 in FIG. 5. The difference is that the first anti-noise
signal
y'
1(
n) in the embodiment of FIG. 5 is first processed by the first channel simulation filter
501 processed, and then processed by the third ANC filtering unit 502. In this embodiment,
the first anti-noise signal
y'
1(
n) is first processed by the third ANC filtering unit 601 and then processed by the
channel simulation filter 602. According to the mathematical principle of the linear
system, the abovementioned difference in the configuration sequence does not substantially
lead to the change of the result. The detail description is omitted. Accordingly,
in some embodiments, the first anti-noise signal
y'
1(
n) can be configured to be processed by the channel simulation filter 602 first, and
then in turn processed by the third ANC filtering unit 601.
[0063] A first input port of the first adder circuit 603 receives the first decoupling signal
ŷ1(
n)
W2, a second input port of the first adder circuit 603 receives the first anti-noise
signal
y'
1(
n), and one of the two signals is subtracted from the other of the two signals. Then,
the subtracted signal and a signal on the path of the second ANC filtering unit 204
are interfered with each other through the second adder circuit 604 to eliminate the
component of the first signal
y1(
n) from the anti-noise signal [
d(
n)+
y1(
n)+
y2(
n)]
W2 output by the second ANC filtering unit 204. Specifically, the component
ŷ1(
n)
W2 in the signal [
y'1(
n)
-ŷ1(
n)
W2] output by the first adder circuit 603 is used to cancel the component [
y1(
n)
W2] in the anti-noise signal [
d(
n)+
y1(
n)+
y2(
n)]
W2 output by the second ANC filtering unit 204. Moreover, the primary noise signal d(n)
in the anti-noise signal [
d(
n)+
y2(
n)+
y2(
n)]
W2 can be ignored. Accordingly, the signal output by the second adder circuit 604 is
[
y2(
n)
W2+
y'1(
n)]
, which can be further simplified as [
y'2(
n)+
y'1(
n)]
.
[0064] In the abovementioned embodiments, in-ear headphone is taken as an example. Since
the in-ear headphone has a good isolation effect between the internal microphone and
the external microphone, the noise received by the internal microphone cannot be received
by the external microphone. Therefore, in the abovementioned embodiments, echo noise
cannot affect the first microphone 201. The following embodiment is an example without
have good isolation.
[0065] FIG. 7 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone without good isolation between an ear canal and environment
according to a preferred embodiment of the present invention. In FIG. 7, the active
noise cancellation headphone also adopts hybrid active noise cancellation architecture.
Referring to FIG. 7, in this embodiment, the active noise cancellation headphone is
semi-in-ear headphone. Since a headphone shell 19 of this type of active noise cancellation
headphone cannot effectively block sound passing from the inside of the active noise
cancellation headphone to the outside of the active noise cancellation headphone,
the first microphone 201 disposed outside of the headphone would be interfered by
the echo noise inside the ear canal. Therefore, in addition to the first decoupling
unit 40, the active noise cancellation device of the above-mentioned active noise
cancellation headphone system further includes a second decoupling unit 70.
[0066] This embodiment has the same concept as the abovementioned several embodiments. The
first decoupling unit 40 is used for generating a first decoupling signal according
to an anti-noise signal output by the first ANC filtering unit 203. Similarly, the
second decoupling unit 70 is used for generating a second decoupling signal according
to an anti-noise signal output by the second ANC filtering unit 204.
[0067] Similar to the embodiment in FIG. 4, in this embodiment, the first decoupling unit
40 includes a first channel simulation filter 401 and a first adder circuit 402. The
first channel simulation filter 401, substantially equal to the physical channel 205,
receives the first anti-noise signal y'
1(n) output by the first ANC filtering unit 203 to generate the first decoupling signal
ŷ1(
n)
. The first decoupling signal
ŷ1(
n) is substantially equal to the first signal
ŷ1(
n). The first error signal
e2(
n) received by the second microphone 202 is [
d2(
n)+
y1(
n)+
y2(
n)]. Next, a first input port of the first adder circuit 402 receives the first decoupling
signal
ŷ1(
n), and a second input port of the first adder circuit 402 receives the first error
signal e
2(
n). Thereby, the first decoupling signal
ŷ1(
n) deducts the
y1(
n) component from the first error signal
e2(
n), and outputs the deducted first error signal
e2(
n) (hereinafter, a signal
e2'(
n)) to the second ANC filtering unit 204. The signal
e2'(
n) received by the second ANC filtering unit 204 is substantially equal to
d2(
n)+
y2(
n)
. In other words, the second ANC filtering unit 204 is no longer interfered by the
first signal
y1(
n), and therefore can generate an effective anti-noise signal. In order to facilitate
the description of the embodiment in FIG. 7, the transfer function of the physical
channel 205 is represented as
S1(
z), and the transfer function of the first channel simulation filter 401 is represented
as
Ŝ1(
z).
[0068] On the other hand, since the mechanical appearance of the headphone is not an isolated
type in this embodiment, the external first microphone 201 will also be interfered
by the reverse of the echo noise inside the ear canal. Another physical channel 72
in this real environment is represented as
S2(
z) by the Z-domain transfer function. In other words, the transfer function
S2(
z) of the second physical channel 72 is used to represent the transmission between
the active noise cancellation integrated circuit 20 and the input of the first microphone
201. Similarly, after the anti-noise signals
y'
1(
n) and
y'
2(
n) output by the active noise cancellation integrated circuit 20 are transmitted through
the second physical channel 72,
x1(
n) represents an audio signal corresponding to the first anti-noise signal
y'
1(
n), and
x2(
n) represents an audio signal corresponding to the second anti-noise signal
y'2(
n). Regarding the actual audio signal transmission, the signals
x1(
n) and
x2(
n) are transmitted from the ear canal to the first microphone 201, thus the channel
response thereof is different from the channel response in the ear canal. Therefore,
the signals
x1(
n) and
x2(
n) are different from the audio signals
y1(
n) and
y2(
n).
[0069] In addition to receiving the signals
x1(
n) and
x2(
n), the first microphone 201 also receives an external noise signal
d1(
n). Accordingly, the external noise signal
d1(
n)
, the signals
x1(
n) and
x2(
n) are converted to a second error signal
e1(
n) by the first microphone 201. In addition, the external noise signal
d1(
n) is converted into a primary noise signal
d2(
n) after entering from the outside of the active noise cancellation headphone to the
inside of the active noise cancellation headphone. The primary noise signal
d2(
n) is substantially equal to the primary noise signal
d(
n) in FIG. 2.
[0070] If the second error signal e
1(n) is not appropriately processed, the second error signal
e1(n) received by the first ANC filtering unit 203 includes the signal
x2(
n). Due to the similar reasoning provided in the embodiment of FIG. 2, the first ANC
filtering unit 203 would be interfered by the signal
x2(
n) and the generated anti-noise signal thereof cannot effectively eliminate noise.
Thus, the signal
x2(
n) needs to be removed from the second error signal
e1(
n), such that the signal received by the first ANC filtering unit 203 does not contain
the signal
x2(
n).
[0071] Therefore, this embodiment provides a second decoupling unit 70 including a second
channel simulation filter 701 and a second adder circuit 702. Since the signal
x2(
n) is output by the physical channel 72, the second channel simulation filter 701 needs
to simulate the above physical channel 72 instead of simulating the physical channel
205 to effectively eliminate the signal
x2(
n) in the second error signal
e1(
n).
[0072] The second channel simulation filter 701 receives the second anti-noise signal
y'
2(
n) output by the second ANC filtering unit 204 to generate the second decoupling signal
x^
2(
n). The second decoupling signal
x^
2(
n) is substantially equal to the signal
x2(
n). Next, a first input port of the second adder circuit 702 receives the second decoupling
signal
x^
2(
n), and a second input port of the second adder circuit 702 receives the second error
signal
e1(
n). Thereby, the component of the signal
x2(
n) in the second error signal
e1(
n) is removed, and the removed second error signal
e1(
n) (hereinafter, a signal
e1' (
n)) is output to the first ANC filtering unit 203. The signal
e1' (
n) received by the first ANC filtering unit 203 is substantially equal to
d1(
n)+
x1(
n). The first ANC filtering unit 203 is not interfered by the signal
x2(
n), such that the generated first anti-noise signal
y'
1(
n) thereof is effective.
[0073] In this embodiment, a first path is from an output terminal of the first microphone
201, via the first ANC filtering unit 203, to an input terminal of each of the physical
channels 205 and 72. A second path is from an output terminal of the second microphone
202, via the second ANC filtering unit 204, to an input terminal of each of the physical
channels 205 and 72. The first path anti-noise signal is converted to the third signal
x1(
n) by the second physical channel 72. The second path anti-noise signal is converted
to the fourth signal x
2(n) by the second physical channel 72. In other words, the first path receives the
seco
nd error signal e1(n) with the component of the fourth signal x2(
n), so that the first ANC filtering unit 203 in the first path is interfered by the
fourth signal
x2(
n). The second decoupling unit 70 in this embodiment is used for removing the component
of the fourth signal x
2(n) from the first path based on the second anti-noise signal
y'
2(
n)
.
[0074] In another embodiment, only a single microphone is implemented, but there are two
active noise cancellation circuits in system. Referring to FIG. 8. FIG. 8 illustrates
a block diagram depicting an equivalent sampling time of an active noise cancellation
headphone according to a preferred embodiment of the present invention. In the embodiment
of FIG. 8, the active noise cancellation headphone adopts feedback noise cancellation
architecture. Referring to FIG. 8, in this embodiment, there is only the second microphone
202 (noise receiving microphone in an ear canal) in the active noise cancellation
headphone. However, in this embodiment, there are the first ANC filtering unit 203
and the second ANC filtering unit 204.
[0075] Different from the embodiment in FIG. 7, if the signal to be received by the first
ANC filtering unit 203 is not applied with a decoupling process, that is, the error
signal e(n) is without decoupling and is directly received by the first ANC filtering
unit 203, the first ANC filtering unit 203 will be affected by the interference of
the second signal y
2(n) instead of the signal x
2(n) of the embodiment of FIG. 7. Therefore, in order to effectively eliminate the
signal
y2(
n) in the error signal e(n), a channel simulation filter 801 in a second decoupling
unit 80 needs to simulate the above physical channel 205 instead of the physical channel
72 to generate the second decoupling signal
ŷ2(
n). Similarly, the second adder circuit 802 receives the second decoupling signal
ŷ2(
n) and the error signal
e(
n), subtracts the component of the signal
y2(
n) from the error signal
e(
n) by subtracting the second decoupling signal
ŷ2(
n) from the error signal e(n), and outputs the result to the first ANC filtering unit
203. The signal
e1'(
n) received by the first ANC filtering unit 203 is substantially equal to
d(
n)+
y1(
n), so that the first ANC filtering unit 203 would not be interfered by the signal
y2(
n), thus the first anti-noise signal
y'
1(
n) is generated to effectively cancel the noise.
[0076] That is to say, referring to FIG. 7 and FIG. 8. The embodiments of FIG. 7 and FIG.
8 adopt almost the same redundant elimination structure, and the only difference is
that the embodiment in FIG. 8 only has the second microphone 202. Since the methods
for eliminating redundant component(s) are similar, the detail description is omitted.
[0077] In this embodiment, a first path starts from an output terminal of the second microphone
202, and via the first ANC filtering unit 203, to an input terminal of the physical
channel 205. A second path starts from an output terminal of the second microphone
202, via the second ANC filtering unit 204, to an input terminal of the physical channel
205.
[0078] FIG. 9 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention. In FIG. 9, the active
noise cancellation headphone also adopts hybrid active noise cancellation architecture.
Referring to FIG. 9 and FIG. 8, the difference between FIG. 9 and FIG. 8 is that feedforward
noise cancellation is additionally added in FIG. 9, that is, the first microphone
201 and the third ANC filtering unit 91 are added.
[0079] For the first ANC filtering unit 203, if a signal to be received by the first ANC
filtering unit 203 is not applied with a decoupling process, the first ANC filtering
unit 203 would be interfered by the signals
y0(
n) and
y2(
n)
. Therefore, a channel simulation filter 901 and an adder circuit 902 in a third decoupling
unit 90 are used to eliminate the interference of the signal
y0(
n), and a second decoupling unit 80 is used to eliminate the interference of the signal
y2(
n)
. The principle of eliminating interference is the same as that of the previous embodiments.
Thus, the detail description is omitted.
[0080] For the second ANC filtering unit 204, if a signal to be received by the second ANC
filtering unit 204 is not applied with a decoupling process, the second ANC filtering
unit 204 would be interfered by the signals
y0(
n) and
y1(
n)
. Therefore, the channel simulation filter 901 and an adder circuit 903 in the third
decoupling unit 90 are used to eliminate the interference of the signal
y0(
n), and the first decoupling unit 40 is used to eliminate the interference of the signal
y1(
n). The principle of eliminating interference is the same as that of the previous embodiments.
Thus, the detail description is omitted. In addition, in this embodiment, in order
to simplify wiring complexity in component schematic diagram, relative positions between
the adding unit 206 and the second microphone 202 in FIG. 9 are reversed with that
between the adding unit 206 and the second microphone 202 in FIG. 8. People having
ordinary skill in the art should know that the relative position between the adding
unit 206 and the second microphone 202 in drawings cannot be used to limit the configuration
of the present invention.
[0081] According to the description above, this embodiment further includes a third path,
starting from an output terminal of the first microphone 201, via the third ANC filtering
unit 91, to an input terminal of the physical channel 205. A third anti-noise signal
y'
0(
n) output by the third ANC filtering unit 91 is, for example, the third path anti-noise
signal in this embodiment, and the third anti-noise signal
y'
0(
n) is converted to a third signal
y0(
n) by the physical channel 205. Since both the first path and the second path receive
the error signal e(n) containing the component of the third signal
y0(
n), the third decoupling unit 90 proposed in this embodiment removes the component
of the third signal
y0(
n) from the first path and the second path based on the third anti-noise signal
y'
0(
n).
[0082] In order to address the abovementioned issue, an embodiment of the present invention
provides an active noise cancellation method for stacking multiple anti-noise signals.
FIG. 10 illustrates a flowchart depicting an active noise cancellation method for
stacking multiple anti-noise signals according to a preferred embodiment of the present
invention. Referring to FIG. 10, the active noise cancellation method for stacking
multiple anti-noise signals includes the steps as follow.
[0083] In step S1001, a first path is provided, and a first path anti-noise signal is output,
wherein the first path anti-noise signal is converted to a first signal by a physical
channel, wherein the first path includes a first ANC filtering unit for generating
a first anti-noise signal. A second path is provided. The second path receives an
error signal including a component of the first signal, and outputs a second path
anti-noise signal to the physical channel, wherein the second path includes a second
ANC filtering unit for generating a second anti-noise signal, and wherein the second
path anti-noise signal is derived from the second anti-noise signal.
[0084] In step S1002, the component of the first signal is removed from the second path
based on the first anti-noise signal. As shown in FIG. 4, at an input of the second
ANC filtering unit 204, the first signal
y1(
n) is, based on the first anti-noise signal and by means of the first channel simulation
filter 401, removed from the error signal
e(
n) to be received by the second ANC filtering unit 204. Furthermore, as shown in FIG.
5, based on the first anti-noise signal and by means of the first channel simulation
filter 501 and the third ANC filtering unit 502, which has the same transfer function
as the second ANC filtering unit, a decoupling signal is generated, and the decoupling
process is applied at an output terminal of the second ANC filtering unit 204. Similarly,
as shown in FIG. 6, based on the first anti-noise signal and by means of the sound
channel analog filter 602 and the third ANC filtering unit 601, which has the same
transfer function as the second ANC filtering unit, a decoupling signal is generated,
and the decoupling process is applied at an output of the second ANC filtering unit
204. In other words, as long as there are at least two active noise cancellation filter
units and anti-noise signals generated by the active noise cancellation filter units
are coupled to each other, a decoupling signal can be generated by a specific one
of the anti-noise signals, to eliminate the specific anti-noise signal component in
a path of active noise cancellation filter units other than active noise cancellation
filter units generating the specific anti-noise signal. Thereby, the present invention
can eliminate the abovementioned mutual interference. The abovementioned embodiments
in FIG. 7, FIG. 8, and FIG. 9 are derived from the spirit or gist of the present invention.
Therefore, the present invention is not limited to FIG. 4, FIG. 5, and FIG. 6.
[0085] In step S1003, a playback is performed based on the first path anti-noise signal
and the second path anti-noise signal to cancel noise.
[0086] In summary, the spirit or gist of the present invention is to set multiple active
noise cancellation filtering unit in active noise cancellation apparatuses of active
noise cancellation headphones. Moreover, the redundant component(s) generated from
an output signal of active noise cancellation filtering units is/are canceled by a
decoupling process. Thus, an output noise cancellation signal from the active noise
cancellation apparatus would match the received noise relatively well such that the
received noise can be properly canceled.
[0087] In above embodiments, a filter circuit located at the first path included in the
active noise cancellation integrated circuit 20 is used for the ANC purpose. However,
this is for illustrative purposes only, and is not meant to be a limitation of the
present invention. In practice, any application using the proposed decoupling technique
falls with the scope of the present invention.
[0088] For example, an active noise cancellation integrated circuit using the proposed decoupling
technique may have an ANC function (e.g., a feedback ANC function) integrated with
a hearing aid (HA) function. The principle of HA is to amplify the sound picked up
by the reference microphone and then play back to a hearing-impaired user for hearing
loss compensation. The characteristics of the amplification are controlled by an HA
filter which is a non-ANC filter.
[0089] For another example, an active noise cancellation integrated circuit using the proposed
decoupling technique may have an ANC function (e.g., a feedback ANC function) integrated
with a pass-through (PT) function. PT is very similar to HA, and is to calibrate the
sound picked up by the reference microphone and then play back to the user to recover
the sound blocked or attenuated by the headphone/earphone shell. In some applications,
the PT function can be used to boost audio components in a high-frequency band that
is blocked or attenuated by the headphone/earphone shell. Hence, the user wearing
a headphone/earphone that operates in a PT mode may hear the ambient sound very similar
to that heard by the user without wearing the headphone/earphone. The compensation
is controlled by a PT filter which is a non-ANC filter.
[0090] For yet another example, an active noise cancellation integrated circuit using the
proposed decoupling technique may have an ANC function (e.g., a feedback ANC function)
integrated with a personal sound amplification (PSAP) function. As the name suggests,
PSAP is to amplify the sound but does not address other components of hearing loss.
Specifically, PSAP has not been approved as a medical device by the Food and Drug
Administration (FDA), and is classified as a wearable electronic product for occasional,
recreation use by a user who is not hearing impaired. The characteristics of the amplification
are controlled by a PSAP filter which is a non-ANC filter.
[0091] The ANC function (e.g., feedback ANC function) could cancel the low-frequency noise
picked up by an in-ear microphone acting as an error microphone, and is helpful to
reduce the occlusion effect caused by HA/PT/PSAP. However, the ANC function (e.g.,
feedback ANC function) will also cancel the sound played by the speaker of the headphone/earphone,
which reduces the performance of HA/PT/PSAP. The proposed decoupling technique mentioned
above can also be used to improve performance of HA/PT/PSAP provided by a non-ANC
filter through mitigating or cancelling the side effect caused by an ANC filter (e.g.,
a feedback ANC filter).
[0092] FIG. 11 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention. The active noise cancellation
headphone in FIG. 11 is similar to the active noise cancellation headphone in FIG.
4, and the difference is that the active noise cancellation integrated circuit 110
is used for stacking at least one anti-noise signal and at least one non-anti-noise
signal, and includes a non-ANC filtering unit (e.g., a digital filter) 1103 that takes
the place of the first ANC filtering unit 203 (e.g., a digital filter) shown in FIG.
4. Hence, the first decoupling unit 40 receives the non-anti-noise signal
y'
1(
n) output from the non-ANC filtering unit 1103 rather than the first anti-noise signal
y'
1(
n) output from the first ANC filtering unit 203, and removes the first signal
y1(
n) from the error signal e(n) captured by the second microphone 202 by electrical signal
processing. In this embodiment, the first path is from an output terminal of the first
microphone 201, via the non-ANC filtering unit 1103, to an input terminal of the physical
channel 205; and the second path is from an output terminal of the second microphone
202, via the second ANC filtering unit 204, to an input terminal of physical channel
205. Since the first signal
y1(
n) (which is derived from passing the non-anti-noise signal
y'
1(
n) through the physical channel 205) is removed from the second path through the first
decoupling unit 40, the intended purpose of the non-ANC filtering unit 1103 can be
achieved by mitigating or cancelling the side effect caused by the second ANC filtering
unit 204. That is, the feedback ANC does not cause loss of the first signal
y1(
n), and the intended purpose of the non-ANC filtering unit 1103 can be achieved without
performance degradation.
[0093] The present invention has no limitations on the non-ANC filtering unit 1103. The
non-ANC filtering unit 1103 may be set by any suitable non-ANC filter needed by an
application. For example, the non-ANC filtering unit 1103 may be an HA filter with
a weighting labeled as
WHA. For another example, the non-ANC filtering unit 1103 may be a PT filter with a weighting
labeled as
WPT. For yet another example, the non-ANC filtering unit 1103 may be a PSAP filter with
a weighting labeled as
WPSAP.
[0094] The active noise cancellation integrated circuit 110 shown in FIG. 11 and the active
noise cancellation integrated circuit 20 shown in FIG. 4 have the same circuit architecture
except generation of the filter output
y'
1(
n). As a person skilled in the art can readily understand the mathematical principle
of the active noise cancellation integrated circuit 110 shown in FIG. 11 after reading
above paragraphs directed to the active noise cancellation integrated circuit 20 shown
in FIG. 4, further description is omitted here for brevity.
[0095] FIG. 12 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention. The active noise cancellation
headphone in FIG. 12 is similar to the active noise cancellation headphone in FIG.
5, and the difference is that the active noise cancellation integrated circuit 110
is used for stacking at least one anti-noise signal and at least one non-anti-noise
signal, and includes the non-ANC filtering unit 1103 that takes the place of the first
ANC filtering unit 203 shown in FIG. 5. Hence, in this embodiment, the first decoupling
unit 50 receives the non-anti-noise signal
y'
1(
n) output from the non-ANC filtering unit 1103 rather than the first anti-noise signal
y'
1(
n) output from the first ANC filtering unit 203. Specifically, the first channel simulation
filter 501 is used to simulate the physical channel 205, and receive the non-anti-noise
signal
y'
1(
n) to generate the first decoupling signal
y1(
n), wherein the non-anti-noise signal y'
1(n) is obtained in a manner in which the external noise signal is received by the
first microphone 201, in turn applied with sampling and analog-to-digital conversion,
and further in turn processed by the non-ANC filtering unit 1103. Furthermore, the
second input port of the second adder circuit 504 receives the non-anti-noise signal
y'
1(n) output from the non-ANC filtering unit 1103 rather than the first anti-noise signal
y'
1(
n) output from the first ANC filtering unit 203.
[0096] It can be seen that although the second ANC filtering unit 204 is interfered by the
first signal
y1(
n), the interference is equivalently eliminated by the third ANC filtering unit 502
and the first adder circuit 503. Since the first signal
y1(
n) (which is derived from passing the non-anti-noise signal
y'
1(
n) through the physical channel 205) is removed from the second path through the first
decoupling unit 50, the intended purpose of the non-ANC filtering unit 1103 can be
achieved by mitigating or cancelling the side effect caused by the second ANC filtering
unit 204. That is, the feedback ANC does not cause loss of the first signal
y1(
n), and the intended purpose of the non-ANC filtering unit 1103 can be achieved without
performance degradation.
[0097] The present invention has no limitations on the non-ANC filtering unit 1103. The
non-ANC filtering unit 1103 may be set by any suitable non-ANC filter needed by an
application. For example, the non-ANC filtering unit 1103 may be an HA filter with
a weighting labeled as
WHA. For another example, the non-ANC filtering unit 1103 may be a PT filter with a weighting
labeled as
WPT. For yet another example, the non-ANC filtering unit 1103 may be a PSAP filter with
a weighting labeled as
WPSAP.
[0098] According to the mathematical principle of the linear system, the difference in the
configuration sequence does not substantially lead to the change of the result. For
example, in some embodiments, the non-anti-noise signal y'1(n) output from the non-ANC
filtering unit 1103 can be configured to be processed by the third ANC filtering unit
502 first, and then in turn processed by the first channel simulation filter 501.
[0099] The active noise cancellation integrated circuit 110 shown in FIG. 12 and the active
noise cancellation integrated circuit 20 shown in FIG. 5 have the same circuit architecture
except generation of the filter output
y'
1(
n). As a person skilled in the art can readily understand the mathematical principle
of the active noise cancellation integrated circuit 110 shown in FIG. 12 after reading
above paragraphs directed to the active noise cancellation integrated circuit 20 shown
in FIG. 5, further description is omitted here for brevity.
[0100] The abovementioned embodiment in FIG. 12 adopts a different decoupling method from
that in FIG. 11, but it can also eliminate the component of the redundant first signal
y1(
n). Another embodiment is proposed below, which can also eliminate the component of
the redundant first signal
y1(
n), such that people having ordinary skill in the art can implement the present invention
accordingly.
[0101] FIG. 13 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention. The active noise cancellation
headphone in FIG. 13 is similar to the active noise cancellation headphone in FIG.
6, and the difference is that the active noise cancellation integrated circuit 110
is used for stacking at least one anti-noise signal and at least one non-anti-noise
signal, and includes the non-ANC filtering unit 1103 that takes the place of the first
ANC filtering unit 203 shown in FIG. 6. In the embodiment in FIG. 13, a signal provided
by the first microphone 201 is processed to achieve the effect of decoupling. Hence,
the first decoupling unit 60 receives the non-anti-noise signal
y'
1(
n) output from the non-ANC filtering unit 1103 rather than the first anti-noise signal
y'
1(
n) output from the first ANC filtering unit 203. Specifically, the third ANC filtering
unit 601 receives the non-anti-noise signal
y'
1(
n) output by the non-ANC filtering unit 1103, and outputs the third anti-noise signal
y'
1(
n)
W2. Furthermore, the second input port of the first adder circuit 603 receives the non-anti-noise
signal
y'
1(
n) output from the non-ANC filtering unit 1103 rather than the first anti-noise signal
y'
1(
n) output from the first ANC filtering unit 203.
[0102] Furthermore, the operation of the third ANC filtering unit 601 is similar to that
of the third ANC filtering unit 502 in FIG. 12. The difference is that the non-anti-noise
signal
y'
1(
n) in the embodiment of FIG. 12 is first processed by the first channel simulation
filter 501, and then processed by the third ANC filtering unit 502. In this embodiment,
the non-anti-noise signal
y'
1(
n) is first processed by the third ANC filtering unit 601 and then processed by the
channel simulation filter 602. According to the mathematical principle of the linear
system, the abovementioned difference in the configuration sequence does not substantially
lead to the change of the result. The detail description is omitted. Accordingly,
in some embodiments, the non-anti-noise signal
y'
1(
n) can be configured to be processed by the channel simulation filter 602 first, and
then in turn processed by the third ANC filtering unit 601.
[0103] The first input port of the first adder circuit 603 receives the first decoupling
signal
ŷ1(
n)
W2, the second input port of the first adder circuit 603 receives the non-anti-noise
signal
y'
1(
n), and one of the two signals is subtracted from the other of the two signals. Then,
the subtracted signal and a signal on the path of the second ANC filtering unit 204
are interfered with each other through the second adder circuit 604 to eliminate the
component of the first signal
y1(
n) from the anti-noise signal [
d(
n)+
y1(
n)+
y2(
n)]
W2 output by the second ANC filtering unit 204. Specifically, the component
ŷ1(
n)
W2 in the signal [
y'1(
n)-
ŷ1(
n)
W2] output by the first adder circuit 603 is used to cancel the component [
y1(
n)
W2] in the anti-noise signal [
d(
n)+
y1(
n)+
y2(
n)]
W2 output by the second ANC filtering unit 204. Moreover, the primary noise signal
d(
n) in the anti-noise signal [
d(
n)+
y1(
n)+
y2(
n)]
W2 can be ignored. Accordingly, the signal output by the second adder circuit 604 is
[
y2(
n)
W2+
y'1(
n)]
, which can be further simplified as [
y'
2(
n)+
y'
1(
n)]. Since the first signal
y1(
n) (which is derived from passing the non-anti-noise signal
y'
1(
n) through the physical channel 205) is removed from the second path through the first
decoupling unit 60, the intended purpose of the non-ANC filtering unit 1103 can be
achieved by mitigating or cancelling the side effect caused by the second ANC filtering
unit 204. That is, the feedback ANC does not cause loss of the first signal
y1(
n), and the intended purpose of the non-ANC filtering unit 1103 can be achieved without
performance degradation.
[0104] The present invention has no limitations on the non-ANC filtering unit 1103. The
non-ANC filtering unit 1103 may be set by any suitable non-ANC filter needed by an
application. For example, the non-ANC filtering unit 1103 may be an HA filter with
a weighting labeled as
WHA. For another example, the non-ANC filtering unit 1103 may be a PT filter with a weighting
labeled as
WPT. For yet another example, the non-ANC filtering unit 1103 may be a PSAP filter with
a weighting labeled as
WPSAP.
[0105] The active noise cancellation integrated circuit 110 shown in FIG. 13 and the active
noise cancellation integrated circuit 20 shown in FIG. 6 have the same circuit architecture
except generation of the filter output
y'
1(
n). As a person skilled in the art can readily understand the mathematical principle
of the active noise cancellation integrated circuit 110 shown in FIG. 13 after reading
above paragraphs directed to the active noise cancellation integrated circuit 20 shown
in FIG. 6, further description is omitted here for brevity.
[0106] In the abovementioned embodiments, in-ear headphone is taken as an example. Since
the in-ear headphone has a good isolation effect between the internal microphone and
the external microphone, the noise received by the internal microphone cannot be received
by the external microphone. Therefore, in the abovementioned embodiments, echo noise
cannot affect the first microphone 201. The following embodiment is an example without
having good isolation.
[0107] FIG. 14 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone without good isolation between an ear canal and environment
according to a preferred embodiment of the present invention. The active noise cancellation
headphone in FIG. 14 is similar to the active noise cancellation headphone in FIG.
7, and the difference is that the active noise cancellation integrated circuit 110
is used for stacking at least one anti-noise signal and at least one non-anti-noise
signal, and includes the non-ANC filtering unit 1103 that takes the place of the first
ANC filtering unit 203 shown in FIG. 7.
[0108] Referring to FIG. 14, in this embodiment, the active noise cancellation headphone
is semi-in-ear headphone. Since a headphone shell 19 of this type of active noise
cancellation headphone cannot effectively block sound passing from the inside of the
active noise cancellation headphone to the outside of the active noise cancellation
headphone, the first microphone 201 disposed outside of the headphone would be interfered
by the echo noise inside the ear canal. Therefore, in addition to the first decoupling
unit 40, the active noise cancellation device of the above-mentioned active noise
cancellation headphone system further includes the second decoupling unit 70 whose
function is similar to that of the first decoupling unit 40.
[0109] This embodiment has the same concept as the aforementioned several embodiments. The
first decoupling unit 40 is used for generating a first decoupling signal according
to a non-anti-noise signal output by the non-ANC filtering unit 1103. Similarly, the
second decoupling unit 70 is used for generating a second decoupling signal according
to an anti-noise signal output by the second ANC filtering unit 204.
[0110] The first decoupling signal
y1(
n) is substantially equal to the first signal
y1(
n). The first error signal
e2(
n) received by the second microphone 202 is [
d2(
n)+
y1(
n)+
y2(
n)]. Next, the first decoupling signal
y1(n
) deducts the
y1(
n) component from the first error signal
e2(
n), and outputs the deducted first error signal
e2(
n) (hereinafter, a signal
e2'(
n)) to the second ANC filtering unit 204. The signal
e2'(
n) received by the second ANC filtering unit 204 is substantially equal to
d2(
n)+
y2(
n)
. In other words, the second ANC filtering unit 204 is no longer interfered by the
first signal
y1(
n)
.
[0111] The second decoupling unit 70 includes the second channel simulation filter 701 and
the second adder circuit 702. The second channel simulation filter 701 receives the
second anti-noise signal
y'
2(
n) output by the second ANC filtering unit 204 to generate the second decoupling signal
x^
2(
n). The second decoupling signal
x^
2(
n) is substantially equal to the signal
x2(
n). Next, the component of the signal
x2(
n) in the second error signal
e1(
n) is removed, and the removed second error signal
e1(
n) (hereinafter, a signal
e1' (
n)) is output to the non-ANC filtering unit 1103. The signal
e1' (
n) received by the non-ANC filtering unit 1103 is substantially equal to
d1(
n)+
x1(
n)
. The non-ANC filtering unit 1103 is not interfered by the signal
x2(
n).
[0112] The present invention has no limitations on the non-ANC filtering unit 1103. The
non-ANC filtering unit 1103 may be set by any suitable non-ANC filter needed by an
application. For example, the non-ANC filtering unit 1103 may be an HA filter with
a weighting labeled as
WHA. For another example, the non-ANC filtering unit 1103 may be a PT filter with a weighting
labeled as W
PT. For yet another example, the non-ANC filtering unit 1103 may be a PSAP filter with
a weighting labeled as
WPSAP.
[0113] The active noise cancellation integrated circuit 110 shown in FIG. 14 and the active
noise cancellation integrated circuit 20 shown in FIG. 7 have the same circuit architecture
except generation of the filter output
y'
1(
n). As a person skilled in the art can readily understand the mathematical principle
of the active noise cancellation integrated circuit 110 shown in FIG. 14 after reading
above paragraphs directed to the active noise cancellation integrated circuit 20 shown
in FIG. 7, further description is omitted here for brevity.
[0114] FIG. 15 illustrates a block diagram depicting an equivalent sampling time of an active
noise cancellation headphone with good isolation between an ear canal and environment
according to a preferred embodiment of the present invention. The active noise cancellation
headphone in FIG. 15 is similar to the active noise cancellation headphone in FIG.
9, and the difference is that the active noise cancellation integrated circuit 110
is used for stacking at least one anti-noise signal and at least one non-anti-noise
signal, and includes the non-ANC filtering unit 1103 that takes the place of the first
ANC filtering unit 203 shown in FIG. 9. Hence, in this embodiment, the first decoupling
unit 40 receives the non-anti-noise signal
y'
1(
n) output from the non-ANC filtering unit 1103 rather than the first anti-noise signal
y'
1(
n) output from the first ANC filtering unit 203, and the physical channel 205 transmits
the non-anti-noise signal
y'
1(
n) output from the non-ANC filtering unit 1103 rather than the first anti-noise signal
y'
1(
n) output from the first ANC filtering unit 203.
[0115] For the non-ANC filtering unit 1103, the channel simulation filter 901 and the adder
circuit 902 in the third decoupling unit 90 are used to eliminate the interference
of the signal
y0(
n) (which is derived from passing the third anti-noise signal
y'
0(
n) through the physical channel 205), and the second decoupling unit 80 is used to
eliminate the interference of the signal
y2(
n) (which is derived from passing the second anti-noise signal
y'
2(
n) through the physical channel 205). For the second ANC filtering unit 204, the channel
simulation filter 901 and the adder circuit 903 in the third decoupling unit 90 are
used to eliminate the interference of the signal
y0(
n) (which is derived from passing the third anti-noise signal
y'
0(
n) through the physical channel 205), and the first decoupling unit 40 is used to eliminate
the interference of the signal
y1(
n) (which is derived from passing the non-anti-noise signal
y'
1(
n) through the physical channel 205).
[0116] The present invention has no limitations on the non-ANC filtering unit 1103. The
non-ANC filtering unit 1103 may be set by any suitable non-ANC filter needed by an
application. For example, the non-ANC filtering unit 1103 may be an HA filter with
a weighting labeled as
WHA. For another example, the non-ANC filtering unit 1103 may be a PT filter with a weighting
labeled as
WPT. For yet another example, the non-ANC filtering unit 1103 may be a PSAP filter with
a weighting labeled as
WPSAP.
[0117] The active noise cancellation integrated circuit 110 shown in FIG. 15 and the active
noise cancellation integrated circuit 20 shown in FIG. 9 have the same circuit architecture
except generation of the filter output
y'
1(
n). As a person skilled in the art can readily understand the mathematical principle
of the active noise cancellation integrated circuit 110 shown in FIG. 15 after reading
above paragraphs directed to the active noise cancellation integrated circuit 20 shown
in FIG. 9, further description is omitted here for brevity.
[0118] FIG. 16 illustrates a flowchart depicting an active noise cancellation method for
stacking at least one anti-noise signal and at least one non-anti-noise signal according
to a preferred embodiment of the present invention. Referring to FIG. 16, the active
noise cancellation method for stacking at least one anti-noise signal and at least
one non-anti-noise signal includes the steps as follow.
[0119] In step S1601, a first path is provided, and a first path non-anti-noise signal is
output, wherein the first path non-anti-noise signal is converted to a first signal
by a physical channel, wherein the first path includes a non- ANC filtering unit for
generating a non-anti-noise signal. A second path is provided. The second path receives
an error signal including a component of the first signal, and outputs a second path
anti-noise signal to the physical channel, wherein the second path includes an ANC
filtering unit for generating an anti-noise signal, and wherein the second path anti-noise
signal is derived from the anti-noise signal.
[0120] In step S1602, the component of the first signal is removed from the second path
based on the non-anti-noise signal. As shown in FIG. 11, at an input of the second
ANC filtering unit 204, the first signal
y1(
n) is, based on the non-anti-noise signal and by means of the first channel simulation
filter 401, removed from the error signal e(n) to be received by the second ANC filtering
unit 204. As shown in FIG. 12, based on the non-anti-noise signal and by means of
the first channel simulation filter 501 and the third ANC filtering unit 502, which
has the same transfer function as the second ANC filtering unit, a decoupling signal
is generated, and the decoupling process is applied at an output terminal of the second
ANC filtering unit 204. As shown in FIG. 13, based on the non-anti-noise signal and
by means of the channel simulation filter 602 and the third ANC filtering unit 601,
which has the same transfer function as the second ANC filtering unit, a decoupling
signal is generated, and the decoupling process is applied at an output of the second
ANC filtering unit 204. As shown in FIG. 14, at an input of the second ANC filtering
unit 204, the first signal
y1(
n) is, based on the non-anti-noise signal and by means of the first channel simulation
filter 401, removed from the first error signal
e2(
n) to be received by the second ANC filtering unit 204; and at an input of the non-ANC
filtering unit 1103, the signal
x2(
n) is, based on the anti-noise signal and by means of the second channel simulation
filter 701, removed from the second error signal
e1(
n) to be received by the non-ANC filtering unit 1103.
[0121] In step S1603, a playback is performed based on the first path non-anti-noise signal
and the second path anti-noise signal to cancel noise.
[0122] Although the embodiment has been described as having specific components in FIGs.
1 to 9 and FIGs. 11-15, it should be noted that additional components may be included
to achieve better performance without departing from the spirit or gist of the invention.
Each steps of FIGs. 10 and 16 is arranged in a specific order to perform the aforementioned
operations. However, under the circumstance that does not violate the spirit or gist
of the invention, those skilled in the art can modify the sequence of these steps
on the premise of achieving the same effect. Thus, the present invention is not limited
thereto. Further, people having ordinary skill in the art should be apparent that
these processes can include more or fewer operations, which can be executed serially
or in parallel (e.g., using parallel processors or a multi-threading environment).
Therefore, the present invention is not limited thereto.
[0123] In above embodiments, an active noise cancellation integrated circuit may apply the
proposed decoupling technique to a combination of multiple ANC filters, or may apply
the proposed decoupling technique to a combination of non-ANC filter(s) and ANC filter(s).
In practice, the same decoupling concept for interference mitigation or performance
enhancement may be applied to any combination of filters employed by an active noise
cancellation integrated circuit. FIG. 17 illustrates a block diagram depicting an
equivalent sampling time of an active noise cancellation headphone between the ear
canal and environment according to a preferred embodiment of the present invention.
The active noise cancellation headphone in FIG. 17 is similar to the active noise
cancellation headphone in FIG. 4, and the difference is that the active noise cancellation
integrated circuit 170 includes a first filtering unit 1703 and a second filtering
unit 1704, where the first filtering unit 1703 takes the place of the first ANC filtering
unit 203 shown in FIG. 4, and the second filtering unit 1704 takes the place of the
second ANC filtering unit 204 shown in FIG. 4. Each of the first filtering unit 1703
and the second filtering unit 1704 may be set by any suitable digital filter, depending
upon actual design considerations. As a person skilled in the art can readily understand
the mathematical principle of the active noise cancellation integrated circuit 170
shown in FIG. 17 after reading above paragraphs directed to the active noise cancellation
integrated circuit 20 shown in FIG. 4 (or the active noise cancellation integrated
circuit 110 shown in FIG. 11), further description is omitted here for brevity.
[0124] While the invention has been described by way of example and in terms of the preferred
embodiments, it should be understood that the invention is not limited to the disclosed
embodiments. On the contrary, it is intended to cover various modifications and similar
arrangements (as would be apparent to those skilled in the art). Therefore, the scope
of the appended claims should be accorded the broadest interpretation so as to encompass
all such modifications and similar arrangements.
[0125] Those skilled in the art will readily observe that numerous modifications and alterations
of the device and method may be made while retaining the teachings of the invention.
Accordingly, the above disclosure should be construed as limited only by the metes
and bounds of the appended claims.