FIELD OF THE INVENTION
[0001] The invention relates to an electronic battery-powered hearing instrument, and to
a method for operating such a hearing instrument, as described in the preamble of
the corresponding independent claims.
BACKGROUND OF THE INVENTION
[0002] The term "hearing instrument" or "hearing device", as understood here, denotes on
the one hand hearing aid devices that are therapeutic devices improving the hearing
ability of individuals, primarily according to diagnostic results. Such hearing aid
devices may be Outside-The-Ear hearing aid devices or In-The-Ear hearing aid devices.
On the other hand, the term stands for devices which may improve the hearing of individuals
with normal hearing e.g. in specific acoustical situations such as in a very noisy
environment or in concert halls, or which may even be used in context with remote
communication or with audio listening for instance as provided by headphones.
[0003] The hearing devices as addressed by the present invention are so-called active hearing
devices which comprise at the input side at least one acoustical to electrical converter,
such as a microphone, at the output side at least one electrical to mechanical or
electroacoustic converter, such as a loudspeaker, and which further comprise a signal
processing unit for processing signals according to the output signals of the acoustical
to electrical converter and for generating output signals to the electrical input
of the electrical to mechanical output converter. In general, the signal processing
circuit may be an analog, digital or hybrid analog-digital circuit, and may be implemented
with discrete electronic components, integrated circuits, or a combination of both.
[0004] Many battery-powered hearing instruments or hearing devices provide access to the
battery in order to allow replacement by a user. It may then happen that small batteries,
especially disc-type batteries used in e.g. watches and in particular in hearing aids,
are inserted the wrong way around mechanically. As a result, their electrical polarity
with respect to the device's normal operating condition is inverted, that is, the
positive terminal of the battery is connected to the negative power terminal of the
device, and the negative terminal of the battery is connected to the positive power
terminal of the device. Consequently, the device will not operate and may even be
damaged.
[0005] In order to overcome this problem, US 5,661,420 proposes a rectifier circuit that
accepts, at a pair of input terminals, a power supply whose polarity may be oriented
either way, and provides, at a pair of output terminals, a voltage with a predefined
polarity. In order to reduce losses - as compared to a diode rectifier bridge - the
rectifier circuit comprises two transistor bridge circuits, with e.g. MOSFET transistors.
The transistor switches are opened or closed in order to connect the input and output
terminals according to the polarity at the input terminals.
Figure 1 shows this circuit as used in a hearing instrument according to this prior art. A
battery 3 powers the rectifier circuit 6 which in turn powers an amplifier 8 with
proper polarity, regardless of the orientation of the battery 3. The amplifier 8 accepts
input signals from a microphone 9 and drives a speaker 13.
[0006] When powering the hearing instrument by means of such a rectifier, all the electronic
circuits are powered by the rectifier. These circuits include primary function means
which implement the essential signal processing of the hearing instrument, and a loudspeaker
with an associated amplifier.
DESCRIPTION OF THE INVENTION
[0007] It is an object of the invention to create an electronic battery-powered hearing
instrument of the type mentioned initially, and a method for operating such a hearing
instrument that reduces circuit losses, noise and power consumption.
[0008] These objects are achieved by an electronic battery-powered hearing instrument, and
a method for operating such a hearing instrument according to the corresponding independent
claims.
[0009] The electronic battery-powered hearing instrument according to the invention comprises
- a first power supply terminal and a second power supply terminal arranged to contact
a battery,
- a rectifier circuit for providing a positive supply voltage and a negative supply
voltage regardless of a polarity of the battery relative to the first and second power
supply terminal,
- said primary function means arranged to provide at least one drive signal to a drive
circuit for driving electroacoustic conversion means by controlling electrical valve
means.
The drive circuit is electrically connected to the first power supply terminal and
to the second power supply terminal, and the electrical valve means or switching means
are polarity-independent, that is, they are able to operate regardless of the polarity
of the voltage applied to their terminals.
[0010] As a result, the current path from the battery to the electroacoustic conversion
means and back again preferably comprises at most two electrical valve means. This
in turn reduces a voltage drop over the valve means and corresponding power losses.
Furthermore, the low impedance of the connection from the supply to the power amplifier
output reduces the signal to noise ratio and distortion of the amplified signal.
[0011] The polarity independent valve means preferably comprise transistors, for example,
bipolar transistors or unipolar transistors such as field effect transistors, in particular
MOS transistors.
[0012] In a preferred embodiment of the invention, the valve means are configured and operated
as switches. That is, each valve is either in an "on" or conducting state, or in an
"off" or nonconducting state, and a transition time between these two states is negligible
with respect to the overall operation of the switch and the electroacoustic conversion
means. The drive circuit in this case preferably is a class D amplifier, that is,
an amplifier in which either a positive or a negative supply voltage or a zero voltage
is supplied to the terminals of the electroacoustic conversion means, and in which
an analog acoustical output signal is generated by pulse modulation of the voltage
at said terminals.
[0013] In a preferred embodiment of the invention, a polarity independent valve or switch
comprises two parallel transistors of complementary type. The two transistors are
controlled by drive signals that are inverted with respect to each other. In a preferred
embodiment of the invention, the two transistors are implemented as a complementary
MOS circuit.
[0014] Other complementary arrangements of transistors are possible, that is, arrangements
in which the characteristics of the two transistors complement one another. Control
signals for the individual transistors may be adapted by inverting one of them within
the valve or switch means itself. Alternatively, a drive circuit may provide inverted
and non-inverted drive signals and provide both to the valve or switch. In another
preferred embodiment of the invention, a "make before break" functionality is implemented
by the control of the different switches: That is, a switch is configured to break
(open) a first set of contacts before engaging (closing) some other new contacts.
This prevents the momentary connection of the old and new signal paths.
[0015] Depending on the polarity of the battery with respect to the power supply terminals,
one of the two transistors alternates between a partly conducting and a non-conducting
state, and the other one synchronously alternates between a conducting and a non-conducting
state, according to the drive signal.
[0016] In a further preferred embodiment of the invention, there is more than one rectifier
circuit arranged for powering the primary function means. For example, a first rectifier
circuit is configured to power an analog section of the primary function means, and
a second rectifier circuit is configured to power a digital section of the primary
function means. By having several rectifier circuits, interference between two or
more separately powered sections is reduced. Such an arrangement of multiple rectifiers
may be used together with the polarity-independent switching means as described above,
but also alone, i.e. without them.
[0017] The method for operating an electronic battery-powered hearing instrument, wherein
the drive circuit is electrically connected to the first power supply terminal and
to the second power supply terminal, and the electrical valve means are polarity-independent,
comprises the steps of
- providing primary function means with power from the battery via a first power supply
terminal and a second power supply terminal, and via a rectifier circuit for providing
a positive supply voltage and a negative supply voltage regardless of the polarity
of the battery relative to the first and second power supply terminal,
- providing, by means of the primary function means, at least one drive signal to a
drive circuit for driving an electroacoustic conversion means by controlling electrical
valve means,
- driving the electroacoustic conversion means regardless of the polarity of the battery
relative to the first and second power supply terminal.
[0018] This results in controlling, by means of the electrical valve means, a current through
the electroacoustic conversion means without incurring significant voltage drops and
power losses elsewhere than in the electrical valve means.
[0019] Further preferred embodiments are evident from the dependent patent claims. Features
of the method claims may be combined with features of the device claims and vice versa.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The subject matter of the invention will be explained in more detail in the following
text with reference to preferred exemplary embodiments which are illustrated in the
attached schematical drawings, in which:
- Figure 1
- shows a block diagram of a hearing instrument according to the state of the art;
- Figure 2
- shows a block diagram of the inventive hearing instrument; and
- Figure 3
- shows an internal structure of polarity-independent electric valve means.
[0021] The reference symbols used in the drawings, and their meanings, are listed in summary
form in the list of reference symbols. In principle, identical parts are provided
with the same reference symbols in the figures.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] Figure 2 schematically shows a block diagram of a hearing aid 10 according to the invention.
The hearing instrument 10 comprises a first power supply terminal 1 and a second power
supply terminal 2 arranged to contact a battery 3 which may be inserted either way
around. The first power supply terminal 1 and second power supply terminal 2 are electrically
connected to power a rectifier circuit 6 which, regardless of the polarity of the
battery 3, produces a negative supply voltage
Un at a negative supply line 11 and a positive supply voltage
Up at a positive supply line 12. The negative supply line 11 and positive supply line
12 power a primary function means 7 which comprises e.g. analog and/or digital signal
processing means according to the functions of the hearing instrument 10. The signal
processing means take as an input an audio signal from an input device - not shown
in the figures - such as a microphone, telephone coil, radio frequency (RF) receiver
etc. The signal processing means generate an output signal represented by one or more
drive voltages
Ud1,
Ud2,
Ud3,
Ud4 driving an output amplifier or drive circuit 20.
[0023] The drive circuit 20 is connected to an electroacoustic conversion means 13 such
as a loudspeaker. The circuit shown is also referred to as an H-bridge. The speaker
preferably is an electrodynamic speaker, but may also be based on other principles.
[0024] The drive circuit 20 is electrically connected to the first power supply terminal
1 and to the second power supply terminal 2, with minimal resistance and without any
further circuit elements of significant impedance, in particular without further electronic
switching means located in the connections between the drive circuit 20 and the first
power supply terminal 1 and the second power supply terminal 2, respectively.
[0025] The drive voltages
Ud1,
Ud2,
Ud3,
Ud4 are arranged to control polarity-independent electric valves 14, 15, 16, 17 of
the drive circuit 20. The electrical valve means 14, 15, 16, 17 are polarity-independent,
that is, they are able to operate regardless of the polarity of the voltage applied
to their power terminals, i.e. the terminals carrying the current that is controlled.
[0026] Depending on the internal nature of the valve means 14, 15, 16, 17, the drive voltages
Ud1,
Ud2,
Ud3,
Ud4 may be identical or may be inverted for some of the valve means 14, 15, 16, 17
by one or more corresponding inverters inside the primary function means 7. There
may be more than one drive signal per switch or valve. There may also be differences,
e.g. small shifts of edges, in the timing of the otherwise identical control signals,
in order to improve the signal quality of the output signals driving the speaker 13.
[0027] In a preferred embodiment of the invention, the electrical valve means 14, 15, 16,
17 are polarity-independent switches, in particular transmission gates, labelled TG-P
and TG-N. With the valves being switches, and in the configuration of
Figure 2, the drive circuit 20 forms a class D amplifier.
[0028] The transmission gates 14, 15, 16, 17 are arranged to be switched such that they
form a series configuration with the speaker 13. In particular, the drive circuit
20 is configured to establish, in accordance with the drive signal
Ud,
- either a current path connecting the first power supply terminal 1 via a first electrical
valve means 14, the speaker 13 and a second electrical valve means 15 to the second
power supply terminal 2,
- or a current path connecting the first power supply terminal 1 via a third electrical
valve means 16, the speaker 13 and a fourth electrical valve means 17 to the second
power supply terminal 2.
[0029] Furthermore, the drive circuit 20 may also be configured to establish a short circuit
current path for shorting the speaker 13 via the power supply terminals 1 or 2. This
can be done for instance by connecting the first power supply terminal 1 via the switch
14, the speaker 13 and the switch 16 back to the first power supply terminal 1, or
by connecting the second power supply terminal 2 via the switch 15, the speaker 13
and the switch 17 back to the second power supply terminal 2. In such a configuration,
energy stored in the coil of the speaker 13 is dissipated.
[0030] Thus,
- the first transmission gate 14 is electrically arranged between a first terminal of
the speaker 13 and the first power supply terminal 1,
- the second transmission gate 15 is electrically arranged between a second terminal
of the speaker 13 and the second power supply terminal 2,
- the third transmission gate 16 is electrically arranged between the second terminal
of the speaker 13 and the first power supply terminal 1, and
- the fourth transmission gate 17 is electrically arranged between the first terminal
of the speaker 13 and the second power supply terminal 2.
[0031] As a result, the drive circuit 20 is configured to establish, during operation, a
series circuit leading from the first power supply terminal 1 to the second power
supply terminal 2. Said series circuit comprises the speaker 13 and no more than two
electrical valve means 14, 15, 16, 17, that is, no further valve means or transistors
or switching elements. Thus, there occurs no corresponding voltage drop comparable
to the voltage drop in the electrical valve means 14, 15, 16, 17, and losses in the
switches or valves are reduced accordingly.
[0032] In a further preferred embodiment of the invention, the drive circuit 20 and the
primary function means 7 are arranged on an electronic circuit assembly 4 comprising
- a first set of connectors 21, 21' for powering the primary function means 7 from the
power supply terminals 1, 2 and
- a second set of connectors 22, 22' for powering the drive circuit 20 from the power
supply terminals 1, 2.
[0033] As a result, resistance of the amplifier circuits leading from the battery 3 to the
electroacoustic conversion means 13 is further reduced. Furthermore, the supply noise,
from a voltage drop caused by the current through the speaker and affecting the rectifier
circuit 6 and the primary function means 7 can be further reduced.
[0034] Figure 3 schematically shows an internal structure of the transmission gates. Each of the
transmission gates 14, 15, 16, 17 comprises a pair of complementary MOS transistors
31, 32. Depending on the polarity of the MOS transistors, the transmission gates are
labeled as TG-N or TG-P, respectively. The transistors forming a pair are driven by
gate signals inverted with respect to each other by means of an inverter 18. The well
or substrate connections of the transistors are made to the rectified supply voltages,
i.e. to the positive supply voltage Up (for PMOS transistors) and the negative supply
voltage
Un (for NMOS transistors).
[0035] With such transmission gates, the first and fourth transmission gate 14, 17 are preferably
controlled by the same drive voltage
Ud1 =
Ud4, and the second and third transmission gate 15, 16 are preferably controlled by
the same drive voltage Ud2 =
Ud3, which is inverted with respect to
Ud1 =
Ud4 during operation of the speaker 13. For turning off a current flow through the
speaker 13 and the battery, for example all drive voltages are set to the same value,
i.e.
Ud1 =
Ud2 =
Ud3 =
Ud4.
[0036] When the polarity of the battery 3 is inverted, the signal processing in the primary
function means 7 can work as before, without having to be aware of the polarity of
the inserted battery, and the polarity of the speaker signal is inverted. This corresponds
to a 180° phase shift and is not perceptible to the user. However, in another embodiment,
this is compensated by detecting the polarity and adapting the drive signals accordingly.
[0037] While the invention has been described in present preferred embodiments of the invention,
it is distinctly understood that the invention is not limited thereto, but may be
otherwise variously embodied and practised within the scope of the claims.
[0038] Although the features and advantages of the invention are explained in terms of hearing
instruments, they may be applied in an analogous fashion to arbitrary other devices
in which the objects according to the invention arise.
List of designations
[0039]
- 1
- first power supply terminal
- 2
- second power supply terminal
- 3
- battery
- 4
- electronic circuit assembly (hybrid)
- 6
- rectifier circuit
- 7
- primary function means
- 8
- amplifier
- 9
- microphone
- 10
- hearing instrument
- 11
- negative supply line
- 12
- positive supply line
- 13
- electroacoustic conversion means, speaker
- 14
- first transmission gate
- 15
- second transmission gate
- 16
- third transmission gate
- 17
- fourth transmission gate
- 18
- inverter
- 20
- drive circuit
- 21, 21'
- first set of connectors
- 22, 22'
- second set of connectors
- 31
- first transistor
- 32
- second transistor
- Un
- negative supply voltage
- Up
- positive supply voltage
- Ud
- drive voltage
1. An electronic battery-powered hearing instrument (10) comprising
- a first power supply terminal (1) and a second power supply terminal (2) arranged
to contact a battery (3),
- at least one rectifier circuit (6) for providing a positive supply voltage (Up) and a negative supply voltage (Un) regardless of a polarity of the battery (3) relative to the first and second power
supply terminal (2),
- primary function means (7) arranged to provide at least one drive signal (Ud) to a drive circuit (20) for driving an electroacoustic conversion means (13), by
controlling electrical valve means (14, 15, 16, 17),
characterised in that the drive circuit (20) is electrically connected to the first power supply terminal
(1) and to the second power supply terminal (2) and
in that the electrical valve means (14, 15, 16, 17) are polarity-independent.
2. The hearing instrument (10) according to claim 1, wherein the drive circuit (20) is
configured to establish, during operation, a series circuit leading from the first
power supply terminal (1) to the second power supply terminal (2), said series circuit
comprising the electroacoustic conversion means (13) and no more than two electrical
valve means (14, 15; 16,17).
3. The hearing instrument (10) according to claim 2, wherein the drive circuit (20) is
configured to establish, in accordance with the drive signal (
Ud),
- a current path connecting the first power supply terminal (1) via a first electrical
valve means (14), the electroacoustic conversion means (13) and a second electrical
valve means (15) to the second power supply terminal (2),
- or a current path connecting the first power supply terminal (1) via a third electrical
valve means (16), the electroacoustic conversion means (13) and a fourth electrical
valve means (17) to the second power supply terminal (2).
4. The hearing instrument (10) according to claim 3, wherein the drive circuit (20) is
a class D amplifier and the electrical valve means (14, 15, 16, 17) are CMOS transmission
gates.
5. The hearing instrument (10) according to claim 4, wherein the CMOS transmission gates
comprise individual PMOS and NMOS transistors, and the substrate connections of said
transistors are connected to the positive supply voltage (Up) and the negative supply voltage (Un), respectively.
6. The hearing instrument (10) according to one of the preceding claims, wherein each
of the polarity-independent electrical valve means (14, 15, 16, 17) comprises a pair
of complementary transistors (31, 32).
7. The hearing instrument (10) according to one of the preceding claims, wherein the
drive circuit (20) and the primary function means (7) are arranged on an electronic
circuit assembly (4) comprising a first set of connectors (21, 21') for powering the
primary function means (7) from the power supply terminals (1, 2) and a second set
of connectors (22, 22') for powering the drive circuit (20) from the power supply
terminals (1, 2).
8. The hearing instrument (10) according to one of the preceding claims, comprising a
first rectifier circuit configured to power a first section of the primary function
means, and a second rectifier circuit configured to power a second section of the
primary function means.
9. A method for operating an electronic battery-powered hearing instrument (10), comprising
the steps of
- providing primary function means (7) with power from the battery (3) via a first
power supply terminal (1) and a second power supply terminal (2), and via at least
one rectifier circuit (6) for providing a positive supply voltage (Up) and a negative supply voltage (Un) regardless of the polarity of the battery (3) relative to the first and second
power supply terminal (2),
- providing, by means of the primary function means (7), at least one drive signal
(Ud) to a drive circuit (20) for driving an electroacoustic conversion means (13) by
controlling electrical valve means (14, 15, 16, 17),
characterised in that the drive circuit (20) is electrically connected to the first power supply terminal
(1) and to the second power supply terminal (2),
in that the electrical valve means (14, 15, 16, 17) are polarity-independent, and
in that the method comprises the step of
- driving the electroacoustic conversion means (13) regardless of the polarity of
the battery (3) relative to the first and second power supply terminal (2).
10. The method according to claim 9, comprising the step of the drive circuit (20) establishing
a series circuit leading from the first power supply terminal (1) to the second power
supply terminal (2), said series circuit comprising the electroacoustic conversion
means (13) and no more than two electrical valve means (14, 15; 16,17).
11. The method according to claim 10, comprising the step of the drive circuit (20) establishing,
in accordance with the drive signal (
Ud),
- a current path connecting the first power supply terminal (1) via a first electrical
valve means (14), the electroacoustic conversion means (13) and a second electrical
valve means (15) to the second power supply terminal (2),
- or a current path connecting the first power supply terminal (1) via a third electrical
valve means (16), the electroacoustic conversion means (13) and a fourth electrical
valve means (17) to the second power supply terminal (2).