BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to radio pagers, and more specifically to
a sound alarm circuit for such radio pagers which generates an alert tone of escalating
sound levels.
[0002] A radio pager having the capability of successively escalating the sound level of
an alert tone is described in japanese Patent Publication 63-252030 (Tokkaisho). According
to the prior art technique, constant audio frequency pulses are modulated with a variable
duty tone pattern that identifies particular incoming pages. The duty ratio of the
tone pattern is successively increased to increase the sound level of the tone.
[0003] One serious disadvantage of the prior art technique is that since the sound level
is controlled by the duty ratio of a tone pattern, the alert tone patterns as standardized
by the Post Office Code Standardization Advisory Group (POCSAG) cannot be employed
for escalating alert tones.
SUMMARY OF THE INVENTION
[0004] It is therefore an object of the present invention to provide a radio pager that
enables internationally standardized alert tone patterns to be employed for alerting
users with an escalating sound level.
[0005] According to the present invention, the radio pager comprises a receiver for receiving
a paging signal containing a unique identifier identifying the own radio pager and
an alert tone pattern. A pulse generating circuit generates audio-frequency pulses
having a duty ratio increasing as a function of time in response to receipt of the
paging signal. A modulating means is provided for modulating the variable duty pulses
with the alert tone pattern for applying the modulated pulses to a loudspeaker.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The present invention will be described in further detail with reference to the accompanying
drawings, in which:
Fig. 1 is a block diagram of a radio pager of the present invention;
Fig. 2 is a block diagram of a sound alarm circuit of this invention;
Fig. 3 is a waveform diagram associated with the sound alarm circuit of Fig. 2;
Fig. 4 is a waveform diagram of the tone pulses modulated with a POCSAG A-code tone
pattern;
Fig. 5 is a block diagram of a modified form of the sound alarm circuit;
Fig. 6 is a waveform diagram associated with the sound alarm circuit of Fig. 5;
Fig. 7 is a block diagram of an alternative form of the sound alarm circuit; and
Fig. 8 is a waveform diagram associated with the sound alarm circuit of Fig. 7.
DETAILED DESCRIPTION
[0007] A radio pager of the present invention as represented in Fig. 1 comprises a front
end 2 for converting paging signals received by antenna 1 to baseband signals for
coupling to a waveshaper 3. The output of waveshaper 3 is applied to a decoder 4 in
which the received signal is checked for a coincidence between a pager identifier
contained in it and the one stored in a PROM (programmable read only memory) 5. On
detecting a coincidence, decoder 4 alerts a sound alarm circuit 6 with a POCSAG (Post
Office Code Standardization Advisory Group) alert tone signal having one of predetermined
tone patterns or cadences. For example, one such cadence is a cyclic sequence of 7/8-second
ON and 1/8-second OFF. Sound alarm circuit 6 modulates the tone signal with a variable
duty pulse sequence and activates a loudspeaker 7. A reset switch 8 is connected to
the decoder 4 to be operated when the user answers an incoming page.
[0008] As shown in Fig. 2, sound alarm circuit 6 comprises an AND gate 10 that is responsive
to an enable signal from decoder 4 to pass high-frequency clock pulses from a clock
source 9 to frequency dividers 11 and 12, and further to an up-counter 13 during the
time the pager is being alerted. As shown in Fig. 3, frequency divider 11 divides
the frequency of the clock to produce an output whose frequency determines the pitch
of the alert tone, typically at 2.6 kHz, and frequency divider 12 divides that clock
frequency so that its output determines the rate at which the duty ratio of the 2.6-kHz
pulse sequence is varied. Typically, the duty ratio is stepwisely varied at 6-second
intervals. The output of frequency divider 11 is applied to the up-counter 13 as a
reset pulse so that its output represents a digital count value which continuously
increments in response to the clock pulse until it rapidly drops to zero in response
to the reset pulse. On the other hand, the output of frequency divider 12 is applied
to a down-counter 15 to produce a decremental binary count value which represents
the varying rate of the duty ratio. A monostable multivibrator 14 is provided for
producing a pulse for clearing the contents of down-counter 15 as soon as the pager
is alerted.
[0009] The digital output of down-counter 15 is applied to a binary-to-duty converter 16
which converts it to a digital value representing the duty ratio of the 2.6-kHz pulse
sequence for each 6-second interval. In a typical example, binary-to-duty converter
16 successively generates outputs representing duty ratios of 12.5 %, 25 %, 33 % and
50 %. The outputs of binary-to-duty converter 16 and up-counter 13 are applied to
a digital comparator 17 in which they are compared with each other to produce a high-level
output when the digital value of counter 13 is greater than the output of binary-to-duty
converter 16. It is seen therefore that the output of comparator 17 is a sequence
of constant-frequency pulses of a variable duty ratio which increases stepwisely at
6-second intervals as shown in Fig. 3. From the tone quality standpoint, the maximum
duty ratio is set 50 % as described above.
[0010] The output of comparator 17 is applied to an AND gate 18 to which a POCSAG tone pattern,
say A-code pattern, is also applied. In this way, the variable duty 2.6 kHz pulse
sequence is modulated by the POCSAG A-code pattern as shown in Fig. 4 and applied
through an amplifier 19 to the speaker 7. Loudspeaker 7 has a narrow band of frequency
response characteristic. This characteristic is sufficient to suppress the harmonic
components of the modulated alert tone pulse which may otherwise cause changes in
tone quality with variations of the duty ratio.
[0011] Therefore, the POCSAG tone pattern can be used for generating an alert tone with
successively escalating sound levels.
[0012] A modified form of the sound alarm circuit 6 is shown in Fig. 5. In this modification,
a programmable counter 2b is used instead of the up-counter 13 and comparator 17.
Programmable counter 20 is clocked by the output of AND gate 10 and reset by the output
of frequency divider 11. The output of binary-to-duty converter 16 it applied to programmable
counter 20 as a preset count value which decrement at 6-second intervals in response
to the output of frequency divider 12 (Fig. 6), and hence the duty ratio of the tone
pulses generated by programmable counter 20 increases with the decrease in the preset
count value.
[0013] Alternatively, the present invention can be further modified as shown in Fig. 7 in
which the down-counter is replaced with an up-counter 31 and binary-to-duty converter
32 transforms the stepwisely incremental value of the output of counter 31 to a stepwisely
incremental duty ratio. A flip-flop 30 is provided having a set input terminal connected
to the output of frequency divider 11 and a reset input terminal connected to the
output of programmable counter 34 whose program input is connected to the output of
binary-to-duty converter 32. An AND gate 33 is responsive to the output of flip-flop
30 to pass the output of AND gate 10 to the clock input of programmable counter 34.
The output of flip-flop 30 is further applied to the reset input of programmabie counter
34 and one input of AND gate 18.
[0014] As shown in Fig. 8, flip-flop 30 is triggered into a high-level, set condition in
response to each output pulse from frequency divider 11 to allow clock pulses from
AND gate 10 to pass through AND gate 33 to the programmable counter 34. The latter
produces a high-level output when the duty representing count value is reached and
resets the flip-flop 30 to a low-level condition, producing a tone pulse having a
stepwisely incremental duty ratio.
[0015] The foregoing description shows only one preferred embodiment of the present invention.
Various modifications are apparent to those skilled in the art without departing from
the scope of the present invention which is only limited by the appended claims. Therefore,
the embodiment shown and described is only illustrative, not restrictive.
1. A radio pager comprising:
receive means for receiving a paging signal containing a unique identifier identifying
said radio pager and an alert tone pattern;
pulse generating means for generating constant audio frequency pulses having a
duty ratio increasing as a function of time in response to receipt of said paging
signal;
modulating means for modulating said pulses with said alert tone pattern; and
sound generating means activated by said modulated pulses.
2. A radio pager as claimed in claim 1, wherein said alert tone pattern is a POCSAG (Post
Office Code Standardization Advisory Group) tone pattern.
3. A radio pager as claimed in claim 1, wherein said pulse generating means comprises:
a clock source for generating pulses at a clock frequency;
a first frequency divider for dividing the clock frequency of said pulses to produce
pulses at an audio frequency;
a second frequency divider for dividing the clock frequency of said pulses to produce
pulses at a frequency much lower than said audio-frequency;
means responsive to each of the audio frequency pulses for generating a series
of first digital values which increase synchronously with said clock frequency pulses;
means for generating second digital values which successively decrease in response
to said lower frequency pulses;
means for comparing said first and second digital values to produce an output signal
when said first digital values are greater than said second digital values, said modulating
means being coupled to said comparing means.
4. A radio pager as claimed in claim 1, wherein said pulse generating means comprises:
a clock source for generating pulses at a clock frequency;
a first frequency divider for dividing the clock frequency of said pulses to produce
pulses at an audio frequency;
a second frequency divider for dividing the clock frequency of said pulses to produce
pulses at a frequency much lower than said audio-frequency;
means for generating digital values which successively decrease in response to
said lower frequency pulses; and
presettable counter means having a count value successively preset to said digital
values, said presettable counter means being responsive to each of the audio frequency
pulses for counting said clock frequency pulses to produce an output pulse having
a leading edge coinciding with time at which the count of the clock frequency pulses
reaches the preset value and a trailing edge coinciding with each of said audio frequency
pulses, said modulating means being coupled to said presettable counter means.
5. A radio pager as claimed in claim 1, wherein said pulse generating means comprises:
a clock source for generating pulses at a clock frequency;
a first frequency divider for dividing the clock frequency of said pulses to produce
pulses at an audio frequency;
a second frequency divider for dividing the clock frequency of said pulses to produce
pulses at a frequency much lower than said audio-frequency;
means for generating digital values which successively increase in response to
said lower frequency pulses; and
bistable means arranged to be triggered into a first output state in response to
each of the audio frequency pulses and triggered into a second output state in response
to a reset signal applied thereto, said modulating means being coupled to said bistable
means; and
presettable counter means having a count value successively preset to said digital
values, said presettable counter means being responsive to the first output state
of said bistable means for counting said clock frequency pulses to produce an output
pulse to said bistable means as said reset signal the count of the clock frequency
pulses reaches the preset value.