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DESCRIPTION JP2005045546

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DESCRIPTION JP2005045546
PROBLEM TO BE SOLVED: In a digital amplifier circuit, if a beep is emitted immediately after the
power is turned on, a popping noise is generated because the signal level largely changes.
SOLUTION: A confirmation sound generation circuit 10 for generating a beep sound, a reference
signal generation circuit 20 for generating a reference level signal for determining a reference
level of the beep sound, and an adder 22 for adding and outputting these outputs The reference
level signal is configured to gradually change from the power off level to the reference level of
the audio signal. Since the reference level (DC level) changes gradually and continuously between
power on and voice output, no pop noise occurs even if a beep is output immediately after power
on. [Selected figure] Figure 1
Digital amplifier circuit
[0001]
The present invention relates to a digital amplifier circuit, and more particularly to a digital
amplifier circuit that drives a speaker with a binary signal.
[0002]
In electronic devices, such as car stereos and portable compact disc players, where the user may
operate without looking directly at the device body, an operation confirmation sound, so-called
beep sound, informs the user that the operation button has been pressed. It is an important
feature.
[0003]
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1
As a conventional operation confirmation sound output circuit, there is one disclosed in Patent
Document 1, for example.
FIG. 9 shows a block diagram of a conventional operation confirmation sound output circuit.
In this conventional operation confirmation sound output circuit, the binary signal output from
the microcomputer chip 3 is added using the amplifier 2, the capacitor 5 and the resistor 6 to the
output of the amplifier 1 for amplifying the analog audio signal. In this case, the amplitude
adjustment is performed by the resistor 4 and the volume adjustment circuit 7.
[0004]
On the other hand, with the progress of digitization of devices, digital amplifier circuits that drive
speakers with digital signals instead of analog audio signals are being put to practical use. An
example of the digital amplifier circuit is disclosed in Patent Document 2. In such a digital
amplifier circuit, the operation confirmation sound is added to the analog voice signal by the
configuration of FIG. 9 in order to drive the speaker directly with a binary signal output by a
PWM (Pulse Width Modulation) waveform generation circuit or the like. I can not do it.
[0005]
FIG. 10 shows a block diagram of a conventional digital amplifier circuit having an operation
confirmation sound output function, and FIG. 11 shows an audio signal outputted by the
conventional digital amplifier circuit. Although the output of the digital amplifier circuit is a
binary signal, it is difficult to understand intuitively, so in FIG. 11, it is shown as a smoothed
analog waveform.
[0006]
In FIG. 10, 9 is an audio processing circuit that inputs a digital audio signal, performs
oversampling processing, noise shaping processing, etc., and outputs it, 10 is a confirmation
sound generation circuit that generates an operation confirmation sound signal (digital data), Is a
switch for selecting and outputting either the output of the audio processing circuit 9 or the
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operation confirmation sound signal according to the instruction of the system control circuit 23,
and 13 is a PWM modulation for converting the signal output from the switch 11 into a PWM
signal A circuit 14 is an inverter for driving the speaker 15.
[0007]
The operation of the conventional digital amplifier circuit configured as described above will be
described.
When outputting music or the like, the system control circuit 12 connects the switch 11 to the
audio processing circuit 9 and supplies the output of the audio processing circuit 9 to the PWM
modulation circuit 13. The PWM modulation circuit 13 PWM-modulates the input signal and
outputs it to the inverter 14. The inverter 14 inverts the input binary signal and outputs it to the
speaker 15. The speaker 15 operates as a low pass filter, and a binary signal is output as analog
voice.
[0008]
When an instruction is given from the outside, the system control means 23 connects the switch
11 to the confirmation sound generation circuit 10 side, and supplies an operation confirmation
sound signal to the PWM modulation circuit 13. The PWM modulation circuit 13 PWM
modulates the operation confirmation sound signal, and supplies it to the speaker 15 via the
inverter 14. As a result, an operation confirmation sound is output from the speaker 15 (t1 in
FIG. 11). After a predetermined time has elapsed, the system control circuit 12 returns the switch
11 to the audio processing circuit 9 side to stop the output of the operation confirmation sound
(t2 in FIG. 11). JP-A-10-289504 (page 2-5, FIG. 1) JP-A-9-46787 (page 2-4, FIG. 1)
[0009]
Application of the digital amplifier circuit to portable electronic devices is in progress because of
high power supply efficiency. In portable electronic devices, in order to reduce power
consumption, it is effective to turn off the power of the digital amplifier circuit when not
outputting audio and turn on the power of the digital amplifier circuit when instructed from the
outside. . However, the output of the digital amplifier circuit is "L" level when the power is not
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supplied, and when the switch 11 is connected to the confirmation sound generation circuit 10
according to the external instruction, the level of the signal supplied to the speaker 15 is Because
it changes rapidly, noise called "pop noise" or "click sound" is generated.
[0010]
The present invention has been made in view of the above problems, and it is an object of the
present invention to realize a digital amplifier circuit capable of producing an operation
confirmation sound without producing a pop noise immediately after the power is turned on.
[0011]
The digital amplifier circuit according to claim 1 of the present invention is an audio processing
circuit which receives a digital audio signal, performs predetermined processing and outputs the
signal, and an operation confirmation sound signal which generates a sound for confirming the
operation by the user. A confirmation sound generation circuit to generate, a reference signal
generation circuit generating a reference level signal which is a reference level of the operation
confirmation sound, an addition circuit adding the operation confirmation sound signal and the
reference level signal, and A selection circuit which selects and outputs one of an output of an
audio processing circuit and an output of the addition circuit, and an output of the selection
circuit is converted into a binary signal, and the binary signal directly or low pass And a drive
circuit for driving an external speaker via a filter, wherein the reference signal generation circuit
is configured to set the reference level signal from a level at power-off to a reference level of the
digital audio signal. Rui up to the level of power off from the reference level of the digital audio
signal, in which gradually changing, it is characterized in.
[0012]
With this configuration, when outputting the operation confirmation sound immediately after the
power is turned on, the operation confirmation sound can be output without generating a
popping noise.
[0013]
A digital amplifier circuit according to claim 2 of the present invention is the digital amplifier
circuit according to claim 1, wherein the adding circuit is configured to generate the operation
confirmation sound when the reference level signal is larger than the amplitude of the operation
confirmation sound signal. And adding the signal and the reference level signal.
[0014]
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With this configuration, the operation confirmation sound can be output without distortion of the
waveform of the operation confirmation sound.
[0015]
A digital amplifier circuit according to a third aspect of the present invention is the digital
amplifier circuit according to the first aspect, wherein the confirmation sound generation circuit
changes the amplitude of the operation confirmation sound signal in accordance with the
reference level signal. , Is characterized.
[0016]
With this configuration, it is possible to output the operation confirmation sound without
distorting the waveform of the operation confirmation sound while making the time delay from
the power-on almost zero.
[0017]
A digital amplifier circuit according to a fourth aspect of the present invention is the digital
amplifier circuit according to any one of the first to third aspects, wherein the addition circuit is
configured to confirm the operation while the reference level signal is changing. The sound
signal and the reference level signal are added, and the addition result is continuously output to
the drive circuit.
[0018]
With this configuration, it is possible to mask noise generated by the change of the reference
level signal with the operation confirmation sound, and to reduce the discomfort given to the
user.
[0019]
The digital amplifier circuit according to the present invention has a reference signal generating
circuit that generates a reference level signal that determines the DC level of the operation
confirmation sound, and is configured to gradually change the reference level signal so that no
pop noise occurs. Since it is a thing, it is possible to output an operation confirmation sound
without generating a pop noise even immediately after the power is turned on.
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As a result, when a digital amplifier circuit is applied to a portable electronic device, the power
supply of the digital amplifier circuit is stopped, and power saving is achieved, and a userfriendly electronic device that responds quickly to user operations is realized. It is possible to
[0020]
Further, according to the digital amplifier circuit of the present invention, by operating the
output timing of the operation confirmation sound and the amplitude of the operation
confirmation sound according to the amplitude of the reference level signal, the operation
confirmation sound is not distorted. The time from power-on to the output of the operation
confirmation sound can be shortened as much as possible, and the practical effect is extremely
high.
[0021]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
1 to 8 are diagrams for explaining digital amplifier circuits according to the second and third
embodiments of the present invention.
In the drawings, the same or corresponding portions are denoted by the same reference
characters, and description thereof will not be repeated.
[0022]
First Embodiment FIG. 1 is a block diagram of a digital amplifier circuit according to a first
embodiment of the present invention, and FIG. 2 is a diagram showing an audio signal output
from the digital amplifier circuit according to the first embodiment.
[0023]
Although the output of the digital amplifier circuit is a binary signal, it is shown as a smoothed
analog waveform as in FIG.
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FIG. 3 is a flowchart of processing performed by the system control circuit 23.
[0024]
In FIG. 1, 9 is an audio processing circuit that performs oversampling processing and noise
shaping processing on the input digital audio signal, 10 is a confirmation sound generation
circuit that generates an operation confirmation sound, 11 is a PWM modulation circuit 13
Switch for selecting a signal to be supplied, 13 is a PWM modulation circuit for PWM modulating
and outputting the input signal, 14 is an inverter for inverting and outputting an output of the
PWM modulation circuit 13, 15 is an output of the inverter 14; A speaker for converting into an
analog voice, 20 a reference signal generating circuit for generating a reference level signal for
determining a DC level of the operation confirmation sound, 21 a switch for stopping the output
of the confirmation sound generating circuit 10, 22 an output of the switch 21; An adder for
adding the reference level signal, 23 is a switch 11, a switch 21, and a reference signal
generation circuit 2 A system control circuit for controlling.
[0025]
The operation of the digital amplifier circuit of Embodiment 1 configured as described above will
be described.
In general, when audio is output, the system control circuit 23 connects the switch 11 to the
audio processing circuit 9 side, and supplies the digital audio signal processed by the audio
processing circuit 9 to the PWM modulation circuit 13.
The PWM modulation circuit 13 PWM-modulates the input signal and supplies it to the speaker
15 via the inverter 14.
The speaker 15 converts the input signal into analog voice and outputs it.
[0026]
When the power of the digital amplifier circuit is turned on, the output of the inverter 14 before
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turning on is at the "L" level.
When the power is turned on, the reference signal generation circuit 20 outputs a reference level
signal 20a corresponding to the "L" level.
Further, the system control circuit 23 opens the switch 21 and connects the switch 15 to the side
of the adder 22 so that the reference level signal is PWM-modulated to enter the speaker 15
(S31 in FIG. 3).
[0027]
Thereby, the digital amplifier circuit drives the speaker 15 at the “L” level immediately after
the power is turned on (t3 in FIG. 2).
Driving at "L" level means driving at the same level as when the power is off.
[0028]
Next, system control circuit 23 instructs reference signal generating circuit 20 to gradually
increase the reference level.
When the reference signal generation circuit 20 receives the instruction to increase gradually,
the DC level of the reference level signal is set to the reference level (DC level, usually power
supply voltage × 0.5) of the audio signal output from the audio processing circuit 9. Gradually
raise up to a).
When the elapsed time from the power-on reaches t4 in FIG. 2, the system control circuit 23
closes the switch 21 (S32 in FIG. 3). The operation confirmation sound signal output from the
confirmation sound generation circuit 10 is added to the reference level signal by the adder 22
and enters the PWM modulation circuit 13 via the switch 11. The PWM modulation circuit 13
PWM modulates the input signal and sends it to the speaker 15 via the inverter 14. As a result,
an operation confirmation sound is output from the speaker 15. When the predetermined time
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has elapsed, the system control circuit 23 opens the switch 21 to stop the output of the
operation confirmation sound (t5 in FIG. 2, S33 in FIG. 3). As a result, the DC level of the signal
entering the speaker 15 is determined by the reference level signal regardless of the presence or
absence of the operation confirmation sound, and there is no abrupt change, so that no pop noise
occurs.
[0029]
When the level of the reference level signal 20a reaches the reference level of the digital audio
signal (step t6 in FIG. 2), the system control circuit 23 connects the switch 11 to the audio
processing circuit 9 side and outputs a digital audio signal (FIG. 3 of S34, S35). Then, it waits for
input of some operation command, such as pressing the operation button from the outside (S36
in FIG. 3). When an operation command is input, the system control unit 23 closes the switch 21
and connects the switch 11 to the adder 22 side so that an operation confirmation sound is
output from the speaker 15 (S37 in FIG. 3). After the predetermined time has elapsed, the switch
11 is connected to the audio processing circuit 9 side, and the output of the operation
confirmation sound is ended (S38 in FIG. 3).
[0030]
As described above, in the first embodiment, when the operation confirmation sound is output, a
reference level signal that gradually changes from the “L” level is generated, and the operation
confirmation sound is added to this signal and output. By doing this, it is possible to suppress an
abrupt change in the signal level at the time of outputting the operation confirmation sound, and
make it possible to output the operation confirmation sound immediately after the power is
turned on without generating a popping noise. Second Embodiment Next, a digital amplifier
circuit according to a second embodiment of the present invention will be described. FIG. 4 is a
block diagram showing a digital amplifier circuit according to a second embodiment of the
present invention, and FIG. 5 is a diagram showing an audio signal output from the digital
amplifier circuit according to the second embodiment.
[0031]
Although the output of the digital amplifier circuit of the second embodiment is a binary signal, it
is shown as a smoothed analog waveform as in FIG. In FIG. 4, reference numeral 31 denotes a
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system control circuit which controls the switch 11, the switch 21 and the reference signal
generation circuit 20. Further, in FIG. 5, reference numeral 51 denotes a reference level signal,
and reference numeral 52 denotes an output of the adder 22.
[0032]
The operation of the digital amplifier circuit of the second embodiment configured as described
above will be described.
[0033]
When the digital amplifier circuit is powered on, the reference signal generation circuit 20
outputs a reference level signal of "L" level.
Also, the system control circuit 31 opens the switch 21, connects the switch 11 to the adder 22,
and outputs a reference level signal to the PWM modulation circuit 13. The PWM modulation
circuit 13 drives the speaker 15 to the “L” level via the inverter 14.
[0034]
Subsequently, the system control circuit 31 sends an instruction to gradually increase the
reference level signal to the reference signal generation circuit 20 (t7 in FIG. 5). When the
reference signal generation circuit 20 receives the gradual increase instruction, as shown at 51
in FIG. 5, the level of the reference level signal is gradually raised. The system control circuit 31
detects that the level of the reference level signal is equal to or greater than the amplitude (b in
FIG. 5) of the operation confirmation sound generated by the confirmation sound generation
circuit 10, and closes the switch 21 (FIG. 5) t8). As a result, the operation confirmation sound is
added to the reference level signal by the adder 22 (52 in FIG. 5), and is output from the speaker
15. The system control circuit 31 opens the switch 21 after a predetermined time has passed and
stops the output of the operation confirmation sound. Furthermore, the system control circuit 31
connects the switch 11 to the audio processing circuit 9 side when the level of the reference level
signal reaches the reference level (DC level, usually power supply voltage x 0.5) of the digital
audio signal. The method of outputting the operation confirmation sound at the time of voice
output is the same as that of the first embodiment.
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[0035]
In the digital amplifier circuit according to the second embodiment, since the operation
confirmation sound is added after the level of the reference level signal becomes equal to or
higher than the amplitude of the operation confirmation sound, the output of the adder 22 is not
higher than the ground level. As a result, it is possible to prevent the occurrence of distortion of
the output waveform that is caused by the above, and it is possible to always output the
operation confirmation sound of the same timbre.
[0036]
In the first embodiment, although the time from the start of the output of the operation
confirmation sound to the stop is set as the predetermined time, the operation is performed by
closing the switch 21 until the switch 11 is switched to the audio processing circuit 9 side. It
does not matter if the confirmation sound continues to be output.
In this case, an audio signal output from the digital amplifier circuit is shown in FIG. In FIG. 6, the
gradual increase of the reference level signal is started at t7, and when the level exceeds b at t8,
the addition and the output of the operation confirmation sound are started. When the reference
level signal reaches the reference level a of the digital audio signal, the output of the operation
confirmation sound is stopped (t9 in FIG. 6). Depending on the amount of change in the reference
level signal during the incremental processing by the reference signal generation circuit 20,
noise may be heard, but by continuing to output the operation confirmation sound while
changing the reference level signal, The noise is concealed, and the discomfort to the user can be
reduced.
[0037]
Third Embodiment Next, a digital amplifier circuit according to a third embodiment of the
present invention will be described. FIG. 7 is a block diagram showing an example of a digital
amplifier circuit according to a third embodiment of the present invention, and FIG. 8 is a
diagram showing an audio signal output from the digital amplifier circuit according to the third
embodiment. Although the output of the digital amplifier circuit according to the third
embodiment is a binary signal, it is shown as a smoothed analog waveform as in FIG.
[0038]
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In FIG. 7, reference numeral 41 denotes a confirmation sound generation circuit that generates
an operation confirmation sound, and reference numeral 42 denotes a system control circuit that
controls the switch 11, the switch 21, and the confirmation sound generation circuit 41. In FIG.
8, reference numeral 81 denotes a reference level signal, and reference numeral 82 denotes an
output of the adder 22.
[0039]
The operation of the digital amplifier circuit of the third embodiment configured as described
above will be described. When the digital amplifier circuit of the third embodiment is powered
on, the reference signal generation circuit 20 outputs a reference level signal whose signal for
driving the speaker 15 corresponds to the “L” level. The system control circuit 42 also
connects the switch 11 to the adder 21 side. Further, the system control circuit 42 sets the
confirmation sound generation circuit 41 so that the amplitude of the operation confirmation
sound generated is equal to the level of the reference level signal (c in FIG. 8). Then, the switch
21 is closed, and the operation confirmation sound output from the confirmation sound
generation circuit 41 is added to the reference level signal. Next, a gradual increase command is
sent to the reference signal generation circuit 20 to start gradual increase of the reference level
signal (t7 in FIG. 8). The amplitude of the operation confirmation sound increases in conjunction
with the level of the reference level signal, and when the desired amplitude (b in FIG. 7) is
reached, the system control circuit 42 stops changing in amplitude. The subsequent operation is
the same as that of the second embodiment and will not be described.
[0040]
In the digital amplifier circuit according to the third embodiment, distortion of the waveform due
to the output amplitude falling below the “L” level when outputting the operation confirmation
sound immediately after the start of the gradual increase of the reference level signal, and
abnormal noise It can prevent the occurrence.
[0041]
In the above description, although the operation confirmation sound is described as a rectangular
wave, it may be a sine wave or another waveform.
[0042]
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Further, in the second embodiment, the method of continuing the operation confirmation sound
while the reference level signal is changed has been described. However, this method can be
applied to the first or third embodiment. is there.
[0043]
In the third embodiment, the amplitude of the operation confirmation sound is the same as the
level of the reference level signal. However, any level may be set as long as it is equal to or lower
than the level of the reference level signal.
For example, by gradually raising the amplitude, it is possible to realize an operation
confirmation sound that is pleasant to the user.
[0044]
In the above description, although the configuration realized by diverting the conventional
confirmation sound generation circuit is described, a confirmation sound generation circuit is
separately added, and the switch 11 of FIG. 10 is configured as a 3-input 1-output type. It can
also be done.
[0045]
Further, in the above description, the processing performed by the audio processing circuit 9 is
assumed to be oversampling processing and noise shaping processing, and after these
processings, the signal subjected to these processing and the signal including the operation
confirmation sound are Although the changeover switch for switching is provided, if the DC level
of the operation confirmation sound is configured to change continuously with the signal before
and after in time, digital before the oversampling process or the noise shape process A switch
may be provided to switch between the audio signal system signal and the output of the adder
22.
[0046]
The digital amplifier circuit according to the present invention is an electronic device such as a
car stereo or portable compact disc player, in which the user may operate without looking
directly at the device body, the user may press the operation button. It is a circuit for outputting
an operation confirmation sound to be transmitted, a so-called beep sound, and is useful when
applied to a portable electronic device.
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[0047]
Block diagram of digital amplifier circuit according to Embodiment 1 of the present invention
Diagram showing audio signal outputted by digital amplifier circuit according to Embodiment 1
of the present invention Flow chart of processing performed by system control circuit 23 in
Embodiment 1 of the present invention A block diagram of a digital amplifier circuit according to
a second embodiment of the present invention. A diagram showing an audio signal output from a
digital amplifier circuit according to a second embodiment of the present invention. A second
output from a digital amplifier circuit according to a second embodiment of the present
invention. A diagram showing an audio signal. A block diagram of a digital amplifier circuit
according to a third embodiment of the present invention. A diagram showing an audio signal
output from a digital amplifier circuit according to a third embodiment of the present invention.
A block diagram of a conventional operation confirmation sound output circuit Block diagram of
a conventional digital amplifier circuit having a sound output function Audio signal output from a
conventional digital amplifier circuit Diagram showing the
Explanation of sign
[0048]
1-2: Amplifier 3: Microcomputer chip 4, 6: Resistor 5: Capacitor 7: Volume control circuit 9:
Audio processing circuit 10, 41: Confirmation sound generation circuit 11, 21: Switch 12, 23, 31,
42: System control Circuit 13: PWM conversion circuit 14: inverter 15: speaker 20: reference
signal generation circuit 22: adder 51, 81: reference level signal 52, 82: output of adder 22
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