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JP2013005215

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DESCRIPTION JP2013005215
Abstract: To provide an audio signal transmission system capable of transmitting an audio signal
with a simple configuration. An analog-to-digital converter 15 converts an analog voice signal
into a digital voice signal and outputs the digital voice signal, and converts a digital voice signal
output from the analog-digital converter 15 into an analog voice signal and outputs the same.
The analog-to-digital converter 15 includes a comparator 18 and an integrator 17. The oscillation
circuit 16 is configured by the comparator 18 and the integrator 17, so that an analog audio
signal is converted to the analog signal. The digital-to-analog converter has a low-pass filter
circuit that converts a digital audio signal into an analog audio signal, which converts the digital
audio signal into a digital audio signal whose pulse width changes according to the audio signal.
[Selected figure] Figure 1
Voice signal transmission system
[0001]
The present invention relates to an audio signal transmission system.
[0002]
In order to transmit an analog voice signal over a long distance, a coaxial cable or the like is used
to suppress external noise.
If the transmission distance is relatively short, use a long speaker cable to transmit and output
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1
analog audio signals to the speakers. When transmitting analog audio signals from one audio
input device to multiple audio output devices (speakers, etc.), multiple cables are used, one for
each audio output device.
[0003]
Therefore, wiring many coaxial cables from the amplifier output of the voice input device, or
routing many speaker cables over a long distance like a bundle takes a lot of time and labor. For
example, when announcing from several speakers as in a station broadcast, many coaxial cables
are drawn from the broadcasting equipment and each one is wired to each speaker amplifier, so
the amount of wiring is large. It takes time and effort for wiring. In addition, when there is an
abnormality, it is necessary to find out which wiring has an abnormality, and it takes time for
management.
[0004]
Unexamined-Japanese-Patent No. 5-14297
[0005]
Therefore, it is conceivable to digitize and transmit an analog voice signal (see, for example,
Patent Document 1), but the use of a dedicated analog-to-digital converter complicates the circuit
and increases the cost of electronic components and electronic components. It was also
necessary to use electronic devices and the like.
[0006]
The present invention has been made in view of such problems, and it is an object of the present
invention to provide an audio signal transmission system capable of transmitting an audio signal
with a simple configuration.
[0007]
In order to achieve such an object, an audio signal transmission system according to the present
invention comprises an analog-to-digital converter for converting an analog audio signal into a
digital audio signal and outputting the digital audio signal, and the above-mentioned output from
the analog-to-digital converter. A digital to analog converter for converting a digital audio signal
into the analog audio signal and outputting the analog audio signal, the analog to digital
converter including a comparator and an integrator, the comparator and the integrator The
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2
oscillation circuit is configured to convert the analog voice signal into the digital voice signal
whose pulse width changes in accordance with the analog voice signal, and the digital-to-analog
converter converts the digital voice signal into the analog voice signal. It has a low pass filter
circuit that converts it into a voice signal.
[0008]
In the above-mentioned invention, it is preferable to configure the oscillation circuit by
electrically connecting the integrator between the output terminal of the comparator and the
positive phase input terminal.
[0009]
In the above invention, when a plurality of the digital-to-analog converters are provided,
transmission is performed to transmit the digital audio signals output from the analog-to-digital
converters to the plurality of digital-to-analog converters, respectively. It is preferable to include
a means (for example, the output circuit 19 in the embodiment).
[0010]
According to the present invention, by configuring the oscillator circuit with the comparator and
the integrator, the analog voice signal is converted into a digital voice signal whose pulse width
changes in accordance with the analog voice signal. It can be converted into an analog voice
signal, and it becomes possible to transmit the voice signal with a simple configuration.
[0011]
An integrator is electrically connected between the output terminal of the comparator and the
positive phase input terminal to form an oscillation circuit, thereby converting an analog audio
signal into a digital audio signal with a simple circuit configuration. be able to.
[0012]
In addition, by providing transmission means for respectively transmitting digital audio signals
output from the analog-to-digital converter to the plurality of digital-to-analog converters, analog
communication can be performed using existing communication standards (for example, RS-485
etc.) The same digital voice signal output from the digital converter can be simultaneously
transmitted to a plurality of digital to analog converters.
[0013]
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It is a circuit diagram of an oscillation circuit.
It is a system configuration figure of a voice signal transmission system.
It is a block diagram of a voice input device.
It is a graph which shows the change of an integrator output in the state without an input signal,
and a comparator output.
It is a graph which shows a change of an integrator output in the state where a positive input
signal is inputted, and a comparator output.
It is a graph which shows a change of an integrator output and a comparator output in the state
where a negative input signal is inputted.
It is a graph which shows the change of the digital signal with respect to the change of an input
analog signal.
It is a block diagram of an audio output device.
It is a circuit diagram of a low pass filter circuit.
It is a graph which shows the change of the analog signal with respect to the change of an input
digital signal.
[0014]
Hereinafter, preferred embodiments of the present invention will be described with reference to
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the drawings. An audio signal transmission system 1 according to the present embodiment is
shown in FIG. The audio signal transmission system 1 is a transmission cable for electrically
connecting one audio input device 10, a plurality of audio output devices 20A to 20D, and the
audio input devices 10 to the audio output devices 20A to 20D. And 30 are configured. Although
FIG. 2 shows the first audio output device 20A, the second audio output device 20B, the third
audio output device 20C, and the fourth audio output device 20D as the plurality of audio output
devices, the present invention is limited thereto. You can use more or less audio output devices
than this.
[0015]
As shown in FIG. 3, the voice input device 10 exemplifies the microphone 11 as a device for
inputting a voice signal from the outside, but the microphone 11 may be replaced with another
voice signal input device. And an amplifier 12 to which an audio signal is input from the
microphone 11, an analog-to-digital converter 15 electrically connected to the amplifier 12, and
an output circuit 19 electrically connected to the transmission cable 30. And be configured. The
microphone 11 converts and amplifies voice (sound wave) into an electrical signal (analog voice
signal) and outputs the signal to the amplifier 12. The amplifier 12 amplifies the analog voice
signal input from the microphone 11 to the required size of the electrical signal and outputs the
amplified signal to the analog-to-digital converter 15. The analog-to-digital converter 15 converts
an analog voice signal input from the amplifier 12 into a digital voice signal and outputs the
digital voice signal to the output circuit 19. The output circuit 19 is configured using electronic
components such as IC (Integrated Circuit), and the digital audio signal output from the analogto-digital converter 15 is converted into each audio according to a predetermined communication
standard (for example, RS-485). Transmit (output) to the output devices 20A to 20D.
[0016]
Note that, as a predetermined communication standard, for example, RS-485, which is a
communication standard that supports bus-type multipoint connection and that allows
connection of a plurality of pairs, is a communication standard that supports a pair of multidrop
connections. A certain RS-422 or the like is used. Thus, the digital audio signal output from the
output circuit 19 of the audio input device 10 is transmitted to the audio output devices 20A to
20D through the transmission cable 30, respectively.
[0017]
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5
By the way, as shown in FIG. 1, the analog-to-digital converter 15 is connected in series with a
first input-side capacitor Cc1 whose one terminal is connected to the amplifier 12 and a first
input-side capacitor Cc1. It comprises an input side resistor Ri and an oscillation circuit 16
connected in series with the input side resistor Ri. The first input-side capacitor Cc1 removes the
DC (direct current) component of the analog audio signal input from the amplifier 12 and affects
the bias potential of the circuit when the circuit is configured with a single power supply. In
order not to be present, only AC (alternating current) components are combined. As a result, it is
possible to remove low frequency components and oscillate only the signal change of the analog
audio signal, which does not require accuracy stabilization as in the conventional analog-todigital converter which makes the reference voltage very stable. It can be input to the circuit 16.
[0018]
The input-side resistor Ri determines the magnitude of the current for changing (that is,
modulating) the current flowing to the integrator 17 of the oscillation circuit 16 according to the
analog audio signal. In the present embodiment, the input voltage of the analog audio signal
input to the analog-to-digital converter 15 is Vi, and the current flowing through the input-side
resistor Ri is Ii.
[0019]
The oscillation circuit 16 is configured to include an integrator 17, a comparator 18, and two
oscillation resistors Rc1 and Rc2. Further, the integrator (integrating circuit) 17 is configured to
include an integrating operational amplifier Uf, an integrating resistor Rf, and an integrating
capacitor Cf. The reference voltage Vо is input to the positive phase input terminal (+ input
terminal) of the integrating operational amplifier Uf. The reference voltage Vо is 1/2 of the
power supply voltage in the case of one power supply, and is the ground voltage in the case of
both power supplies. One terminal of the integrating resistor Rf, one terminal of the integrating
capacitor Cf, and the terminal of the input-side resistor Ri are connected to the negative phase
input terminal (-input terminal) of the integrating operation amplifier Uf . The output terminal of
the integrating operational amplifier Uf is connected to the positive phase input terminal of the
comparator 18 via the first oscillation resistor Rc1. The other terminal of the integrating
capacitor Cf is connected to the connection point between the output terminal of the integrating
operational amplifier Uf and one terminal of the first oscillation resistor Rc1.
09-05-2019
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[0020]
The reference voltage Vо is input to the negative phase input terminal (− input terminal) of the
comparator 18. The reference voltage Vо is the same as that input to the integrating operational
amplifier Uf. The positive phase input terminal (+ input terminal) of the comparator 18 is
connected to the output terminal of the integrating operational amplifier Uf via the first
oscillation resistor Rc1 as described above, but the positive phase of the comparator 18 is One
terminal of a second oscillation resistor Rc2 is connected to a connection point between the input
terminal and the other terminal of the first oscillation resistor Rc1. The other terminal of the
second oscillation resistor Rc 2 and the other terminal of the integration resistor Rf are
connected to the output terminal of the comparator 18. Thus, the integrator 17 is electrically
connected between the output terminal of the comparator 18 and the positive phase input
terminal. The output terminal of the comparator 18 is connected to the output circuit 19.
[0021]
In such an oscillation circuit 16, the output voltage Vs of the integrator 17 and the output
voltage Vd of the comparator 18 are divided by the resistance ratio of the first oscillation resistor
Rc1 and the second oscillation resistor Rc2, and the comparison is performed. Input to the
positive phase input terminal of the Then, when the input voltage to the comparator 18 reaches
the reference voltage V о, the output voltage V d of the comparator 18 is (high or low) inverted
so that the operation of the integrator 17 is in the reverse direction so that the circuit oscillates.
It has become. As described above, the oscillator circuit 16 can be easily configured by the
commercially available inexpensive operational amplifier (the integrating operational amplifier
Uf) and the comparator 18. In addition, since the stability of the oscillation circuit 16 does not
have to affect the analog voice signal, it is not necessary to obtain high stability with expensive
circuit components.
[0022]
The resistance ratio between the first oscillation resistor Rc1 and the second oscillation resistor
Rc2 is such that the input voltage of the comparator 18 reaches the reference voltage Vо before
the output voltage Vs of the integrator 17 saturates. It is set. At this time, the resistance value of
the first oscillation resistor Rc1 normally becomes smaller than the resistance value of the
second oscillation resistor Rc2 so that the output voltage Vs of the integrator 17 can oscillate
09-05-2019
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stably within the power supply voltage. Is set as
[0023]
Next, the operation of the oscillation circuit 16 will be described with reference to FIGS. FIG. 4
shows the change of the output voltage Vs of the integrator 17 and the change of the output
voltage Vd of the comparator 18 in the absence of the input signal (input voltage Vi). When only
the AC component of the input voltage Vi with respect to the reference voltage V0 is considered
as shown in FIG. 4, it can be treated as one without the first input-side capacitor Cc1.
[0024]
First, the time when the output voltage Vd of the comparator 18 becomes a high (high) voltage
state (time a in FIG. 4) will be described. Since the output voltage Vd of the comparator 18 is a
high voltage, a current (this current is conveniently referred to as a positive direction current If)
flows from the comparator 18 through the integration resistor Rf. Since the positive direction
current If flows to the integrator 17, the integration capacitor Cf is charged as the integrated
current Ic = If when the analog voice signal is not input. Therefore, the output voltage Vs of the
integrator 17 gradually decreases in proportion to the charging by the integral current Ic. For
example, assuming that the capacitance of the integration capacitor Cf is Cf and the resistance
value of the integration resistor Rf is Rf, in the case of both power supplies (reference voltage Vo
= 0), when the input current Ii = 0, Vs = It becomes-(1 / Cf) * (Vd / Rf) * dt.
[0025]
As described above, the output voltage Vs of the integrator 17 and the output voltage Vd of the
comparator 18 are divided by the resistance ratio of the first oscillation resistor Rc1 and the
second oscillation resistor Rc2, Input to the positive phase input terminal. Then, when the input
voltage to the comparator 18 becomes lower than the reference voltage Vо (point b in FIG. 4),
the output voltage Vd of the comparator 18 switches from high (high) voltage to low (low)
voltage.
[0026]
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At this time, since the output voltage Vd of the comparator 18 is a low voltage, a current in the
reverse direction to that of the high voltage (this current is conveniently referred to as a reverse
current -If) flows via the integrating resistor Rf. . Then, since the integral current Ic is also a
current in the opposite direction to the case of the high voltage, when there is no input of the
analog voice signal, the capacitor Cf for integration is discharged as the integral current Ic = −If.
Therefore, the output voltage Vs of the integrator 17 gradually rises in proportion to the
discharge by the integrating capacitor Cf. Then, when the input voltage to the comparator 18
becomes higher than the reference voltage Vо (point c in FIG. 4), the output voltage Vd of the
comparator 18 switches from low voltage to high voltage.
[0027]
Similarly, at time points d, e, f, ... in FIG. 4, the output voltage Vd of the comparator 18 is inverted
(high and low) and the operation of the integrator 17 is reversed, whereby the oscillation is
continued. . In this way, it is possible to obtain a digital audio signal in which the output voltage
Vd of the comparator 18 is in the form of a rectangular pulse corresponding to a state where
there is no input of an analog audio signal. Even when the output voltage Vd of the comparator
18 is a bipolar voltage, there is no large fluctuation of the oscillation frequency, so that it is
possible to easily transmit the digital audio signal to the output circuit 19 by capacitor coupling.
[0028]
FIG. 5 shows the change of the output voltage Vs of the integrator 17 and the change of the
output voltage Vd of the comparator 18 (solid line) when the input signal of the positive voltage
is inputted. Further, the change in the output voltage Vs of the integrator 17 and the change in
the output voltage Vd of the comparator 18 in the absence of an input signal are indicated by
broken lines. When only the AC component of the input voltage Vi with respect to the reference
voltage Vо is considered as shown in FIG. 5, it can be treated as the one without the first inputside capacitor Cc1.
[0029]
First, the time point when the output voltage Vd of the comparator 18 becomes a low (low)
voltage state (point b in FIG. 5) will be described. Since the output voltage Vd of the comparator
09-05-2019
9
18 is a low voltage, a reverse current -If flows through the integrating resistor Rf. When the
analog voice signal is a positive voltage, the input current Ii (in the positive direction) flows in the
integrator (integral circuit) 17, and the integration capacitor Cf is discharged as the integral
current Ic = (− If + Ii). Therefore, the output voltage Vs of the integrator 17 has an absolute
value of the integral current Ic smaller by the amount of the input current Ii, so the output
voltage Vs is slower in proportion to the discharge by the integration capacitor Cf than in the
case where there is no input Rise at a steady rate of change. Then, when the input voltage to the
comparator 18 becomes higher than the reference voltage Vо (point c ′ in FIG. 5), the output
voltage Vd of the comparator 18 switches from low (low) voltage to high (high) voltage Wow.
[0030]
At this time, since the output voltage Vd of the comparator 18 is a high voltage, the forward
current If flows from the comparator 18 via the integrating resistor Rf. When the analog voice
signal is a positive voltage, the input current Ii (in the positive direction) flows in the integrator
(integrating circuit) 17, so that the integration capacitor Cf is charged with the integration
current Ic = (If + Ii). Therefore, the output voltage Vs of the integrator 17 has a larger absolute
value of the integral current Ic by the amount of the input current Ii, so it is steeper in proportion
to charging by the integral current Ic than when there is no input of an analog audio signal.
Decrease at the rate of change. Then, when the input voltage to the comparator 18 becomes
lower than the reference voltage V0 (point d in FIG. 5), the output voltage Vd of the comparator
18 switches from high (high) voltage to low (low) voltage.
[0031]
Similarly, the output voltage Vd of the comparator 18 is inverted (high and low) to cause the
operation of the integrator 17 to be in the reverse direction, whereby the oscillation is continued.
In this manner, it is possible to obtain a digital audio signal in which the output voltage Vd of the
comparator 18 is in the form of a rectangular pulse corresponding to the case where an input
signal of a positive voltage is input as an analog audio signal. Since the value of the input current
Ii is the same regardless of the charge and discharge in the integration capacitor Cf, the input
current Ii acts in the opposite direction when the direction of the integral current Ic is reversed.
Therefore, the period of the digital audio signal when the positive voltage input signal is input as
the analog audio signal is the same as that when the analog audio signal is not input, and the
comparator 18 is selected according to the value of the input current Ii. The period ratio of the
high (high) voltage to the low (low) voltage of the output voltage Vd, that is, the pulse duty ratio
changes. In the example of FIG. 5, when an input signal of a positive voltage is input as an analog
09-05-2019
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audio signal, the output voltage Vd of the comparator 18 is changed from a low voltage to a high
voltage as compared with the case where no analog audio signal is input. As the time of switching
changes from c to c ', the period of the low voltage becomes longer and the period of the high
voltage becomes shorter.
[0032]
FIG. 6 shows the change of the output voltage Vs of the integrator 17 and the change of the
output voltage Vd of the comparator 18 (solid line) when the input signal of the negative voltage
is input. Further, the change in the output voltage Vs of the integrator 17 and the change in the
output voltage Vd of the comparator 18 in the absence of an input signal are indicated by broken
lines. When only the AC component of the input voltage Vi with respect to the reference voltage
Vо is considered as shown in FIG. 6, it can be treated as the one without the first input-side
capacitor Cc1.
[0033]
First, the time point when the output voltage Vd of the comparator 18 is in the low (low) voltage
state (time d in FIG. 6) will be described. Since the output voltage Vd of the comparator 18 is a
low voltage, a reverse current -If flows through the integrating resistor Rf. When the analog voice
signal is a negative voltage, an input current −Ii in the reverse direction to that of the positive
voltage flows in the integrator (integral circuit) 17. Therefore, the integration capacitor Cf is
obtained as an integral current Ic = (− If−Ii). Is discharged. Therefore, the output voltage Vs of
the integrator 17 has an absolute value of the integral current Ic larger by the amount of the
input current -Ii, so that there is no input of the analog audio signal in proportion to the
discharge by the integrating capacitor Cf. It also rises at a rapid rate of change. Then, when the
input voltage to the comparator 18 becomes higher than the reference voltage Vо (time e ′ ′
in FIG. 6), the output voltage Vd of the comparator 18 changes from low (low) voltage to high
(high) voltage. Switch.
[0034]
At this time, since the output voltage Vd of the comparator 18 is a high voltage, the forward
current If flows from the comparator 18 via the integrating resistor Rf. When the analog voice
signal is a negative voltage, an input current −Ii in the reverse direction to that of the positive
09-05-2019
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voltage flows in the integrator (integrator circuit) 17. Therefore, the integration capacitor Cf is
charged as an integral current Ic = (If−Ii). Be done. Therefore, the output voltage Vs of the
integrator 17 is smaller in absolute value of the integral current Ic by the amount of the input
current -Ii, so that the output voltage Vs is more gradual in proportion to charging by the integral
current Ic Rate of change. Then, when the input voltage to the comparator 18 becomes lower
than the reference voltage Vо (point f in FIG. 6), the output voltage Vd of the comparator 18
changes from high (high) voltage to low (low) voltage. Switch.
[0035]
Similarly, the output voltage Vd of the comparator 18 is inverted (high and low) to cause the
operation of the integrator 17 to be in the reverse direction, whereby the oscillation is continued.
In this manner, it is possible to obtain a digital audio signal in which the output voltage Vd of the
comparator 18 is in the form of a rectangular pulse corresponding to the case where an input
signal of negative voltage is input as an analog audio signal. Since the value of the input current Ii in the reverse direction is the same as in the case of the positive voltage regardless of the
charge and discharge in the integrating capacitor Cf, the input current -Ii is reversed when the
direction of the integrated current Ic is reversed. Act in the direction. Therefore, the period of the
digital audio signal when the negative voltage input signal is input as the analog audio signal is
the same as that when the analog audio signal is not input, and the input current in the reverse
direction to that of the positive voltage. Depending on the value of Ii, the period ratio of the high
(high) voltage to the low (low) voltage of the output voltage Vd of the comparator 18, that is, the
duty ratio of the pulse changes. In the example of FIG. 6, when an input signal of negative voltage
is input as an analog audio signal, the time when the output voltage Vd of the comparator 18
switches from low voltage to high voltage as compared with the case where no analog audio
signal is input. As the voltage changes from e to e ′ ′, the period of the high voltage becomes
longer and the period of the low voltage becomes shorter.
[0036]
In the description of the operation of the oscillation circuit 16, the direction in which the current
is supplied from one direction is uniquely determined and described. Therefore, defining the
current direction in the opposite direction, the integrating capacitor Cf is charged when the
reverse current flows. Thus, the opposite of charge is defined as discharge, and for convenience,
one of charge and discharge is defined and explained. Further, the low (low) voltage of the
comparator 18 is not limited to the low (low) voltage of the output circuit 19. Depending on the
definition of the interface, it may be defined as either high voltage or low voltage.
09-05-2019
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[0037]
As can be understood from the above description, the change of the input waveform of the
analog audio signal is the change of the pulse width ratio (duty ratio) of the digital audio signal.
FIG. 7 shows that the change of the input signal (input voltage Vi), which is an analog voice
signal, has a period width of high (high) voltage and low (low) voltage in the digital voice signal
(output voltage Vd of the comparator 18). It shows that it can be replaced by change. The
oscillation frequency (carrier frequency) of the digital audio signal is a frequency (several 100
kHz) sufficiently higher than the frequency (several kHz to 10 kHz) of the analog audio signal.
Therefore, the actual frequency of the digital audio signal shown in FIG. The waveform has more
repetitions than the input waveform of the analog audio signal. The oscillation frequency of the
digital audio signal is determined by the output voltage Vd of the comparator 18, the reference
voltage Vо, the resistance value of the first oscillation resistor Rc1, the resistance value of the
second oscillation resistor Rc2, and the integration capacitor Cf. And the resistance value of the
integrating resistor Rf.
[0038]
When the pulse width ratio (duty ratio) of the digital audio signal changes, the DC (direct current)
component of the digital audio signal changes. The DC component of the digital audio signal can
be detected by integrating the digital audio signal. Note that integration of the digital audio signal
corresponds to extracting low frequency components from the digital audio signal. Therefore, in
order to reproduce an analog voice signal from a digital voice signal, the digital voice signal may
be integrated, that is, low frequency components may be extracted from the digital voice signal
by a low pass filter. If there is a sufficient difference between the frequency of the analog audio
signal and the oscillation frequency (carrier frequency) of the digital audio signal, the low
frequency component of the digital audio signal can be separated by a simple low pass filter. In
addition, since a simple low-pass filter can be easily configured using a general-purpose
operational amplifier IC, the low-pass filter of the required order (number of stages) can be used
to easily separate the analog audio signal at low cost. It is possible to play). Therefore, low-pass
filter circuits are provided as digital-to-analog converters in each of the voice output devices 20A
to 20D.
[0039]
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13
Each of the audio output devices 20A to 20D has the same configuration. Therefore, in the
present embodiment, only the first audio output device 20A will be described, and the
descriptions of the other audio output devices 20B to 20D will be omitted. As shown in FIG. 8,
the first audio output device 20A includes an input circuit 21 electrically connected to the
transmission cable 30, and a digital / analog converter 22 electrically connected to the input
circuit 21. A drive circuit 26 electrically connected to the digital / analog converter 22 and a
speaker 27 electrically connected to the drive circuit 26 (the speaker 27 is illustrated as a device
for processing an audio signal, 27 may be replaced with another audio signal processing device).
[0040]
The input circuit 21 is configured using electronic components such as IC (Integrated Circuit),
and is a digital audio signal transmitted from the output circuit 19 of the audio input device 10
according to a predetermined communication standard (for example, RS-485). Are output to the
digital-to-analog converter 22. The digital / analog converter 22 converts the digital audio signal
input from the input circuit 21 into an analog audio signal and outputs the analog audio signal to
the drive circuit 26. The drive circuit 26 is an amplifier for amplifying an analog audio signal,
amplifies the analog audio signal input from the digital / analog converter 22, and outputs the
amplified analog audio signal to the speaker 27. The speaker 27 converts the electrical signal
(analog voice signal) input from the drive circuit 26 into mechanical vibration of the membrane
to produce sound, and outputs the voice input to the microphone 11 of the voice input device 10.
[0041]
By the way, as shown in FIG. 9, the digital-to-analog converter 22 is connected in series with a
second input-side capacitor Cc2 whose one terminal is connected to the input circuit 21 and a
second input-side capacitor Cc2. The low pass filter circuit 23 and the output side capacitor Cc3
connected in series with the low pass filter circuit 23 are configured. When there is a potential
difference between the input circuit 21 and the low-pass filter circuit 23, the second input-side
capacitor Cc2 eliminates DC (direct current) potential difference as coupling of only AC (AC)
component. Further, when there is a potential difference between the low pass filter circuit 23
and the drive circuit 26, the output-side capacitor Cc3 eliminates DC (direct current) potential
difference as coupling of only AC (AC) component. The second input capacitor Cc2 and the
output capacitor Cc3 may not be provided if not necessary.
09-05-2019
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[0042]
The low pass filter circuit 23 comprises, for example, a first low pass filter circuit 24 and a
second low pass filter circuit 25 connected in series with the first low pass filter circuit 24 to
form a fourth-order low pass filter. The first low pass filter circuit 24 is a multiple feedback low
pass filter, and includes a first operational amplifier U1, three resistors R1 to R3, and two
capacitors C1 to C2. The reference voltage Vо is input to the positive phase input terminal (+
input terminal) of the first operational amplifier U1. The reference voltage Vо is 1/2 of the
power supply voltage in the case of one power supply, and is the ground voltage in the case of
both power supplies. The negative phase input terminal (− input terminal) of the first
operational amplifier U1 is connected to the second input capacitor Cc2 (that is, the input circuit
21) via the first resistor R1 and the second resistor R2. Ru. The output terminal of the first
operational amplifier U1 is connected to the second low pass filter circuit 25.
[0043]
One terminal of a third resistor R3 is connected to a connection point between the first resistor
R1 and the second resistor R2, and the other terminal of the third resistor R3 is connected to the
output terminal of the first operational amplifier U1. Connected Further, one terminal of the first
capacitor C1 is connected to a connection point of the first resistor R1 and the second resistor
R2, and the other terminal of the first capacitor C1 is grounded. One terminal of a second
capacitor C2 is connected to a connection point between the reverse phase input terminal of the
first operational amplifier U1 and the second resistor R2, and the other terminal of the second
capacitor C2 is a first operational amplifier U1. Connected to the output terminal of
[0044]
The second low pass filter circuit 25 is a multiple feedback type low pass filter, and includes a
second operational amplifier U2, three resistors R4 to R6, and two capacitors C3 to C4. The
reference voltage Vо is input to the positive phase input terminal (+ input terminal) of the
second operational amplifier U2. The reference voltage Vо is set as in the case of the first
operational amplifier U1. The negative phase input terminal (-input terminal) of the second
operational amplifier U2 is connected to the first low pass filter circuit 24 (that is, the output
terminal of the first operational amplifier U1) via the fourth resistor R4 and the fifth resistor R5.
Connected with The output terminal of the second operational amplifier U2 is connected to the
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output-side capacitor Cc3 (ie, the drive circuit 26).
[0045]
One terminal of a sixth resistor R6 is connected to the connection point between the fourth
resistor R4 and the fifth resistor R5, and the other terminal of the sixth resistor R6 is connected
to the output terminal of the second operational amplifier U2. Connected Further, one terminal of
the third capacitor C3 is connected to a connection point of the fourth resistor R4 and the fifth
resistor R5, and the other terminal of the third capacitor C3 is grounded. One terminal of a fourth
capacitor C4 is connected to a connection point between the reverse phase input terminal of the
second operational amplifier U2 and the fifth resistor R5, and the other terminal of the fourth
capacitor C4 is a second operational amplifier U2 Connected to the output terminal of
[0046]
The high frequency component including the oscillation frequency (carrier frequency) of the
digital audio signal is attenuated by the low pass filter circuit 23 as described above, and the low
frequency component including the audio frequency is passed and input from the input circuit
21. The digital audio signal can be converted to an analog audio signal and reproduced. FIG. 10
shows a change in the output voltage Vf of the low pass filter circuit 23 when the output voltage
Vd of the oscillation circuit 16 (comparator 18) is input as a digital audio signal. From FIG. 10, it
can be seen that the change of the duty ratio of the digital audio signal becomes the change of
the DC potential and is reproduced as the change of the voltage of the analog audio signal. As
described above, since the oscillation frequency (carrier frequency) of the digital audio signal is a
frequency (several 100 kHz) sufficiently higher than the frequency (several kHz to 10 kHz) of the
analog audio signal, the digital shown in FIG. The actual waveform of the audio signal has an
even greater number of repetitions as compared to the output waveform of the analog audio
signal.
[0047]
As described above, according to the present embodiment, by configuring the oscillation circuit
16 with the comparator 18 and the integrator 17, the pulse width (duty ratio) of the analog audio
signal changes in accordance with the analog audio signal. In order to convert into a digital audio
signal, it is possible to convert into an analog audio signal by a simple oscillation circuit, and it
becomes possible to transmit an audio signal with a simple configuration.
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16
[0048]
Note that the integrator 17 is electrically connected between the output terminal of the
comparator 18 and the positive phase input terminal to constitute the oscillation circuit 16,
whereby the analog audio signal is converted to a digital audio signal with a simple circuit
configuration. It can be converted to a signal.
[0049]
Also, by providing an output circuit 19 for transmitting digital audio signals output from the
analog-to-digital converter 15 of the audio input device 10 to the digital-to-analog converters 22
of the plurality of audio output devices 20A to 20D, respectively. The same digital audio signal
output from the analog-to-digital converter 15 can be simultaneously transmitted to a plurality of
digital-to-analog converters 22 using a communication standard (e.g., RS-485).
[0050]
Although the microphone 11 is connected to the amplifier 12 in the above embodiment, the
present invention is not limited to this, and may be configured to receive an analog audio signal
from an external amplifier.
[0051]
Further, in the above embodiment, the speaker 27 is connected to the drive circuit 26. However,
the present invention is not limited to this, and the amplifier of the drive circuit 26 is not limited
to the analog audio signal reproduced by the digital to analog converter 22. It may be configured
to output to a separate audio signal processing device.
[0052]
Further, in the above-described embodiment, a plurality of audio output devices 20A to 20D
(digital to analog converter 22) are electrically connected to one audio input device 10 (analog to
digital converter 15). However, the present invention is not limited to this, using existing
communication standards (RS-485), multiple voice input devices (analog to digital converters),
multiple voice output devices (digital to analog converters) and electricity Connection is also
possible.
[0053]
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Further, although the fourth-order low-pass filter is configured in the above-described
embodiment, the present invention is not limited to this.
The order of the low-pass filter is determined by the ability to separate and suppress the analog
voice signal and the carrier digital signal (specifically, the ratio of suppression of the carrier
frequency to the voice frequency), and if necessary, the order may be higher than the fourth
order. High (or low) low-pass filter can be configured.
[0054]
DESCRIPTION OF SYMBOLS 1 voice signal transmission system 10 voice input device 15 analogto-digital converter 16 oscillation circuit 17 integrator 18 comparator 19 output circuit 20 voice
output device 21 input circuit 22 digital-analog converter 23 low pass filter circuit 30
transmission cable
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