JPS62133848A - Voice transmission circuit - Google Patents

Abstract

PURPOSE:To suppress feeling of unpleasantness due to noises of a sent voice by discriminating whether an input signal fed from a microphone is a voice or a noise, generating a level output in response to the noise level and adjusting the level of the input signal in response to the level output. CONSTITUTION:The voice at the transmission side and the surrounding noise enter the microphone 4 of a handset 2 and is fed to a transmission system 6. The signal fed to the system 6 is fed to an attenuator 34 and to a signal discriminating circuit 10, which discriminates whether the input signal is a voice or a noise and generates a level output in response to the noise level and gives it to the circuit 34. A comparator 24 compares the signal level between reception systems 6 and 16 and gives an output to a changeover control circuit 26 installed as a talking mode changeover means. The circuit 26 uses the discrimination output from the circuit 10 to apply transmission/reception changeover when a voice exists in the signal of the system 6 and generates a control outputs to prevent malfunction due to noises. Thus, the feeling of unpleasantness due to noises of the sent voice is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voice transmission circuit suitable for a signal system of a telephone device, and more particularly to prevention of deterioration in intelligibility due to noise.

[Conventional technology]

Conventionally, speakerphones and interphones have been installed on a tabletop with a handset that combines a microphone and a speaker, allowing the caller to send and receive calls without having to pick up the handset. telephone devices have been proposed.

FIG. 4 shows an example of such a telephone device.

The input signal applied to the microphone 4 of the handset 2 is applied to a current control amplifier (CCA) 8 installed in the transmission system 6 as a signal passing/blocking means, and also to a signal discrimination circuit for discriminating whether it is voice or noise. It has been added to 10.

In this case, the microphone 4 receives the voice representing the message to be sent to the other party and the surrounding noise of the location where the handset 2 is installed, and the input signal from the microphone 4 to the transmission line 6 includes the voice. Both components and noise components are included.

Further, the voice signal sent from the telephone line 12 is received by a signal transmission/reception circuit 14, and is applied from this signal transmission/reception circuit 14 to a current control amplifier (OCA) 18 installed as a signal passage/blocking means in a reception line 16. .

If this telephone device is now set to talk mode and the CC
Assuming that A3 is outputting an audio signal, this audio signal and the audio signal outputted from the signal transmitting/receiving circuit 14 to the receiving line 16 are converted to DC level by diode l' 20, 22, and then The signal is added to a comparator 24 for comparing signal levels, and their levels are compared. Depending on the comparison result of comparator 24, switching control circuit 26 generates a mode switching output and applies it to CCA 3.18. When the signal level on the transmitting system 6 side is higher than the signal level on the receiving system 16 side, the CCA 3 is controlled to the signal passing state, and the CCA 18 is controlled to the signal blocking state,
Further, when the signal level on the receiving line 16 side is higher than the signal level on the transmitting line 6 side, the CCA 18 is controlled to pass the signal, and the CCA 3 is controlled to the signal blocking state, thereby controlling the transmitting and receiving lines. Depending on the signal level between 6.16 and 16, the transmitting mode or the receiving mode is set, and voice transmission/reception switching is performed. Then, the signal discrimination circuit 10 discriminates whether the input signal to the transmission system 60 is voice or not.
Only in the case of voice, the switching operation of the switching control circuit 26 is ensured to prevent the transmitting mode from being set only due to noise.

Depending on these mode settings, CCA
The audio signal that has passed through the CCA 18 is sent to the telephone line 12 from the signal transmitting/receiving circuit 14 via the amplifier 28, and in the receiving mode, the audio signal that has passed through the CCA 18 is sent via the amplifier 30 to the speaker 32 of the handset 2. and is played back as the received voice.

[Problem that the invention seeks to solve]

In this way, the switching control circuit 26 uses the signal discrimination circuit 10.
If the switching between transmission and reception is regulated, it is possible to determine whether it is voice or noise when switching between transmission and reception, and prevent malfunctions such as switching to the transmission mode when noise is treated as transmission voice, but when noise and voice are mixed. In this case, since noise is also transmitted as the transmitted voice along with the voice, it is not possible to eliminate the sense of indistinctness due to the noise on the receiving side.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a voice transmission circuit that has a simple configuration, avoids the influence of noise, and improves clarity.

[Means for solving problems]

As shown in FIG. 1, the audio output path of the present invention includes a noise detection means (signal discrimination circuit) that detects whether an input signal applied from a microphone is voice or noise and generates a level output according to the noise level. 10), and level adjustment means (attenuator circuit 34) for adjusting the level of the input signal according to the level output generated by the noise detection means.
).

[For production]

The audio output circuit of the present invention focuses on the fact that a speaker makes a loud noise when there is surrounding noise, and reduces the relative noise level by attenuating the input signal level according to the noise level. , improving the signal-to-noise ratio.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the audio transmission circuit of the present invention.

In FIG. 1, the voice and surrounding noise on the transmitting side enter the microphone 4 of the handset 2, and are added from the microphone 4 to the transmitting line 6 as an input signal on the transmitting side. The input signal applied to the transmission system 6 is amplified by the CCA 3, and then
It is added to the attenuator circuit 34 installed as an input signal level adjustment means, and also added to the signal discrimination circuit 10 installed as a noise detection means.

The signal discrimination circuit 10 discriminates whether the input signal is voice or noise, generates a level output according to the noise level, and applies this level output to the attenuator circuit 34 as a level control input.

The attenuator circuit 34 is a current controlled amplifier (C) whose gain is adjusted by a control input to control the level of the input signal.
The signal discrimination circuit 1 consists of a gain control circuit such as CA).
The amount of attenuation is adjusted by the level output added from 0. Therefore, the output level VMO of the input signal applied from the microphone 4 to the attenuator circuit 34 is adjusted according to the noise level, as shown in FIG.

The level-adjusted input signal from the transmission system 6 side is added to the CCA 3 installed as a signal passing/blocking means, and in the transmission mode, the signal passing through the CCA 3 is passed through the amplifier 28 and sent from the signal transmission/reception circuit 14 to the telephone line. 12, and after being converted to a DC level by a diode 20, it is applied to a comparator 24.

Further, the receiving side audio signal sent from the telephone line 12 is received by the signal transmitting/receiving circuit 14, and is outputted from the signal transmitting/receiving circuit 14 to the receiving system 16 side, and is sent to the receiving system 16 side as a signal passing/blocking means. The signal is applied to the installed CCA 18, and after being converted to a DC level by a diode 22, it is applied to a comparator 24.

The comparator 24 compares the signal levels between the transmitting and receiving channels 6.16, and when the signal level on the transmitting channel 6 side exceeds the signal level on the receiving channel 16 side, it indicates the transmitting mode, e.g. When a low level (L) output is generated and the signal level on the receiving line 16 side exceeds the signal level on the transmitting line 6 side, a high level (L) output is generated indicating the receiving mode.
H) Generate an output. Each output is applied to a switching control circuit 26 installed as a call mode switching means that selects the transmit mode or the receive mode depending on the output. Then, the switching control circuit 26 generates an output for setting the transmitting mode and the receiving mode, and by this output, in the transmitting mode, the CCA 3 on the transmitting system 6 side is in the signal passing state, and the receiving system 1 is in the signal passing state.
The CCA 18 on the 6 side is controlled to be in the signal cut-off state, and in the receiving mode, the CCA 3 is controlled to be in the signal cut-off state, and the CCA 18 is controlled to be in the signal cut-off state.
is controlled to pass the signal.

In this case, the switching control circuit 26 performs transmission/reception switching when the signal on the transmission system 6 side contains voice based on the determination output from the signal discrimination circuit 10 that determines whether the signal on the transmission system 6 is voice or not. and generates a switching control output to prevent malfunctions due to noise.

Then, in the transmitting mode, the audio signal that has passed through the CCA 3 is applied to the signal transmitting/receiving circuit 14 via the amplifier 28, and then
The signal is transmitted from the signal transmitting/receiving circuit 14 to the telephone line 12. Further, in the receiving mode, the audio signal that has passed through the CCA 18 is amplified by the amplifier 30 and then added to the speaker 32 of the handset 2 to be reproduced as receiving audio.

Therefore, since the signal level on the transmission system 6 side is suppressed in accordance with the surrounding noise where the handset 2 is installed, the noise in the transmission signal is reduced. In other words, when the surrounding noise is large, the speaker makes a loud voice in response to the noise, so even if the signal level on the transmission system 6 side is suppressed, the amount of attenuation of the audio component is smaller than the noise. Therefore, the SN ratio can be improved.

Such an operation is equivalent to automatically switching the input sensitivity in response to a change in the installation location of the handset 2 or in response to a change in the level of ambient noise at the installation location. , it is possible to prevent discomfort caused by noise and improve the clarity of voice, allowing for natural conversation.

FIG. 3 shows a specific example of the circuit configuration of the signal discrimination circuit 10 shown in FIG.

As shown in FIG. 3, the signal input section includes an operational amplifier 38.
A logarithmic compression amplifier consisting of a diode 40 and a diode 40 is installed, and the non-inverting input terminal (+) of the operational amplifier 38 receives a signal input from the microphone 4 as well as a bias voltage 8 set at a terminal 42 via a resistor 44. has been added. Therefore, the input signal VINTX applied from the microphone 4 is logarithmically compressed and then sent to the operational amplifier 38.
to the base of transistor 46.

A first time constant circuit 54 consisting of a parallel circuit of a capacitor 50 and a resistor 52 is connected to a terminal 48 provided at the emitter of the transistor 46, and the peak value is detected by this time constant circuit 54 and the transistor 46. The circuit is configured.

The power supply voltage Vcc is applied to the capacitor 50 via the transistor 46, and the emitter of the transistor 46 is charged with the charging voltage (2) of the capacitor 50. Since it is raised by τ1, the output voltage level of operational amplifier 38 applied to the base of transistor 46 becomes the charging voltage of capacitor 50 ■. If it is larger than the conduction reference voltage consisting of τ1 plus the base-emitter distance ■1 necessary for the transistor 46 to conduct, the transistor 46 conducts and the capacitor 50 is charged, but the operational amplifier 38 If the output voltage level is less than its conduction reference voltage,
Transistor 46 becomes non-conductive, and capacitor 50 is discharged using resistor 52 as a discharge loop in accordance with the signal voltage level. As a result, the capacitor 50 holds the ever-changing peak value of the input signal. In this case, when the capacitance of the capacitor 50 is Cp and the resistance value of the resistor 52 is R3, the time constant τ1 of the time constant circuit 54 is τ
1 = R1·C1, charging and discharging of the capacitor 50 is regulated by this time constant τ1. Therefore,
Since the level change of audio is larger than that of continuous noise, in the case of audio, the charging voltage of the capacitor 50 is ■. Whereas τ1 changes significantly, in the case of noise, it is a stable level that is determined according to the level of the continuous noise.

The charging voltage V0τ1 of this capacitor 50 is applied to the non-inverting input terminal (+) of the first comparator 56, and is applied to the terminal 58
The charging voltage of the capacitor 62 of the second time constant circuit 64 consisting of a series circuit of a resistor 60 and a capacitor 62 connected to It is compared with τ2. The resistance value of the resistor 60 is R2,
If the capacitance of the capacitor 62 is 02, then the time constant circuit 64
The time constant τ2 of is given by τ2=R2・C2, but its value is greater than the time constant τ of the time constant circuit 540 (τ
2>τ, ).

The time constants τ1 and τ2 are set in such a relationship because the voice to be detected is discontinuous and the noise is continuous, so the time constants τ1 and τ2 are set in consideration of the interval at which the voice level changes. This is to distinguish it from noise. That is, the time constant τ2 is set so that the capacitor 62 is discharged when the noise arrives and charged when the voice arrives, and when the voice continues to hold the capacitance C2 of the capacitor 62, the charging voltage . τ2 is set to be higher than the charging voltage voτ of the capacitor 50.

Then, the comparator 56 changes the bias condition of the diode 66 installed on the output side according to the comparison output,
Depending on whether the diode 66 is conductive or not, the capacitor 6
Switch between charging and discharging in step 2.

Therefore, the charging voltage of the capacitor 50 is applied to the non-inverting input terminal (+) of the comparator 56. τ1 is the charging voltage of the capacitor 62. When τ2 or more, the comparison output of the comparator 56 becomes a high level (H) output, and the diode 66
becomes a reverse bias state. This represents the arrival of audio, and capacitor 62 is charged until diode 66 is forward biased, eventually reaching the charging voltage of capacitor 50 ■. ■High charging voltage exceeding τ1. Charged to τ2.

Also, the charging voltage of the capacitor 50 is applied to the non-inverting input terminal (+) of the comparator 56. τ1 is the capacitor 62
■ Charging voltage. When it becomes less than 12, the comparison output of the comparator 56 becomes a low level (L) output, and the diode 66 becomes forward biased. This represents the arrival of noise, and the capacitor 62 is discharged, and its discharge reduces its charging voltage ■. This continues until diode 66 becomes reverse biased due to τ2.

By the way, even when the voice arrives, the charging voltage of the capacitor 50 is instantaneous. τ1 is the charging voltage V of the capacitor 62. τ2
It is expected that the time will be below, but the time constant is 2
In the following case, since the capacitor 62 is not discharged, the charging voltage V of the capacitor 62 is equal to the case where the sound is isometrically continuing. τ2 maintains a certain level representing the voice with little or no change.

And the charging voltage of each capacitor 50.62 ■oτ1,
Voτ2 is applied to a second comparator 68 and compared. In this case, the comparator 68 has a non-inverting input terminal (+)
. Since Voτ2 is added to the inverting input terminal (-) of τ, the comparator 6th outputs H when ■oτ>yoτ2 (during audio), and outputs H when ■oτ2>■oτ1 (during noise). It becomes L output. Each output is applied to the switching control circuit 26 as a control input to prevent the inconvenience of setting the transmit mode only due to noise.

Further, the charging voltage V of the capacitor 50 is output from the emitter side of the transistor 46 . τ1 is an input signal V applied to the inverting input terminal (-) of the DC amplifier 70, logarithmically compressed by a logarithmic compression amplifier consisting of an operational amplifier 72 and a diode 74, and applied to the non-inverting input terminal (+).
It is compared and amplified with 1hlTX. The DC amplifier 70 has a logarithmically compressed output level of the input signal equal to the charging voltage of the capacitor 50 . Generates a voltage output proportional to the level exceeding τ1. This voltage output is connected to transistor 76 and resistor 78.
It is converted into a current by a voltage/current conversion circuit B80 consisting of: This current flows as a control current to the attenuator circuit 34, and an attenuation gain is set in the attenuator circuit 34 according to the current.

Therefore, the input signal applied to the attenuator circuit 34 passes through the attenuator circuit 34 whose attenuation amount is set according to the noise level, and is converted into a signal at a level corresponding to the noise level and sent out. When the surrounding noise is large, the discomfort caused by the noise of the transmitted voice can be suppressed, and a natural conversation can be carried out.

Although the embodiment has been described using a telephone device as an example, the present invention can be used not only for such a telephone device but also for switching various signal systems.

〔Effect of the invention〕

As explained above, according to the present invention, by suppressing the input signal level from the microphone according to the noise level, the ratio of the audio component to the noise component is increased with a simple configuration, and the noise caused by the noise in the transmitted audio is increased. I can feel (■) pleasure.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a telephone device which is an embodiment of the voice transmission circuit of the present invention, FIG. 2 is a diagram showing the characteristics of the attenuator circuit in the telephone device shown in FIG. 1, and FIG. FIG. 4 is a circuit diagram showing a specific circuit configuration example of a signal discrimination circuit in the telephone device shown in FIG. 4, and FIG. 4 is a block diagram showing a conventional telephone device. 10... Signal discrimination circuit as noise detection means, 34
...Attenuator circuit as a level adjustment means.

Claims (1)

[Claims] noise detection means for determining whether an input signal applied from a microphone is voice or noise and generating a level output according to the noise level; An audio output circuit characterized by comprising: a level adjustment means for adjusting the level adjustment means for adjusting the level adjustment means for adjusting the level adjustment means for adjusting the level adjustment means for adjusting the level adjustment means;