JPS62130048A - Sound switch circuit - Google Patents

Abstract

PURPOSE:To prevent malfunction due to noise and to attain the changeover between signal systems with high reliability by changing a level comparison condition of a comparison means depending on a noise level. CONSTITUTION:A noise discriminating circuit 20 discriminates whether sound or a noise depending on the waveform of the sound or noise and outputs a level output VN in response to the noise level as a noise discrimination output when it is judged as noise. The output is fed to a comparator 18 as an input offset control input and the input offset of the comparator 18 is changed continuously by the noise discrimination output so as to switch the input sensitivity at the transmission and reception side relatively. The level is compared via the comparison condition as above and when a sound signal level of a transmission system 6 exceeds that of a reception system 16, the comparator 18 generates an L level of the transmission mode and when less than that, an H level of the reception mode is generated, and the result is outputted to a changeover control circuit 22. The circuit 22 sets the mode depending on the output and applies signal passing/signal disconnection signal disconnection/signal passing to current control amplifiers 24, 26 respectively.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention selects a signal system through which a signal should be passed by comparing audio signal levels between various signal systems, such as between transmitting and receiving signal systems of a telephone device. The present invention relates to an audio switch circuit for switching, and in particular to preventing switching malfunctions due to noise.

[Conventional technology]

Traditionally, speakerphones and interfaces have been installed on a tabletop with a handset consisting of a microphone and a speaker, allowing the caller to send and receive calls without having to pick up the handset. Telephone devices such as phons have been proposed.

This kind of telephone equipment compares the levels of the voice signal input from the microphone and the voice signal sent from the telephone line, and conducts the signal system on the higher level side, and connects the signal system on the lower level side. A cut-off audio switch circuit is installed, and this audio switch circuit switches between signal systems according to the audio level, thereby realizing transmission/reception switching.

[Problem that the invention seeks to solve]

When switching between signal systems is performed using such an audio switch circuit, continuous noise emitted by a machine, a car, etc. may be added to the microphone depending on where the handset is installed.

The noise level added to the microphone is the voice of the receiver 13
If the signal level is exceeded, the device will always be in transmit mode, and the other party's voice cannot be played back, which may interrupt the call.

SUMMARY OF THE INVENTION An object of the present invention is to provide an audio switch circuit that prevents malfunctions caused by noise and realizes highly reliable switching between signal systems.

[Failure to solve the problem]

As shown in FIG. 1, the audio switch circuit of the present invention has the following features:
Comparison means for comparing the levels of audio signals in the audio switch circuit IO that compares audio signal levels between signal systems (sending side signal system 6, receiving side signal system 16) and selects a signal system through which the signal should pass. The level comparison conditions of (comparison RHI8) are changed according to the noise level.

[For production]

The audio switch circuit of the present invention prevents switching malfunctions due to comparison errors caused by noise by changing the level comparison conditions of the comparison means according to the noise level.

In the audio switch circuit of the present invention, the level comparison condition of the comparison means can be changed according to the noise level, for example.
This is achieved by changing the input off value of the comparing means according to the noise level to make the sensitivity to the voice signal on the transmitting side dull.

〔Example〕

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

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

In FIG. 1, the voice on the transmitting side and surrounding noise enter the microphone 4 of the handset 2, and are added to the transmitting side signal system 6 (hereinafter simply referred to as the transmitting system 6) as a transmitting side audio signal by the microphone 4. It will be done. The voice signal applied to the transmission line 6 is amplified by an amplifier 8 and then sent to a voice switch circuit 10 as a call switching means.

Also, the receiving side audio signal sent from the telephone line 12 is sent to a signal transmitting/receiving circuit 14 called Speechnet Nok.
The receiving signal VA received by the signal transmitting/receiving circuit 14
N□ is output to the receiving side signal system 16 (hereinafter simply referred to as the receiving system 16) and is applied to the audio switch circuit 10.

The audio switch circuit 10 includes a comparator 18 whose input offset can be changed as means for comparing signal levels in order to compare audio signal levels between each system 6.16, and a comparator 18 that can change the input offset and determines whether the signal of the transmission system 6 is noise or voice. Noise discrimination circuit 2 that discriminates and generates an output according to the determined noise level.
0 is set.

The noise discrimination circuit 20 normally discriminates between noise and speech based on the form of the waveforms, since speech has discontinuous waveforms depending on the state of pronunciation, and noises to be avoided occur one after another. If it is determined that this is the case, as shown in FIG. 2, a level output (8) corresponding to the noise level is output as a noise discrimination output. This output is the comparator 18
The input offset of the comparator 18 is Nj by the noise discrimination output.
It is continuously changed, and the input sensitivities of the transmitting side and the receiving side are relatively switched.

The change in human power sensitivity due to this noise is, for example, as shown in 8 in FIG.
If the transmission signal VINTX containing the noise N
Since it generates an output ■9 with a level corresponding to
As shown in FIG.
is changed and the human power offset VINor is high in the section t+
, tz, the input sensitivity of the receiving system 1 with respect to the input sensitivity of the transmitting system 6 side.
The sensitivity to human power on the 6th side increases. In addition, in B of FIG. 3, 1o represents the discrimination time of the noise discrimination circuit 20.

Therefore, in the comparator 18, the comparison condition is relatively changed according to the noise level of the place where the handset 2 is installed, and the level of the audio signal of the six examples of the transmitting system is different from the noise level. If it is not exceeded, the audio signal on the receiving system 16 side will not be compared.

After passing through these comparison conditions, a level comparison is performed by the comparator [8], and the audio signal level of the six transmitting channels is compared to the receiving channel 16.
When the audio signal level of the receiving system 16 exceeds the audio signal level of the transmitting system 6, the comparator 18 generates a low level (■7) output indicating the transmitting mode, and the audio signal level of the receiving system 16 If the audio signal level exceeds the level of the audio signal, the comparator 18
generates, for example, a high level (tI) output to indicate the listen mode. Each output is applied to a switching control circuit 22 installed as a call mode switching means that selects a send mode or a receive mode depending on the output.

Then, the switching control circuit 22 generates an output for setting the transmitting mode and the receiving mode, and by this output, in the transmitting mode, the current control amplifier (OCA) installed on the transmitting system 6 side as a signal passing/cutting means ) 24 is in the signal passing state,
A current control amplifier (OCA) 2.6 installed as a signal passing/blocking means on the receiving system 16 side is controlled to a signal blocking state, and in the receiving mode, the CCA 24 is controlled to a signal blocking state and the CCA 26 is controlled to a signal passing state. be done.

Therefore, in the transmitting mode, the audio signal that has passed through the CCA 24 is applied to the signal transmitting/receiving circuit 14 via the amplifier 28, and then is sent from the signal transmitting/receiving circuit 14 to the telephone line 12. In addition, in the receiving mode, the audio signal that has passed through the CCA26 is
After being amplified by the amplifier 30, it is added to the speaker 32 of the handset 2 and reproduced as received voice.

As explained above, the comparison conditions of the comparator 18 are changed according to the surrounding noise of the place where the handset 2 is installed, and the manual sensitivity of the voice switch circuit 10 is continuously switched, so that the caller can While intuitively grasping the switching state, it is possible to make a call by increasing the volume of the generated sound in accordance with the input sensitivity set according to the noise level.

In addition, this audio switching Sochi circuit 10 can automatically switch the human power sensitivity according to changes in the installation location of the handset 2 and according to changes in the level of ambient noise at the installed location. According to the switch circuit 10, malfunctions in call switching due to noise are prevented, and stable call switching can always be realized.

FIG. 4 shows a specific circuit configuration example of the comparator 18 and the noise discrimination circuit 20 of the audio switch circuit 10 shown in FIG.

In the noise discrimination circuit 20, the operational amplifier 34 and the diode 36 constitute a logarithmic compression amplifier, so the audio signal VINTX applied from the transmission system 6 to the non-inverting input terminal (+) of the operational amplifier 34 is logarithmically compressed. is then applied to the base of transistor 38. transistor 3
A terminal 40 provided at the emitter of the capacitor 4
a first time constant circuit 46 consisting of a parallel circuit of 2 and a resistor 44;
The time constant circuit 46 and the transistor 38 constitute a peak value detection circuit. That is, the power supply voltage VCC is applied to the capacitor 42 via the transistor 38, and the emitter of the transistor 38 is charged with the charging voltage (2) of the capacitor 42. It is lifted by τ1. Therefore, the output of the operational amplifier 34 is the charging voltage V of the capacitor 42. If τ1 is larger than the base-emitter voltage 1 required for the transistor 38 to conduct, the L transistor 38 becomes conductive and the capacitor 42 is charged by the signal, but the operational amplifier 34 The output is the charging voltage of the capacitor 42 ■. If the voltage is smaller than the sum of τ1 and the base-emitter VRE necessary for the transistor 38 to conduct, the charging voltage v0τ1 of the capacitor 42 is discharged using the 1° resistor 44 as a discharge loop according to the signal level. Therefore, as shown in FIG. 5, the capacitor 42 holds the ever-changing peak value of the audio signal. In this case, if the resistance value of the resistor 44 is R1 and the capacitance of the capacitor 42 is C7, the time constant τ1 of the time constant circuit 46 is
Since it is given by τ1-R1·CI, charging and discharging of the capacitor 42 is regulated by this time constant τ. Therefore,
Since audio has a large level change compared to continuous noise, the charging voltage of the capacitor 42 is ■. τ1 causes a large change, whereas in the case of noise, it becomes a stable level that is determined according to the level of noise depending on its continuity.

Charging voltage V of capacitor 42. τ, is the first comparator 4
The charging voltage ■ of the capacitor 54 of the second time constant circuit 56 consisting of a series circuit of a resistor 52 and a capacitor 54 connected to the terminal 50 is applied to the non-inverting input terminal (+) of 8. It is compared with τ2.

1 degree resistance value of 1 degree tj”c 52 is R2, capacitor 54
If each term is C2, the time constant τ2 of the n,'1 constant circuit 56 is given by τ2-R2・C2, but its value is determined by the discontinuity of the voice, the continuity of the noise, and the magnitude of the level. In order to determine whether the signal is noise or noise, the time constant of the time constant circuit 4G is set to a value larger than the time constant τ1 (τ2>τ1).

The comparator 48 changes the bias condition of the diode 5B installed on its output side according to the comparison output, and switches the charging and discharging of the capacitor 54 by turning the diode 58 on and off. That is, the charging voltage of the capacitor 42 is applied to the non-inverting input terminal (+) of the comparator 48. τ
, becomes equal to or higher than the charging voltage of the capacitor 54 ■oτ2, the comparison output of the comparator 48 becomes a high level (IX) output, and the diode 58 becomes reverse biased. This represents the arrival of the voice, and the capacitor 54 is charged as shown in FIG. 6 to its charging voltage ■. τ2 charges diode 58 until it becomes forward biased. In Figure 6, t is a charged state! If false, R2 represents a state in which charging has ended and the charged state is maintained.

Also, the charging voltage (■) of the capacitor 42 is applied to the non-inverting input terminal (→-) of the comparator 4B. τ,=1=charging voltage V of the capacitor 54. 12, the comparison output of the comparator 48 becomes a low level (L) output, and the diode 58
becomes a forward bias state. This represents the arrival of noise, and the -1-yapacitor 54 has its charging voltage ■. τ2
By this, the diode 58 is increased by 13 times until the diode 58 becomes a reverse high voltage.

By the way, even when a voice arrives, the charging voltage V of the capacitor 42 is instantaneous. τ1 is the charging voltage of the capacitor 54■. τ2
It is expected that the time will be less than the time constant τ2
In the following cases, the capacitor 54 is not discharged, so if the sound continues equivalently, the charging voltage of the capacitor 54 is 2, as shown at 2 in FIG. τ2 remains at a certain level with little or no change and does not represent sound.

Charging voltage V of each capacitor 42.54. r,, Voτ2
are added to the second comparator 60 and compared. In this case, the comparator 60 has a non-inverting input terminal (+). r2,
V to the inverting input terminal (-). Since τ1 is added,
Voτ, l-1 output when >yoτ2 (voice), V
7 outputs when oτ2 > VOr 1 (at the time of noise). The switch circuit 62 is switched by the comparison output of the comparator 60, and becomes non-conductive at its I-1 output and conductive at its L output.

Therefore, the buffer circuit 64 is activated only when there is a noise that causes the switch circuit 62 to conduct.
DC output according to the noise level at the time of noise from 4 to tti for changing the comparison condition for the comparator 18.
Added as a control signal.

In this embodiment, the output (1)8 is applied to the comparator 18 as a control power to change the power offset of the comparator 18.

The ratio 1kRa18 is 11 to a difference amplifier consisting of a transistor 66.68 and a constant current 1
For a differential comparator to which a current mirror circuit consisting of a transistor 72.74 as a differential load is added, and an output circuit consisting of a Langistaffe 6.78, a constant current source 80, and a resistor 82 is added. In addition, an offset circuit 84 is added.

The offset circuit 84 is constructed by adding a transistor 90 and a resistor 92 as switching means for switching the current flowing through the transistor 86 to the current mirror circuit composed of transistors 86 and 88.

Therefore, at the time of noise, the current flowing through the transistor 90 is controlled by the output 9 whose level changes according to the noise level output from the buffer circuit 64. 111 will be sent. Electric power 1 [changed according to this noise level] is
Through the current mirror circuit of transistors 86 and 88, the current flows to the 1-transistoro 6 side, and the current flows to the transistor 66.
．． Input offset (2) corresponding to the current flowing into the differential amplifier consisting of the constant current source 68 and the constant current source 70. , is set. Note that during audio, the switch circuit 62 becomes non-conductive and the buffer circuit 64 does not operate, so the operation of the transistor 90 is stopped and the operation of the offset circuit 84 is in a stopped state.

The manual offset V1.4°, set by the offset circuit 84, is the output VN of the hasher circuit 64.
Since the noise level is changed according to the noise level, the voice power sensitivity of the transmitting system 6 side decreases, and the voice signal level of the receiving system 16 side is changed only when the audio signal level from the transmitting system 6 side is sufficiently higher than the noise level. compared with the audio signal. As a result of the comparison, if the audio signal level on the transmitting system 6 side exceeds the audio signal level on the receiving system 16 side, the transistor 66 becomes conductive and the transistor 68 becomes non-conductive, so that the transistor 76 becomes non-conductive. , the comparison output taken out from the emitter side of the transistor 78 becomes L level, and the transmitting mode is set. Further, when the audio signal level of the receiving system 16 exceeds the audio signal level of the transmitting system 6, the transistor 68 becomes conductive and the transistor 66 becomes non-conductive, so the transistor 76 becomes conductive and the transistor 78 becomes conductive. The comparison signal taken out from the emitter side is at level 1, and the reception mode is set.

Therefore, if such a ratio 'F' QR 318 and the noise discrimination circuit 20 are used, the conditions for comparing the audio signal level between each system 6.16 can be changed according to the noise level,
Zhou: Malfunctions in call switching due to sword noise can be prevented, and natural call switching can be realized.

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 changing the level comparison conditions of the comparison means according to the noise level, switching malfunctions due to comparison errors caused by noise can be prevented, and highly reliable signal switching can be achieved. realizable.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a telephone device which is an embodiment of the voice switch circuit of the present invention, FIG. 2 is a diagram showing the operation of the noise discrimination circuit of the voice switch circuit in the telephone device shown in FIG. 1, and FIG. The figure is a diagram showing the operation of the voice switch circuit in the telephone device shown in FIG. 1, and FIG. 4 is a specific circuit configuration example of the comparator and noise discrimination circuit of the voice switch circuit in the telephone device shown in FIG. Circuit diagram showing 5th
This figure shows the output waveform of the first time constant circuit section of the noise discrimination circuit, and FIG. 6 shows the output waveform of the second time constant circuit section. 6... Sending side signal system, 10... Audio switch circuit, 16... Receiving side signal system, 18... Comparator, 20
...Noise discrimination circuit. Noise level Figure 2 Figure 3

Claims (1)

[Claims] In an audio switch circuit that compares audio signal levels between signal systems and selects a signal system through which the signal should pass,
An audio switch circuit characterized in that a level comparison condition of a comparing means for comparing the levels of audio signals is changed according to a noise level.