JPH0738635A - Side tone level control circuit for telephone set - Google Patents

Abstract

PURPOSE:To vary a side tone level in response to the quantity of a bypassed signal between a transmitter and a receiver at a line side by adding a side tone and a received voice signal, amplifying the sum with an amplifying section, selecting one of plural addition ratios and attenuating the amplified transmission voice signal with a variable attenuation section. CONSTITUTION:A transmission voice A outputted from an AMP 15 is attenuated by a variable attenuation section 3, added to a received voice signal B and amplified at an AMP 23 and the amplified sum signal is outputted to a receiver (SP) 21. The sum ratio is varied with the ratio of the resistance of resistors R24, R31 and the ratio of the resistance of resistors R24, R32 through the changeover of a SW 34. A side tone ratio outputted from the SP 21 is changed by the change in the sum ratio. The SW 34 is used to select the R31 in the analog line system and the SW 34 is used to select the R32 in the digital line system. Since the sum ratio of the AMP 23 is larger with a smaller input resistance, the resistance of the R31 is larger than the resistance of the R32. Thus, when a system select signal being a control signal is a signal selecting the digital line system, the SW34 throws the output from the AMP 15 to the position of the R32 to increase the side tone level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a side tone level control circuit for a telephone, and more particularly to a side tone level control circuit for a telephone in a car telephone system.

[0002]

2. Description of the Related Art A side tone level control circuit for a conventional telephone will be described with reference to the drawings.

FIG. 2 is a circuit diagram showing an example of a side tone level control circuit of a conventional telephone.

In FIG. 2, this conventional example shows a resistor (R).
A microphone (MI that is supplied with a bias voltage via 42).
The output signal of (C) 41 is blocked by the capacitor (C) 43 from the direct current, and passes through R 44 to the operation amplifier (A
It is amplified by MP) 45 and is output as a transmission voice A.
At this time, the amplification degree of the AMP 45 is adjusted by the ratio of R44 and R46.

The received voice B received is amplified by the AMP 53 through R52 and is amplified by the receiver (SP) 51. At this time, the amplification degree of the AMP53 is adjusted by the ratio of R54 and R52, but the transmission voice A is R55 in the AMP53.
Since it is input as a sidetone through, the magnitude of the sidetone is also adjusted by the ratio of R54 and R55.

That is, if R52 and R54 are determined, the amplification level of the received voice is also determined, and if R52 and R55 are determined, the sidetone level is also uniquely determined.

[0007]

The side tone level control circuit of this conventional telephone has R54 and R55 as shown in FIG.
Since the side tone level is uniquely determined by,
For example, there is a problem that the sidetone level cannot be suppressed to a low level when there is a large amount of signal wraparound between transmission and reception on the line side.

On the other hand, if R54 and R55 are determined so that the sidetone level becomes good when the signal wraparound between the transmission and the reception on the line side is large, the line with little signal wraparound can be obtained. However, there is a problem in that the sidetone level is low and it becomes difficult to hear.

[0009]

A side tone level control circuit of a telephone according to the present invention attenuates a received voice and the amplified transmitted voice with an amplification section for amplifying a transmitted voice from a transmitter. An addition amplification unit that amplifies the added voice with the sidetone and outputs the added voice to the receiver, and a plurality of predetermined addition ratios of the sum of the received voice and the sidetone with respect to the sidetone by an external control signal. A variable attenuator for attenuating the transmitted voice that is selected and amplified.

Further, in the side tone level control circuit of the telephone of the present invention, the amplifying section has a first resistor for supplying a bias voltage to the transmitter and one end of the resistor connected to the transmitter. A capacitor for blocking direct current due to voltage, a second resistor having one end connected to this capacitor, and a first operation for amplifying the transmitted voice by connecting one end of the input to the other end of the second resistor. An amplifier and a third resistor that adjusts the amplification degree of the first operation amplifier according to the ratio of the second resistor, and the summing amplification unit has a fourth resistor that receives the received voice at one end. , A second operational amplifier that connects one end of the input to the other end of the fourth resistor and amplifies the received voice and outputs the amplified voice to the receiver, and the second operational amplifier according to the ratio of the fourth resistor. Amplification of And a fifth resistor to adjust,
The variable attenuator includes sixth and seventh resistors whose one ends are both connected to one end of the input of the second operational amplifier,
A switch for selectively connecting the output of the first operational amplifier to the other end of the sixth or seventh resistor according to the control signal.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In FIG. 1, this embodiment is based on a transmitter (MI
C) Amplifying unit 1 for amplifying the transmitted voice from 11 and addition amplifying unit 2 for amplifying the added voice of the received voice B and the side sound with the attenuated transmitted voice A and outputting the amplified voice to the handset (SP) 21. And a variable attenuator 3 for attenuating the transmitted voice A by selecting one of a plurality of predetermined addition ratios of the sum of the received voice B and the sidetone with respect to the sidetone by a control signal C from the outside. Have
The amplification unit 1 includes a resistor (R) 12 for supplying a bias voltage to the MIC 11, a capacitor (C) 13 connected to the MIC 11 for blocking a direct current due to the bias voltage, an R 14 having one end connected to C 13, and an input. The addition amplification unit 2 includes an operation amplifier (AMP) 15 having one end connected to the other end of R14 for amplifying the transmitted voice and R16 for adjusting the amplification degree of the AMP15 according to the ratio of R14. R22 which receives B and one end of the input is R22
The variable attenuator 3 includes an AMP23 connected to the other end of the AMP23 for amplifying the received voice B and outputting it to the SP21, and an R24 for adjusting the amplification degree of the AMP23 according to the ratio of R22. R31 and R3 connected to
2 and a switch (SW) 3 for selectively connecting the output of the AMP 15 to the other end of R31 or R32 by the control signal C
4. AM including the side tone that attenuates the output of the AMP 15 via R31 or R32 and the received voice B via R22.
It is configured to be added to P23.

Next, the operation of this embodiment will be described.

Since the operation of the amplifying section 1 of this embodiment is the same as that of the conventional example, it will be omitted.

The transmitted voice A output from the AMP 15 is
It is attenuated by the variable attenuator 3, added and amplified with the reception voice B by the AMP 23, and output to the SP 21. In this embodiment, the control signal C is a system select signal for selecting an analog line system or a digital line system.

In general, in a digital line system, the sneak of signals between transmission and reception on the line side is reduced by adopting the echo canceller technology. In the analog line system, the signal wraparound between the transmission and reception is larger than that in the digital line.

In the present embodiment, the addition ratio is such that the ratio of the resistance values of R24 and R31 or the ratio of the resistance values of R24 and R32 can be changed by switching SW34. The sidetone level output from is changed.

In this embodiment, the R31 side is selected by the SW34 in the analog line system and the R32 side is selected by the SW34 in the digital line system. The addition ratio of the AMP23 becomes larger when the input resistance is smaller. Therefore, the resistance value of R31> the resistance value of R32.

Therefore, for example, when the system select signal of the control signal C is a signal for selecting the system of the digital line, the SW 34 connects the output from the AMP 15 to the R32 side to increase the side tone level.

[0021]

As described above, the present invention amplifies the added voice of the amplifier for amplifying the voice transmitted from the transmitter, and the side voice obtained by attenuating the voice received and the amplified voice transmitted. And output to the receiver, and one of a plurality of predetermined addition ratios of the sum of the received voice and the sidetone with respect to the sidetone is selected by the control signal from the outside and amplified transmission is performed. By having the variable attenuator for attenuating the voice, the sidetone level can be switched and used at an appropriate sidetone level even in a line in which the signal wraparound between the reception and transmission is large or small.

Further, when the control signal is, for example, a system select signal, an independent side tone level is set for each line instead of switching between the analog line system and the digital line system, so that the user can switch the line. Can be made unconscious.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 amplification part 2 addition amplification part 3 variable attenuation part 11 transmitter (MIC) 12,14,16,22,24,31,32 resistance (R) 13 capacitor (C) 15,23 operation amplifier (AMP) 21 receiver (SP) 34 Switcher (SW) A Transmitted voice B Received voice C Control signal

Claims (2)

[Claims] 1. An addition unit for amplifying a voice transmitted from a transmitter, and an addition amplifier for amplifying a voice added to a voice received and a side tone obtained by attenuating the amplified voice and outputting the amplified voice to a receiver. Section, and attenuating the amplified transmission voice by selecting one of a plurality of predetermined addition ratios of the sum of the reception voice and the sidetone with respect to the sidetone by a control signal from the outside. A sidetone level control circuit for a telephone, comprising a variable attenuator. 2. The amplification unit includes a first resistor for supplying a bias voltage to the transmitter, a capacitor having one end connected to the transmitter and blocking a direct current due to the bias voltage, and one end Depending on the ratio between the second resistor connected to this capacitor, the first operational amplifier for amplifying the transmitted voice by connecting one end of the input to the other end of the second resistor, and the second resistor. A third resistor for adjusting the amplification degree of the first operational amplifier, wherein the summing amplification unit has a fourth resistor for receiving the received voice at one end and another resistor for inputting one end of the input to the fourth resistor. A fifth operation amplifier, which is connected to an end and amplifies the received voice and outputs the amplified voice to the receiver, and the amplification degree of the second operation amplifier is adjusted by a ratio of the fourth resistor to the fifth operation amplifier.
And a sixth and a seventh resistor whose one end is connected to one end of the input of the second operational amplifier together.
A switch for selectively connecting the output of the first operational amplifier to the other end of the sixth or seventh resistor according to the control signal, the first or second resistor via the sixth or seventh resistor. 2. The sidetone level control of the telephone according to claim 1, wherein the sidetone in which the output of the operational amplifier of FIG. 2 is attenuated and the received voice through the fourth resistor are added to the second operational amplifier. circuit.