JPH03208452A - Transmission reception amplifier circuit for telephone set - Google Patents

Abstract

PURPOSE:To keep an amplification factor of a reception amplifier circuit to a prescribed value even when a line resistance from a telephone circuit network till a telephone station is large by applying a constant current and a constant voltage to a transmission amplifier section and a reception amplifier section. CONSTITUTION:A DC current from a telephone station 6 is sent to a rectifier circuit 13 via a transmission terminal 42 via a telephone circuit network 41, the polarity of the DC current is made coincident and fed to a constant current/ constant voltage circuit 14. The constant current/constant voltage circuit 14 applies a prescribed voltage to a transmission amplifier circuit 11 and a reception amplifier circuit 12. Thus, even when a line resistance from a telephone circuit network 41 till a telephone station 6 is large, the amplification factor of the reception amplifier circuit 12 is kept to a prescribed value.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a telephone transmission/reception amplifier circuit.

[Prior Art] FIG. 3 is a diagram showing an example of the circuit configuration of a headset used in a conventional telephone reception desk.

In this conventional example, a transmitter/receiver circuit 1 is connected to a transmitter 2 and a receiver 3, and the transmitter/receiver circuit 1 is connected to a telephone station 6 via a reception desk 4 and a telephone line 5. Further, the transmitting/receiving circuit l includes a transmitting amplifying circuit 11, a receiving amplifying circuit 12, and a rectifying circuit 13, and the reception desk 4 has a telephone circuit network 41. The input side of the transmitting speech amplifier circuit 11 is connected to the transmitter 2, the output side thereof is connected to the transmitting terminal 42 of the telephone circuit network 41,
The handset 3 is connected to a telephone network 41 via a receiver amplifier 12.
It is connected to the receiving terminal 43 of. Further, power for the transmitting amplifier circuit 11 and the receiving amplifier circuit 12 is supplied from a rectifier circuit 13 .

In this conventional circuit, the telephone station 6
When power is supplied from the transmitter amplifier circuit 11, the transmitter amplifier circuit 11 operates.
The voice of the caller is amplified and sent to the telephone office 6 through the telephone circuit network 41. On the other hand, the receiving signal from the telephone station 6 is
The signal is amplified by the receiver amplifier circuit 12 via the receiver terminal 43 and transmitted to the receiver via the receiver 3.

[Problems to be Solved by the Invention] In the conventional device described above, when the call signal from the subscriber (high-loss subscriber) is small, the receive signal from the receive terminal 43 is amplified by the receive amplifier circuit 12. can do.

However, the output voltage of the rectifier circuit 13 varies depending on the line resistance from the telephone network 41 to the telephone office 6, and accordingly, the amplification factors of the transmitting amplifier circuit 11 and the receiving amplifier circuit 12, the maximum level There is a problem in that the current level fluctuates, making it impossible to ensure appropriate reception and transmission levels.

Further, in the above conventional example, by operating the reception desk 4, the transmitting circuit of the telephone line network 41 can be controlled when on hold (when the transmission of the transmitting signal is stopped while the telephone line 5 is captured). When the transmission is stopped by cutting or shorting the telephone station 6, the power supply to the reception amplifier circuit 12 is also stopped, so there is a problem that the reception signal from the telephone office 6 cannot be monitored.

SUMMARY OF THE INVENTION An object of the present invention is to provide a telephone transmitting/receiving amplifier circuit that can maintain the amplification factor of the receiving amplifier circuit at a predetermined value even if the line resistance from the telephone circuit network to the telephone office is large.

Another object of the present invention is to provide a telephone transmitting/receiving amplifying circuit that is capable of monitoring incoming calls even when the telephone is on hold.

[Means for Solving the Problems] The present invention is a constant current/constant voltage circuit that is supplied with power from a rectifier circuit, and is a constant current/constant voltage circuit that supplies a constant current and a constant voltage to a transmitting amplifying section and a receiving amplifying section. It has a circuit.

Further, the present invention provides a power storage unit that is charged with power from the rectifier circuit, and when the output voltage of the power storage unit is higher than the output voltage of the rectifier circuit, the reception signal from the telephone network is transmitted to the reception amplification unit. This is to switch the transmission so that it is sent to the handset without going through it.

[Function] The present invention supplies a constant current and a constant voltage to the transmitting amplifier and the receiving amplifier, so even if the line resistance from the telephone network to the telephone office is large, the amplification factor of the receiving amplifier circuit can be maintained at a predetermined level. value can be maintained.

Further, the present invention provides a power storage unit that is charged with power from the rectifier circuit, and when the output voltage of the power storage unit is higher than the output voltage of the rectifier circuit, the reception signal from the telephone network is transmitted to the reception amplification unit. Since the call is sent to the handset without going through the phone, it is possible to monitor the call even when the call is on hold.

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

In this embodiment, a transmitting/receiving circuit 1 is connected to a transmitter 2 and a receiver 3, and the transmitting/receiving circuit 1 is connected to a telephone station 6 via a reception console 4 and a telephone line 5.

The transmitting/receiving circuit l includes a transmitting amplifying circuit 11 that amplifies the transmitting signal.
, a receiver amplifier circuit 12 that amplifies the receiver signal, a rectifier circuit 13 that matches the polarity of the current supplied from the telephone line 5 with the polarity of the load, and a constant current/constant voltage circuit supplied from the rectifier circuit 13. It includes a constant current/constant voltage circuit 14 that supplies constant current and constant voltage to the transmitting amplifying section 11 and the receiving amplifying section 12.

The transmitting/receiving circuit 1 also includes a power storage unit 16 that is charged with power from the rectifier circuit 13 and a voltage comparison unit 1 that detects that the output voltage of the power storage unit 6 is higher than the output voltage of the rectifier circuit 13.
7, when the output voltage of the power storage unit 16 is higher than the output voltage of the rectifier circuit 13, the reception signal from the telephone circuit network 41 is
It has a receiver circuit switching section 15 that switches the signal to be sent to the receiver without going through the receiver amplifier section 12, and a booster circuit 18 that raises the voltage to a voltage sufficient for the receiver circuit switching section 15 to operate.

The receiving circuit switching unit 15 has a fixed terminal 151 connected to the output terminal of the receiving amplifier circuit 12, a fixed terminal 152 connected to the receiving terminal 43 without going through the receiving amplifier circuit 12,
It has a switching terminal 153 connected to the receiver 3. Then, under the control of the voltage comparator 17, the receiving circuit switching unit 15 determines that when the output voltage of the rectifier circuit 13 and the output voltage of the power storage unit 16 are the same, the switching terminal 1''53 is set to the fixed terminal 1.
51 to supply the output signal of the receiver amplifier circuit 12 to the receiver 3, and to supply the output signal of the receiver amplifier circuit 12 to the receiver 3.
When the output voltage of
52 and supplies the signal from the receiver terminal 43 to the receiver 3.

The reception desk 4 has a telephone network 41, and this telephone network 41
has a transmitting terminal 42, a receiving terminal 43, and a central office line terminal 44.

Note that the telephone comparison section 17 and the receiving circuit switching section 15 operate when the output voltage of the power storage section is higher than the output voltage of the rectifier circuit.
This is an example of a receiving circuit switching means that switches a receiving signal from a telephone circuit network to be sent to a telephone receiver without passing through a receiving amplifier.

Next, the operation of the above embodiment will be explained.

First, the operation when the call is in progress and is not on hold will be described.

Direct current from the telephone office 6 is sent to the rectifier circuit 13 via the telephone circuit network 41 via the transmitting terminal 42, the polarity of the direct current is matched, and the direct current is supplied to the constant current/constant voltage circuit 14. The constant current/constant voltage circuit 14 is connected to the transmitting amplifier circuit 11. A constant DC voltage is supplied to the receiving amplifier circuit 12. Therefore, even if the line resistance from the telephone network 41 to the telephone office 6 is large, the amplification factor of the receive amplifier circuit 12 can be maintained at a predetermined value. Here, when the person handling the reception desk (hereinafter referred to as "handler") speaks into the transmitter 2, the voice is converted into an electrical signal,
This converted signal is transmitted into the transmitter/receiver circuit 1, amplified at a constant amplification factor by the transmitter amplifier circuit 11, and transmitted to the telephone line 5 via the telephone network 41 through the transmitter terminal 42. Note that a part of the DC output of the rectifier circuit 13 charges the power storage unit 16 and is supplied to the booster circuit 18 .

On the other hand, the voice signal of the other party comes from the telephone line 5, is transmitted to the receiving terminal 43 via the telephone circuit network 41, is input to the receiving amplifier circuit 12 of the transmitting/receiving circuit section 1, and is input to the receiving amplifier circuit 12 in the receiving amplifier circuit 12. It is amplified by the amplification factor and reaches the ear of the operator from the handset 3. Since the call is not on hold, the output voltage of the rectifier circuit 13 and the output voltage of the power storage unit 16 are the same, and this state can be expressed as a voltage. Comparison unit 17 detects the logical value “O”
is output to the receiving circuit switching section 15. In response to this logical value "0", the receiving circuit switching unit 15 sets its control signal to "0", connects its switching contact 153 to the fixed contact 151, and the audio signal amplified by the receiving amplifier circuit 12 is transmitted to the receiver 3. sent to.

Next, the operation when a call is put on hold during a call will be explained.

When the caller uses the call hold function built into the reception desk 4 during a call, the DC power from the central office 6 is connected to the transmitter terminal 4.
However, in this case, the signal from the telephone line 5 is sent directly from the receiving terminal 43 to the receiving circuit switching means 15 without passing through the receiving amplifier circuit 12. , reaches the handset 3 and reaches the operator's ears.

That is, since the call is on hold, the direct current from the telephone line 5 is not supplied to the transmitter terminal 42, so the rectifier circuit 1
The output voltage of No. 3 becomes ov.

Method 1: During a normal call, the charged power storage unit 16 outputs a charging voltage, so the output voltage of the power storage unit 1 is higher than the output voltage of the rectifier circuit 13.
6 becomes high, this state is detected by the voltage comparator 17, and the voltage comparator 17 outputs a logical value rlJ to the receiving circuit switching unit 15. In response to this logical value "1", the receiving circuit switching unit 15 sets the control signal to "1" and connects the switching contact 153 to the fixed contact 152. Therefore, the received call signal from the telephone network 41 is sent to the handset 3 without passing through the received call amplifying section 12, and therefore, it is possible to monitor the received call even when the telephone is on hold.

FIG. 2 is a circuit diagram showing the above embodiment in more detail.

In FIG. 2, the amplifiers 11a and 12a are as follows:
For example, Motorola's operational amplifier MC34119,
The transistors 14a and 14b are, for example, transistors 23C1815, and the analog switch 15a is, for example, an analog switch TL191.
As an example of the capacitor 16a of the power storage unit 16, for example, a super capacitor of about 1F, and as the booster circuit 18a, for example, a DC-DC converter MA manufactured by Maxim Corporation is used.
X644 can be used.

Further, instead of comparing the output voltage of the rectifier circuit 13 and the output voltage of the power storage unit 16, the voltage comparison unit 17 compares the output voltage of the constant current/constant voltage circuit 14 with the output voltage of the constant current/constant voltage circuit 14 corresponding to the output voltage of the rectifier circuit 13. , the output voltage of the booster circuit 18 corresponding to the output voltage of the power storage unit 16 is compared.

Furthermore, a variable resistor 12b is provided in the feedback loop of the amplifier 12a in the receiving amplifier circuit 12,
When installing the telephone transmitting/receiving amplifier circuit of the above embodiment, the variable resistor 12b is connected to the receiving amplifier circuit 12 according to the level of the receiving signal transmitted through the telephone port 115 (depending on the magnitude of the line resistance). This is to adjust the amplification factor. Note that instead of adjusting the amplification factor with the variable resistor 12b, AGC (
An automatic gain control) circuit may also be provided.

Further, in FIG. 2, a latching relay or the like may be used instead of the analog switch 15a, and voltage may be applied from the booster circuit 18 to the transmitting amplifier circuit 11 and the receiving amplifier circuit 12. The logic values in the voltage comparison section 17 and the receiving circuit switching section 15 may be reversed to those described above, and in this case, an inverter is inserted to perform the same operation as described above.

[Effects of the Invention] According to claim (1), even if the line resistance from the telephone circuit network to the telephone office is large, the amplification factor of the receiving amplifier circuit can be maintained at a predetermined value.

Moreover, according to claim (2), it is possible to monitor incoming calls even when the call is on hold.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a circuit diagram showing the above embodiment in more detail. FIG. 3 is a diagram showing an example of the circuit configuration of a headset used in a conventional telephone reception desk. Fig. 1 1... Sending amplifier circuit, 2... Receiving amplifier circuit, 3... Rectifier circuit, 4... Constant current/constant voltage circuit, 5... Receiving circuit switching section, 6...・Power storage unit, 7... Voltage comparison unit.

Claims (2)

[Claims] (1) In a telephone transmitting/receiving amplifier circuit having a rectifying circuit that rectifies power from the office line, a transmitting amplifier section, and a receiving amplifier section, the constant current/constant voltage circuit is supplied with power from the rectifying circuit. A transmitting/receiving amplifier circuit for a telephone, comprising a constant current/constant voltage circuit that supplies a constant current and a constant voltage to the transmitting amplifier section and the receiving amplifier section. (2) In claim (1), a power storage unit that is charged with power from the rectifier circuit; and when the output voltage of the power storage unit is higher than the output voltage of the rectifier circuit, an incoming call signal from the telephone network is provided. A transmitting/receiving amplifier circuit for a telephone, comprising: receiving circuit switching means for switching to transmit the signal to the handset without passing through the receiving amplifier section.