JPS6253054A - Amplifier circuit for telephone communication - Google Patents

Abstract

PURPOSE:To compensate level reduction at a high frequency band of a reception signal at increase in the line loss by varying a variable impedance in response to the detection output of a line current detection circuit so as to change the amplification factor at a specific frequency band of a reception amplifier circuit. CONSTITUTION:A detection circuit 6 detecting a line current is provided and variable impedance circuits 38, 48 are provided at least to one of a transmission amplifier circuit 30 and a reception amplifier circuit 40. The impedance of the variable impedance circuits 38, 48 is varied in response to the detection output of the circuit 6 to change the amplification factor at a specific frequency band of the circuit 40 to compensate the level reduction of the reception signal at a high frequency band when line loss is increased. Thus, the increase in the loss at a high frequency band when the line length is long is reduced and the long distance communication with high quality is attained without causing the decrease in the articulation of the talking voice and the increase in the signal error.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in an amplifier circuit for telephone communications, which includes a transmission amplifier circuit and a reception amplifier circuit that operate using DC power supplied from a circuit Jllll19.

[Technical background of the invention]

Conventionally, examples of this type of circuit include the following. Figure 3 shows its configuration, 2a.

2b indicates a line terminal. This line terminal 2a.

On the line side of 2b, there is a series circuit of the transmission signal voltage source 11 (output voltage value et, o) of the other party's telephone and the telephone impedance 12 (impedance value device') in direct current equivalent, and a line impedance 13 (impedance value device') of the line system. value ZL
), a series circuit of a DC power supply 14 (voltage value ET) of the exchange and a line resistance 15 (resistance (!iRt)) are connected in parallel to each other.

On the other hand, on the telephone side of the summation elements 2a and 2b, a transmission amplifier circuit 3, a reception amplifier circuit 4, and a termination circuit 5 are connected in parallel to each other. Of these, the transmission amplifier circuit 3 includes a transistor 31 as a current-voltage converter and an emitter resistor 3.
It consists of an output amplifying section consisting of 2 and a transmitting signal generating section,
This transmitting signal generating section includes a microphone 23, a transmitting amplifier 34 that amplifies the transmitting signal output from the microphone 23, resistors 35 and 36 that determine the amplification degree of the transmitting amplifier 34, and the transmitting transmitting signal generating section. It is composed of a high AC impedance 7!1 source supply circuit 37 that supplies DC voltage to the amplifier 34. The reception amplifier circuit 4 also includes a reception amplifier 41 and a resistor 44.4 that determines the amplification degree of the reception amplifier 41.
5, an N source supply circuit 47 consisting of an island AC impedance that supplies a DC voltage to the receiver amplifier 4], a balance circuit m42 that guides the receiver signal to the receiver amplifier 41, and a receiver signal amplified by the receiver amplifier 41. and a speaker 46 that outputs the audio as audio. Note that 43 is a resistor that takes out a cancellation signal for canceling sidetone from the emitter resistor 32 of the transmission amplifier circuit 3 and introduces it into the reception amplifier 41. Furthermore, the termination circuit 5 includes a termination impedance network 5
1 and a DC blocking capacitor 52, and the terminal impedance network 51 matches the impedance Zr of the telephone with the line impedance ZL. Note that this telephone impedance Zr value is generally set to 600Ω, which is a representative value of line impedance ZL. This is the phone impedance ZT of the other party's phone.
The same applies to EL'.

With this configuration, the transmitting amplifier 34 and the receiving amplifier 41 are brought into operation by DC voltages supplied from the power supply circuits 37 and 47, respectively. When a call is made in this state, the transmitting signal output from the microphone 33 is amplified by the transmitting amplifier 34 and then converted to a voltage eT by the transistor 31 and sent out to the line. It is received (reception level eR').

Also, the transmitting signal sent from the other party's telephone (signal level e)
t') is input from the line terminals 2a and 2b (received signal level eR) and then introduced into the receiving amplifier 41 via the balanced circuit network 42, where it is amplified and output as sound from the speaker 46.

In this way, a call is made between the user's own telephone and the other party's telephone.

[Problems with background technology]

By the way, in general, in such a telephone communication system, the line resistance RT and the line impedance ZL change depending on the line length and line diameter between the telephone and the other party's telephone, and thus the line loss LL also changes. Also, the amount of change in this line loss LL is
It has the property that it is larger in the high frequency band than in the middle and low frequency band, and becomes larger as the frequency becomes higher in this high frequency band. For this reason, in the conventional amplifier circuit described above, when a long-distance call is made, the received signal level in the high frequency range decreases significantly, resulting in an increase in signal errors and a decrease in the clarity of the call voice. There was a drawback that call quality deteriorated.

(Objective of the Invention) The present invention makes it possible to reduce the increase in loss in the high frequency range when the line length is long, thereby providing high-quality long-distance communication without increasing signal errors or deteriorating the clarity of voice calls. An object of the present invention is to provide an amplifier circuit for telephone communication that can perform communication.

[Summary of the invention]

In order to achieve the above object, the present invention focuses on the point that a change in line impedance appears as a change in line current and line end voltage, and provides a detection circuit for detecting the line current or line end voltage, and A variable impedance circuit is provided in at least one of the transmission amplifier circuit and the reception amplifier circuit, and the impedance of the variable impedance circuit is varied according to the detection output of the detection circuit to adjust the amplification degree of the amplifier circuit in a specific frequency band. change,
This compensates for the level drop in the high frequency band of the received signal when the line loss increases.

[Embodiments of the invention]

FIG. 1 shows the configuration of an amplifier circuit for telephone communications in one embodiment of the present invention. In addition, in the same figure, the third
Components that are the same as those in the figures are given the same reference numerals and detailed explanations will be omitted.

A line N flow detection circuit 6 is connected to the emitter of the current-voltage conversion transistor 31 of the transmission amplifier circuit 30.

This line current detection circuit 6 includes a detection resistor 61 and an AC signal bypass capacitor 62, and includes a line current I
This detects the emitter voltage EE which changes proportionally in accordance with L.

In addition, variable impedance circuits are provided in parallel with the resistors 35 and 44 in the negative feedback circuits that determine the amplification degrees of the transmitting amplifier 34 and the receiving amplifier 41, respectively. These variable impedance circuits each include variable resistance circuits 38 and 48 whose resistance values change in inverse proportion to the detected voltage EE of the line current detection circuit 6, and high frequency passing capacitors 39 and 49.

Because of this configuration, the impedances Z35' and Z45' at both ends of each resistor 35.45 of the transmission amplifier circuit 30 and the reception amplifier circuit 40 are respectively expressed as
From this, the voltage amplification degrees AVT and AVR of the transmitting amplifier 34 and the receiving amplifier 41 are expressed as, respectively. Here, the frequencies at which the high-frequency amplification starts increasing are frt-1/2πc 39x R38 fR1-1/2πc 49x R48 for both transmission and reception, and the frequencies at which the increase stops are kC6:
3+Kjt3. Therefore, the variation width of the amplification degree in the high frequency band is ΔAV-20loHfr2 /LrsΔAVR-20 for both transmission and reception.
10CII fR2/fRt.

As is clear from the above, when a long-distance call is made in the circuit of this embodiment, for example, the line current IL decreases in accordance with the line length and wire diameter at that time, and the current value changes to the line current detection circuit 6. is detected as a voltage by the resistor 61. Then, depending on this detection voltage EE, each variable resistance circuit 38.4 of the transmission amplifier circuit 30 and the reception amplifier circuit 40
The resistance values of 8 increase in inverse proportion to the decrease in the line current It, and as a result, the amplification degrees of the transmitting amplifier 34 and the receiving amplifier 41 in the high frequency band increase, so that the transmitting signal in the high frequency band increases. The decreases in the level and received signal level are each compensated for. Therefore, even when making a long-distance call, the level of the high-frequency band component of the received signal can be kept sufficiently high, thereby allowing high-quality calls to be made without causing communication errors or deterioration in the clarity of the call voice. I can do it.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, a variable impedance circuit is provided in both the transmission amplifier circuit 30 and the reception amplifier circuit 40 to vary the degree of amplification, but only one of the transmission amplifier circuit 30 and the reception amplifier circuit 40 has a variable impedance circuit. An impedance circuit may be provided to compensate only the received signal level.

In this way, the circuit configuration can be simplified. Also, if the communication kumite's telephone is fixed,
Only one of the telephones may be provided with compensation means for the transmitting signal level and receiving signal level.

Furthermore, in the embodiment described above, the impedance of the variable impedance circuit is controlled by detecting changes in the line current It, but as shown in FIG. A detection circuit 7 is provided,
By this circuit 7, times I! The impedance of the variable impedance circuit may be controlled by detecting changes in the asthmatic voltage EL. In addition, the range of frequency bands in which the amplification degree is varied, the configuration of each transmitting and receiving amplifier circuit,
The means for varying the degree of amplification, the configuration of the line 'R current or line end voltage detection circuit, etc. can be modified in various ways without departing from the gist of the present invention.

(Effects of the Invention) As detailed above, according to the present invention, a detection circuit for detecting line current or line end voltage is provided, and a variable impedance circuit is provided in at least one of the transmitting amplifier circuit and the receiving amplifier circuit. The impedance of this variable impedance circuit is varied according to the detection output of the detection circuit to change the amplification degree in a specific frequency band of the reception amplifier circuit, thereby reducing the level of the reception signal in the high frequency band when line loss increases. By compensating for this, it is possible to reduce the increase in loss in the high frequency range when the line length is long. It is possible to provide an amplifier circuit for telephone communication that enables long-distance communication.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an amplifier circuit for telephone communications in one embodiment of the present invention, FIG. 2 is a diagram showing the configuration of an amplifier circuit for telephone communications in another embodiment of the invention, and FIG. 3 is a diagram showing the configuration of a conventional amplifier circuit for telephone communications. FIG. 2 is a diagram showing the configuration of an amplifier circuit for telephone communication. 11... Transmission signal voltage source of the other party's telephone, 12... Telephone impedance of the other party's telephone, 13... Line impedance, 14... DC power supply of the exchange, 15...
Line resistance, 2a, 2b... Line terminal, 30... Transmission amplifier circuit, 40... Receiving amplifier circuit, 31... Transistor for current-voltage conversion, 32... Emitter resistance, 3
3...Microphone, 34...Speech amplifier, 41...
... Receiving amplifier, 35.36.44.45 ... Resistor for determining amplification degree, 37.47 ... Power supply circuit, 38.
48... Variable resistance circuit, 39.49... High-pass capacitor, 42... Balanced circuit network, 43... Resistor for sidetone circuit, 46... Speaker, 5... Termination circuit 51
... Termination impedance network, 52 ... DC blocking capacitor, 6 ... Line current detection circuit, 61 ... Resistor for current detection, 62 ... Bypass capacitor, 7.
...Line end voltage detection circuit, 71.72...Voltage dividing resistor,
EL...Line end voltage, IL...Line current, ZL...
・Line impedance, Z position...telephone impedance.

Claims (1)

[Claims] In a telephone communication amplifier circuit comprising a transmitting amplifier circuit and a receiving amplifier circuit operated by DC power supplied from the line side, the transmitting amplifier circuit includes a detection circuit for detecting line current or line end voltage of the line, and a detecting circuit for detecting the line current or line end voltage of the line; Telephone communication characterized by comprising: a variable impedance circuit that is provided in at least one of the circuit and the reception amplifier circuit and that varies the degree of amplification in a specific frequency band of the amplifier circuit in accordance with the detection output of the detection circuit. amplifier circuit.