JPH09162972A - Telephone set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain ease of hearing by allowing an adjustment circuit to decrease a level of an input signal based on an output signal in a way that a reception amplifier circuit properly amplifies the input signal even when the level of the input signal is excessive so as to reduce distortion of a voice wave from a receiver. SOLUTION: An adjustment circuit 5 allows a control transistor(TR) 9 to be switched on with a negative half wave output of an AC output of an output signal amplifier circuit 6 when a level of an input signal to a reception amplifier circuit 3 is excessive. Thus, a power supply +B is fed to a base of an input signal level adjustment TR 12, resulting that the TR 12 is switched on. Thus, part of the input signal to the reception amplifier circuit 3 is given to ground via a collector-emitter path of the input signal level adjustment TR 12. Then the input signal level to a reception amplifier circuit 3 is decreased to allow the reception amplifier circuit 3 to properly amplify the input signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telephone that adjusts the level of an input signal from a station line side.

[0002]

2. Description of the Related Art Generally, the listening volume of a telephone becomes smaller as the line length of an office line to which the telephone is connected becomes smaller due to line loss, making it difficult to hear. A telephone having an automatic listening volume control (ALC) function which is designed to be obtained has already been proposed in JP-A-59-95758 and JP-A-61-78254.

In the telephone disclosed in Japanese Patent Laid-Open No. 59-95758, a current detection circuit for detecting a call current from a local line, a telephone circuit for forming a reception amplification circuit for a handset, and a current detection circuit output are used respectively. It consists of an analog switch consisting of multiple switch elements that operate, an amplifier that amplifies the telephone circuit output current, and a plurality of resistors that adjust the output of this amplifier. With this configuration, the receiving volume can be automatically adjusted to a constant level regardless of the magnitude of the call current from the other party. In the telephone disclosed in Japanese Patent Laid-Open No. 61-78254, a direct current flowing in a direct current closed circuit is used to drive a separately provided control transistor, and the output of the transistor serves as a reception amplifier circuit. The gain of the circuit is continuously changed so that the receiving level becomes almost constant, so that a constant receiving level can be obtained regardless of the line loss of the telephone line.

[0004]

[Problems to be Solved by the Invention] Such a conventional AL
In the telephone with the C function, although the reception volume can be controlled from the office line side to a constant level, that is, the adjustment control can be performed according to the line length of the office line, an excessive input signal that exceeds the control range causes an excessive input signal. I can't handle it if given by. In other words, since the telephones described in any of the publications simply control the gain of the reception amplification circuit, which is an amplification circuit connected to the handset, according to the magnitude of the signal from the office line side, the control range is exceeded. If an excessively large input signal that would otherwise be input is input from the station line side, there is a problem in that the reception amplification circuit may not be able to properly amplify the signal and may saturate and the received voice may be distorted.

In the present invention, unlike such a telephone with an ALC function, even if an excessive input signal is input to the receiving amplifier circuit from the office line side, the receiving amplifier circuit can perform an appropriate amplifying operation. As described above, the main problem to be solved is to lower the level of the input signal and thereby reduce the distortion of the output signal of the reception amplifying circuit so that a voice that is easy to hear can be obtained from the receiver.

[0006]

According to a first aspect of the present invention, in a telephone set of the present invention, a receiver amplification circuit for amplifying an input signal from the office line side, and a receiver for converting an output signal of the reception amplifier circuit into voice and outputting the voice. And an adjusting circuit that adjusts the level of an input signal to the reception amplifying circuit, wherein the adjusting circuit comprises:
According to a configuration characterized in that the distortion of the output signal is reduced by lowering the level of the input signal so that the reception amplifying circuit can properly amplify the input signal even when the input signal is excessive based on the output signal. The above-mentioned problems are solved.

In the present invention, preferably, the adjusting circuit has an input signal level adjusting transistor whose collector-emitter path is connected between the reception amplifier circuit input section and the ground through a predetermined DC cutting capacitor. ,And,
Based on the monitoring result that the level of the input signal to the reception amplification circuit becomes excessive, the transistor is switched on and turned on to drop a part of the input signal to the ground. The level of the input signal may be lowered to a range in which the reception amplification circuit can appropriately amplify the level.

In the present invention, it is more preferable that the adjusting circuit performs a switching operation on an output signal amplifying circuit for amplifying an output signal of the reception amplifying circuit and a half-wave waveform side of an AC output from the output signal amplifying circuit. And a control transistor, wherein the control transistor performs a switching operation according to a half-wave waveform side of an AC output of the output signal amplifier circuit, and the switching operation causes the input signal level adjusting transistor to perform a switching operation to turn on. Good.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A telephone according to an embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit block diagram of a telephone according to an embodiment of the present invention. Referring to the figure, reference numeral 1 is a pair of input terminals connected to the office line, 2 is a rectifier circuit for rectifying a received signal from the office line side, and 3 is an input from the office line side rectified by the rectifier circuit. A receiver amplification circuit 4 for amplifying a signal is a receiver for converting an output signal from the receiver amplification circuit 3 into a voice and outputting it. A reference numeral 5 is an adjusting circuit for adjusting a level of an input signal to the receiver amplifier circuit 3.

The adjusting circuit 5 monitors the level of the output signal of the reception amplifying circuit 3, and from the result of this monitoring, the reception line amplifying circuit 3 is saturated and the amplification operation cannot be performed properly because the input signal on the station line side is excessive. In this case, the level of the input signal to the reception amplifying circuit 3 is lowered so that the reception amplifying circuit 3 does not saturate and can perform an appropriate amplifying operation, so that the distortion of the output signal of the reception amplifying circuit 3 is reduced. The adjustment operation is performed so that the voice received from can be easily heard.

Therefore, the adjustment circuit 5 is connected to the output section of the reception amplification circuit 3 and amplifies the output signal of the reception amplification circuit 3, and the base of the output signal amplification circuit 6 is DC. Pnp which is connected via a cut capacitor 7 and whose base emitter is connected via a current limiting resistor 10 to turn on when the negative half-wave waveform of the AC output from the output signal amplification circuit 6 is equal to or greater than a predetermined value. Type control transistor 9 and the base of which is connected to the collector of the control transistor 9 via the current limiting resistor 10 and the emitter of which is connected to the ground, and the collector of which is connected via the DC cut capacitor 11 to the input section of the reception amplification circuit 3. And an npn type input signal level adjusting transistor 12 connected to the.

In the adjusting circuit 5 having such a structure, the control transistor 9 is controlled by the negative half-wave waveform output of the AC output of the output signal amplifying circuit 6 when the level of the input signal to the reception amplifying circuit 3 becomes excessive. Of the input signal level adjusting transistor 12 is turned on by applying the power supply + B to the base of the input signal level adjusting transistor 12, thereby turning on the collector of the input signal level adjusting transistor 12. A part of the input signal to the reception amplifying circuit 3 is dropped to the ground through the signal to reduce the level of the input signal to the reception amplifying circuit 3 so that the reception amplifying circuit 3 can properly amplify.

That is, an input signal from the telephone station input through the input terminal 1 is rectified by the rectifier circuit 2 and then input to the reception amplification circuit 3, and then amplified by the reception amplification circuit 3 and output. The signal is given to the handset 4 and output as voice. Here, when an excessive input signal is input from the station line side, the reception amplification circuit 3 is saturated and the output signal contains distortion, so that the voice from the handset 4 is very difficult to hear. It becomes difficult. Such a state is shown in FIG. 2 in which the horizontal axis represents the output signal level and the vertical axis represents the distortion of the output signal. Note that FIG.
The reason why the distorted waveform has a slope to the left from point A is that the noise level is constant, but the level of the output signal decreases, and the slope to the right from point A has a slope to the right. Is due to the distortion of the output signal because the input signal is excessive as described above. As is clear from FIG. 2, when the input signal on the station line side becomes excessive and the level of the output signal is at point A or higher, the distortion included in it increases sharply. Therefore, if such a distorted output signal is input to the handset 4, the voice waveform at the handset 4 is considerably distorted, and the received voice becomes very difficult to hear.

In the adjusting circuit 5 of the present embodiment, the adjusting circuit 5 is provided between the input section and the output section of the reception amplifying circuit 3, and when the input signal from the station line side is excessive, the reception amplifying circuit 3 is provided. By adjusting the level of the input section of the receiver to a small level, the output signal of the reception amplification circuit 3 is prevented from being distorted, and this makes it easy to hear the voice at the receiver 4.

That is, the office-line-side input signal supplied to the input terminal 1 is rectified by the rectifier circuit 2 and then amplified by the reception amplifier circuit 3, and the amplified output signal is received by the receiver 4.
Is input to In this way, the user can hear the voice from the other party through the receiver.

If the input signal on the station line side has a proper level, the output signal from the output signal amplification circuit 6 is amplified even if the output signal from the reception amplification circuit 3 is amplified by the output signal amplification circuit 6 in the adjustment circuit 5. Since the negative half-wave waveform side output of the AC output does not reach the level at which the control transistor 9 is switched, the transistor 9 remains off. As a result, the input signal is not dropped to the ground via the collector-emitter path of the transistor 9, so that all the input signals from the station line side are amplified by the reception amplification circuit 3 and the reception output signal of the reception unit 4 is returned to the reception unit 4. Then, the sound will be output.

However, in the case where the input signal from the station line side becomes excessive and the reception amplifying circuit 3 is saturated, the negative half of the AC output from the output signal amplifying circuit 6 in the adjusting circuit 5 is obtained. The waveform output reaches a level at which the control transistor 9 is switched, which causes the control transistor 9 to perform a switching operation and turn on. As a result, the power supply + B is applied to the base of the input signal level adjusting transistor 12, and as a result, this transistor 12 also performs a switching operation, and a part of the input signal that should be applied from the rectifier circuit 2 to the reception amplification circuit 3 is for DC cutting. Since it is dropped to the ground through the collector-emitter passage of the capacitor 11 and the adjustment transistor 12, the level of the input signal to the reception amplification circuit 3 becomes proper, so that the reception amplification circuit 3 can properly amplify the input signal. Become. Therefore, the distortion of the output signal from the reception amplification circuit 3 is reduced, and the sound from the reception unit 4 becomes an appropriate amount of sound with little distortion, which is very easy to hear. That is, as shown in FIG. 3, in the present invention, the distortion is small even when the level of the output signal of the reception amplifying circuit 3 becomes the point A or higher.

In the above-described embodiment, a resistor or the like is appropriately provided between the input section of the reception amplification circuit 3 and the ground, and the collector-emitter passage of the input signal level adjusting transistor 12 inserted between them is provided. It may be possible to adjust the level of the input signal dropped to the ground via the input signal. Further, the output signal amplifier circuit 6 may use an operational amplifier circuit or another amplifier circuit.

[0020]

As described above, according to the present invention as set forth in claim 1, a receiver amplification circuit for amplifying an input signal from the office line side, and a receiver for converting an output signal of the reception amplifier circuit into voice and outputting the voice. An adjusting circuit that adjusts the level of the input signal to the reception amplifying circuit, wherein the adjusting circuit adjusts the level of the input signal even when the input signal is excessive based on the output signal. Since the distortion of the output signal is reduced by lowering the output signal so that it can be amplified properly, the receiving amplifier circuit operates properly even if the input signal on the station line side becomes excessive, and the distortion of the output signal As a result, the distortion of the voice waveform of the handset is also reduced, making it easier to hear.

According to a second aspect of the present invention, in the adjusting circuit, the input in which the collector-emitter path is connected between the receiving amplifier circuit input section and the ground through a predetermined DC cutting capacitor is provided. A signal level adjusting transistor is provided, and based on the monitoring result that the level of the input signal to the reception amplification circuit becomes excessive, the transistor is switched on to turn on a part of the input signal to the ground. Since the level of the input signal to the reception amplifying circuit is lowered to a range in which the reception amplifying circuit can properly amplify the signal by dropping it, it is possible to drop part of the input signal to the reception amplifying circuit to the ground with good response. As a result, the degree of distortion of the voice in the handset is reduced at an early stage.

According to the present invention of claim 3, the adjusting circuit amplifies the output signal of the reception amplifying circuit, and a half-wave waveform of an AC output from the output signal amplifying circuit. A control transistor that performs switching operation on the side, the control transistor performs switching operation on the half-wave waveform side of the AC output of the output signal amplification circuit, and the switching operation causes the input signal level adjustment transistor to perform switching operation. Since it turns on, it is possible to effectively drop part of the excessive input signal to the handset to ground, and even if the input signal level adjustment transistor is on, all of the input signal is grounded during that on period. Since it is not dropped, there is no loss of voice in the handset.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a telephone according to an embodiment of the present invention.

FIG. 2 is a diagram showing distortion of an output signal of a reception amplification circuit due to a conventional excessive input signal.

FIG. 3 is a diagram showing distortion of an output signal of a reception amplification circuit due to an excessive input signal in the present invention.

[Explanation of symbols]

 1 Input Terminal 2 Rectifier Circuit 3 Receiver Amplifier Circuit 4 Receiver 5 Adjustment Circuit 6 Output Signal Amplifier Circuit 9 Control Transistor 12 Adjustment Transistor

Claims (3)

[Claims] 1. A receiver amplifying circuit for amplifying an input signal from the office line side, a receiver for converting an output signal of the receiver amplifying circuit into voice, and an adjustment for adjusting a level of an input signal to the receiver amplifying circuit. A circuit, the adjusting circuit lowers the level of the input signal based on the output signal so that the reception amplifying circuit can properly perform an amplifying operation even when the input signal is excessive. A telephone that is characterized by reducing the distortion of. 2. The adjusting circuit has an input signal level adjusting transistor whose collector-emitter passage is connected between the input section of the receiving amplifier circuit and ground through a predetermined DC-cutting capacitor, and The input to the reception amplification circuit by switching the transistor to turn it on based on the monitoring result that the level of the input signal to the reception amplification circuit becomes excessive and dropping a part of the input signal to the ground. The telephone according to claim 1, wherein the signal level is lowered to a range in which the reception amplification circuit can properly amplify the signal. 3. The adjustment circuit further includes an output signal amplification circuit that amplifies an output signal of the reception amplification circuit, and a control transistor that performs a switching operation on a half-wave waveform side of an AC output from the output signal amplification circuit. 3. The control transistor performs a switching operation according to the half-wave waveform side of the AC output of the output signal amplifier circuit, and the switching operation causes the input signal level adjusting transistor to perform a switching operation to turn on. Phone.