JPH01176148A - Telephone set circuit - Google Patents

Abstract

PURPOSE:To make the distance of a telephone line close equivalently to decrease the distortion up to a remote distance by adding a circuit to revise its bias operating point in response to a line voltage. CONSTITUTION:A revision control circuit 7 revising its operating point is connected to a constant current circuit 5. A voice signal from a line 4 is fed to a base of a transistor(TR) Q2 via a capacitor C3 and a resistor R4 through the circuit constitution above to operate the TR Q2 and a voltage across a Zener diode ZD is decreased more than the Zener voltage VZD. Since the voltage VTR is increased relatiely, margin to the distortion is increased. Thus, the telephone set circuit not causing the voice distortion is formed even at a remote distance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a telephone circuit, and more particularly to a telephone circuit that performs audio distortion correction.

(Conventional technology) An example of a conventional telephone circuit is shown in FIG.

According to the figure, a handset 1 consisting of a transmitter and a handset is connected to a telephone line (hereinafter referred to as line) 4 via a telephone circuit network (hereinafter referred to as speech network) 2 for driving the handset. A constant current circuit 5 is connected in parallel to this line 4, and the constant current circuit 5 is configured to supply DC power VDD from the line 4 to the dial transmission circuit 3 forming a load.

The constant current circuit 5 includes a PNP transistor Q1 whose emitter is connected to the line 4 via a resistor R1 and whose collector is connected to the ground via a Zener diode ZD.The base of the transistor Q1 is connected in series with the line side as the anode. Two connected diodes D1. line 4 through a circuit in which D2 and capacitor C1 are connected in parallel.
It is also connected to ground via a resistor R2. The connection point between the collector of the transistor Q1 and the cathode of the Zener diode ZD becomes the output of the constant current circuit 5.

The output of this constant current circuit 5 is supplied to the dial transmission circuit 3 via a diode D3, and in order to stabilize the supply voltage, a power supply stabilization circuit 6, which is a series circuit of a resistor R3 and a capacitor C2, is connected to the dial transmission circuit 3. connected in parallel. Normally, the constant current circuit 5 uses the transistor Q1 in the saturation region so that it has low impedance in direct current and high impedance in alternating current.

In such a configuration, when line loss increases over a long distance and the line voltage Vt decreases, the voltage VTR between the emitter side and the collector side of the transistor 7 decreases due to the Zener voltage vZD of the Zener diode 8, and the audio signal The maximum amplitude V 2 of the voltage VTR becomes larger than the voltage VTR, and the audio signal is clipped. For this reason, there was a problem in that the voice was distorted during long-distance calls.

(Problems to be Solved by the Invention) As described above, in conventional devices, when line loss increases during long-distance calls, the voltage between the line in the constant current circuit and the terminal of the constant voltage element ■TI? As a result, there is a problem in that the maximum amplitude V of the audio signal is distorted in a region exceeding this voltage VTR. .

The present invention has been made to solve these problems, and an object of the present invention is to provide a telephone circuit that does not cause voice distortion even at long distances.

[Structure of the invention]

(Means for Solving the Problems) According to the present invention, there is provided a telephone circuit network for driving a handset, a dialing circuit for dialing, and supplying DC power from a telephone line to the dialing circuit. In the telephone circuit having a power supply circuit for the telephone line, operating point changing means is provided for changing the bias operating point of the power supply circuit by a control signal corresponding to the audio signal level in the telephone line.

(Function) In the present invention, since the resistance value of the variable resistance circuit constituting the operating point changing means is varied depending on the circuit voltage, the Zener voltage of the Zener diode that determines the bias operating point of power supply decreases and the VTR increases. Therefore, the amplitude of the audio signal is not clipped and distortion is less likely to occur.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

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

Components that are the same as the conventional components shown in FIG. 3 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

Direct current power is supplied from a Zener diode ZD of a constant current circuit 5 through a diode D3 to a speech network 2 for driving a handset 1 consisting of a handset and load circuits such as a dial transmission circuit 3 located in parallel thereto. However, in this embodiment, a change control circuit 7 for changing the operating point of the constant current circuit 5 is connected to the constant current circuit 5. This circuit has a transistor Q2 whose emitter is connected to the cathode of a Zener diode ZD, and a biased voltage is applied to the base of the transistor Q2 from a line 4 through resistors Rs and Re. A capacitor C for passing the audio signal is connected in parallel to the resistor R5, and a resistor R for increasing the impedance to the audio signal is connected to the base of the transistor Q2 between the connection point of the resistors R5 and R6. It is connected to the.

In such a circuit configuration, the audio signal from the line 4 is applied to the base of the transistor Q2 via the capacitor C and the resistor R4, so that the transistor Q2 is operated, and the voltage across the Zener diode ZD is lower than the Zener voltage ZD. It also goes down. Then, since the voltage VTR increases relatively, the margin against distortion increases.

FIG. 2 is a graph showing the operation, with the horizontal axis representing distance and the vertical axis representing voltage. When there is little line loss on a short distance route, the voltage VTR is larger than the maximum amplitude V of the audio signal, so there is no distortion. However, as the distance increases, line loss increases, V+ decreases, and (VL-VP
) decreases, the terminal voltage vZD of Zener diode 8
intersects at point A, and the audio waveform begins to become distorted.

Therefore, by applying the audio signal from line 4 through capacitor 11 to transistor 14, transistor Q2
, the original Zener voltage vZD of, for example, about 4.5V is lowered by, for example, 2.5V, and a Zener voltage v-ZD of about 2V is obtained.

As a result, the Zener voltage V″2 decreased as shown in the figure.
．． Point B where and (V t, V p ) intersect is an improved distortion point. Therefore, it can be seen that the distance at which distortion occurs increases.

In the above embodiments, the operating point of the power supply circuit is determined by changing the Zener voltage using a transistor whose characteristics change depending on the line voltage detected by resistance division. A means for changing the bias operating point of the power feeding operation can be used.

〔Effect of the invention〕

As explained above, in the present invention, a circuit for changing the bias operating point according to the line voltage is added to the power supply circuit for supplying direct current power from the telephone line to the dialing circuit. This brings the line closer together, which has the effect of reducing distortion over longer distances than before.

[Brief explanation of the drawing]

FIG. 1 is a configuration circuit diagram showing one embodiment of the present invention, FIG. 2 is a diagram of the operating principle of the present invention, and FIG. 3 is a configuration circuit diagram of a conventional telephone circuit. DESCRIPTION OF SYMBOLS 1... Handset, 2... Speech network, 3... Dial transmission circuit, 4... Line, 5...
・Constant current circuit, 6...Power supply stabilization circuit, 7...Operating point change control circuit, Ql, Q2...Transistor, ZD・
... Zener diode, CI, C2, C3... Capacitor, R1, R2, Rs, R4, R5... Resistor. Applicant's agent Mr. Sato

Claims (1)

[Claims] In a telephone circuit comprising a telephone circuit network for driving a handset, a dialing circuit for dialing, and a power supply circuit for supplying DC power from a telephone line to the dialing circuit, 1. A telephone circuit comprising operating point changing means for changing a bias operating point of the power supply circuit in accordance with a telephone line voltage.