JPH01320830A - Impedance matching circuit - Google Patents

Abstract

PURPOSE:To prevent deterioration in the talking quality caused by mismatching by providing an element whose resistance and capacitance are made variable to a balanced circuit network of a bridge circuit forming a telephone speech 10 and providing a circuit controlling automatically the values corresponding to the change in the line impedance. CONSTITUTION:When the bridge circuit 1 is not balanced, and when a signal of audible frequency is sent from an oscillator 17, the level at the receiver input terminal of the bridge circuit 1 is detected by a level comparator 18. Then a gate of a P-channel MOS transistor(TR) resistor 15 used in the nonsaturation region formed in the balanced circuit network 13 is driven by an output signal corresponding to the balance state of the level to vary the resistance of the MOS TR resistor 15. Moreover, the phase of the signal from the oscillator 17 by the line impedance 2 and the phase by the balanced network 13 are compared by a phase comparator 19 and an output signal corresponding to the phase difference varies the capacitance of the MOS capacitor 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an impedance matching circuit, and particularly to an impedance matching circuit for a telephone speech IC.

[Conventional technology]

Conventionally, in this type of impedance matching circuit, a bridge circuit has been configured with a line-side impedance, a balanced circuit network having a fixed resistor and a capacitor, a first resistor, and a second resistor.

FIG. 2 is a circuit diagram of an example of a conventional impedance matching circuit.

As shown in FIG. 2, a bridge circuit is constructed by a line-side impedance 2 with an impedance Zt, a balanced network 5 of an impedance matching circuit, a first resistor 3 with a resistance value R, and a second resistor 4 with a resistance value R2. 1. , constitutes.

The balanced circuit network 5 is composed of a resistor 6 having a resistance value R3, a capacitor 7 having a capacitance C, and a resistor 8 having a resistance value R4.

The transmitter 9 is inserted between the connection node between the line side impedance] and the balanced circuit network 5 and the connection node between the resistors 3 and 4,
A handset 10 is connected across resistors 3 and 4.

This bridge circuit 1a becomes balanced when equation (1) holds.

ZL When the side impedance changes, the impedances no longer match, and the sidetone due to the reflection of the transmitter output due to the mismatch becomes louder.Therefore, when making a call, your voice bounces more or you hear an echo. It has the disadvantage of deteriorating call quality.

[Means to solve the problem]

The impedance matching circuit of the present invention includes a line-side impedance, a balanced circuit network having a MOS transistor resistor operating in a non-saturation region, and a MOS capacitor, a first resistor, and a second resistor. a connection node with a balanced circuit network, the first resistor, and the second resistor;
a bridge circuit having a transmitter output terminal between the connection nodes with the resistor and a receiver input terminal between the first resistor and the second resistor; and an oscillator connected to the transmitter output terminal. and the output level of the signal from the oscillator at the input terminal of the handset, and depending on the comparison result, the MO8
A level comparator that changes the resistance value of the transistor resistor,
and a phase comparator that compares the phases of the signals from the oscillators at the respective receiver input terminals and varies the capacitance of the MOS capacitor according to the comparison result.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

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

As shown in FIG. 1, a balanced circuit network 13 of line side impedance 2 of impedance ZL and impedance ZBN
between the connecting node between the line side impedance 2 and the balanced circuit network 13 and the connecting node between the resistor 11 and the resistor 12. be the transmitter output terminal of the transmitter 9, and the resistor 11 and the resistor 12
a bridge circuit 1 having both ends thereof as the handset input terminal of the handset 10, an oscillator 17 connected to the handset output end, and a level comparator 18 and a phase comparator each having a signal at the handset input end as input. 19.

Further, the balanced circuit network 13 includes a resistor 14 having a resistance value R13, and a P-channel MOS transistor resistor 15 that operates in a non-saturation region controlled by the output of a level comparator 18 to which a resistance value RTN is applied to the gate. It is composed of a MOS capacitor 16 whose capacitance C'v is varied by the output of one phase comparator.

Here, the bridge circuit 1 becomes balanced because equation (2) holds true.

Z t, X R12= Z BNX R11...(
2) If the bridge circuit 1 does not satisfy equation (2) when an audio frequency signal is sent from the oscillator 17, the level comparator 18 detects the level at the receiver input terminal of the bridge circuit 1, and The gate of the P-channel type MOS transistor resistor 15 used in the non-saturation region, which is configured in the balanced circuit network 13, is driven by the output signal corresponding to the balanced state of Make it variable.

Further, the phase of the signal from the oscillator 17 due to the line side impedance 2 and the phase due to the balanced circuit network 13 are detected by the phase comparator 1.
With the output signal corresponding to the phase difference, MO
The capacitance CV of the S capacitor 16 is varied.

In this way, by detecting the level and phase of the signal from the oscillator 17 at the receiver input terminal, the impedance ZBN of the balanced circuit network 13 can be automatically adjusted in response to the change in the impedance ZL of the line side impedance 2. The balance of the bridge circuit 1 can be maintained by changing it to .

〔Effect of the invention〕

As explained above, the present invention provides an element that can vary the resistance value and capacitance value in the balanced circuit network of the bridge circuit constituting the telephone speech IC, and automatically adjusts these values in response to changes in line side impedance. By providing a control circuit to control the bridge circuit, it is possible to maintain the balance of the bridge circuit even if the impedance on the line side changes during a call, thereby preventing reflections of audio signals and excessive sound leakage to the handset due to mismatching. This has the effect of improving call quality by preventing the occurrence of sidetones such as

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of an example of a conventional impedance matching circuit. 1, ]a...Bridge circuit, 2...Line side impedance, 3, 4...Resistance, 5...Balanced circuit network, 6,
7... Resistor, 8... Capacitor, 9... Transmitter,
10...Telephone receiver, 11.12...Resistor, 13...
Balanced circuit network, 14...Resistor, 15...MOS transistor resistance, 16...MOS capacitor, 17...Oscillator, 18...Level comparator, 19...Phase comparator. 7 Futsusso circuit, 2 times Marushu IFA'l inji 5 Rishi Z, Fu branch (I H device, fO intercom, /l /
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Claims (1)

[Claims] MOS operating in line side impedance and non-saturation region
A balanced circuit network including a transistor resistor and a MOS capacitor, a first resistor, and a second resistor, and a connecting node between the line side impedance and the balanced circuit network, the first resistor, and the second resistor. a bridge circuit having a transmitter output terminal between the connection nodes and a receiver input terminal between the first resistor and the second resistor, and an oscillator connected to the transmitter output terminal; a level comparator that compares the output level of the signal from the oscillator at each of the input ends of the handset and varies the resistance value of the MOS transistor resistor according to the comparison result; and a signal from the oscillator at each of the input ends of the handset; and a phase comparator that compares the phases of the MOS capacitor and varies the capacitance of the MOS capacitor according to the comparison result.