Impedance matching circuit

Abstract

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.

Inventors

• 👤 Akira Nakajima
• 👤 朗 中島

Bibliographic Details