1983-07-15
1985-05-07
Rubinson, Gene Z.
179100L, 179 16F, H04M 176
Patent
active
045159963
ABSTRACT:
A telephone speech circuit includes an integrated circuit (5) powered by the exchange battery via the subscriber's line. The speech circuit includes an earpiece amplifier (25) and a microphone amplifier (26) whose gains are controlled as a function of the length of the subscriber's line. The voltage on pin 7 which is dependent on the line current and hence the line length is compared with a reference voltage on pin 8 which is derived from the forward voltage drop of a diode connected to pin 8 (FIG. 1). A voltage representative of that on pin 7 is derived from a d.c. level shift circuit (27) and applied to the input of an amplifier (28). The reference voltage on pin 8 is applied to the input of an amplifier (29). The outputs of the amplifiers (28) and (29) are compared in a comparator (30) whose output is coupled to gain control inputs of the amplifier (28), the microphone amplifier (26) and the earpiece amplifier (25).
REFERENCES:
patent: 3745261 (1973-07-01), Friedman
Briody Thomas A.
Dwyer James L.
Rubinson Gene Z.
Streeter William J.
U.S. Philips Corporation
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