Electronically-switched multifrequency generator for providing t

Details Electronically-switched multifrequency generator for providing t Electronically-switched multifrequency generator for providing t

1978-09-29

1980-04-01

Moffitt, James W.

H04M 150

Patent

active

041963180

ABSTRACT:
In a multifrequency generator providing tone signaling for a telephone, the common switch functions are performed by solid-state switching circuitry (12). The dc drive current level to the solid-state switching circuitry varies with the loop length of the telephone line such that saturation of switching transistors (405, 409, 410, 508 and 518) contained therein will be maintained on longer loops even with the corresponding decrease in operating current available from a central office. In the speech mode, the appropriate switching transistors are driven with a a high impedance current sources (505-507 and 514-517) thereby preventing an unacceptable shunt degradation of the speech signals. Similarly, in the dial mode, a high impedance current sink (406 and 407) drives the appropriate switching transistors, thus preventing shunt degradation of the tone signals.

REFERENCES:
patent: 3525819 (1970-08-01), Jackson
patent: 3544731 (1970-12-01), Cowpland
patent: 3978295 (1976-08-01), van der Plaats
patent: 4061886 (1977-12-01), Callahan
American Microsystems, Inc., S2559 Digital Tone Generator, pp. 1-12, Jun. 1977.

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