Nonsaturating interface supply

Details Nonsaturating interface supply Nonsaturating interface supply

1985-10-04

1988-03-15

Myracle, Jerry W.

Telephonic communications

Substation or terminal circuitry

Conversion of signal form

379395, 323223, 323224, 323315, H04M 1900

Patent

active

047318309

ABSTRACT:
An integrated circuit includes an interface circuit for coupling with a relative high-level VOICE circuit and a relatively low-level DIALER circuit to a subscriber line. A first shunt transistor is coupled across the telephone line and has its collector current forced by a current sink driven from the VOICE circuit. A second shunt transistor is coupled in a current mirror configuration to the first shunt transistor and supplies current to the DIALER circuitry. The interface circuit includes a saturation prevention circuit coupled to the current sink and to the second shunt transistor for sensing a tendency of the second shunt transistor toward saturation and for increasing the collector current load on that transistor in response. The saturation prevention circuit includes a voltage offset element and a sensing transistor arranged to form a loop with the collector-to-base junction of the second shunt transistor. As the collector-to-base junction of the shunt transistor approaches a forward-biased condition, the normally nonconducting sensing transistor is biased into conduction so that the collector load on the shunt transistor is increased.

REFERENCES:
patent: 4197425 (1980-04-01), Secrett et al.
patent: 4360710 (1982-11-01), Chaput et al.
patent: 4495382 (1985-01-01), Smith et al.
patent: 4555597 (1985-11-01), Boeckmann et al.
patent: 4639551 (1987-01-01), Kaire

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