DC holding circuit

Details DC holding circuit DC holding circuit

2005-11-22

2005-11-22

Tran, Sinh (Department: 2646)

Telephonic communications

Subscriber line or transmission line interface

Protective circuit

C379S093050

Reexamination Certificate

active

06968055

ABSTRACT:
DC holding circuitry that may be implemented with other parts of a DAA circuit to terminate a telephone connections at the user's end. The DC holding circuitry may be implemented using a synthesized inductor circuit powered by DC termination circuitry of a DAA telephone line circuit to provide quiet current that may be mirrored to provide the DC holding. The DC holding circuitry may be further implemented to actively steer DC holding current into multiple external transistors to share the power burden, and using an op-amp gain/feedback configuration to achieve low noise and distortion without the need for expensive capacitor-based filter and high powered transistor components. Variable biasing and active current steering may be employed to permit one or more external resistor/s to help dissipate power. The disclosed DC holding circuitry may also be implemented with a fast transient network having a single stage of fast transient filtering placed in the input network. A fast off-hook settling circuit block may also be implemented to achieve fast settling times by using an op-amp to clamp the receive pin voltage of a DAA circuit.

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