Time dependent, variable amplitude threshold output circuit for

Details Time dependent, variable amplitude threshold output circuit for Time dependent, variable amplitude threshold output circuit for

1989-03-02

1990-05-22

Ng, Jin F.

Telephonic communications

Substation or terminal circuitry

Amplifying

379387, 381 72, 381 94, H04M 160

Patent

active

049283073

ABSTRACT:
A voice signal compression system wherein the compression threshold may be adjusted to a calibrated level. The system includes a variable gain amplifier for amplifying a voice input signal based on the application of a variable control voltage. A driver increases the power gain of the amplified input signal to provide a power-boosted output signal. In addition to applying the power-boosted output signal to an acoustic output transducer, the power-boosted output is also applied both to a peak detecting comparator and to a threshold reset timer. The comparator produces a digital output that triggers an attack/decay timing generator which produces the control voltage for the variable gain amplifier. The comparator initially is set to a high threshold state by the threshold reset timer. As the levels and peaks of the input signal increase, the comparator begins to trigger digital pulses to the attack/decay timer. At the same time, the threshold reset timer begins measuring the duration of the signal which exceeds the threshold of the comparator. If the threshold reset timer detects that the level of the power-boosted output signal exceeds the threshold of the comparator for a preselected time, then the compression threshold of the comparator is switched to a lower level. The threshold remains low until the continuous signal is removed. At this point, the circuit is reset to its normal mode of operation.

REFERENCES:
patent: 4386236 (1983-05-01), Ferrieu et al.
patent: 4536888 (1985-08-01), Wilson

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