Automatic gain control system for use in positive modulation whi

Details Automatic gain control system for use in positive modulation whi Automatic gain control system for use in positive modulation whi

1992-12-07

1993-12-21

Groody, James J.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358174, 358171, 358156, H04N 552, H04N 510

Patent

active

052725316

ABSTRACT:
An AGC system for use in positive modulation schemes of video signals is provided. The AGC system utilizes an IF amplifier, a demodulator, a video amplifier, a gated amplifier and a peak detector. The gated amplifier has a first, relatively fast, time constant associated therewith. The gated amplifier, which is activated during the time interval that the black voltage appears on the video signal, is responsive to an intial reference voltage and to the video signal for providing an output signal to control the gain of the IF amplifier. The peak detector has a second, relatively slow, time constant associated therewith. The peak detector is used to detect the peak white voltage level of the video signal to adjust the initial reference voltage to account for fluctuations and errors in the peak white voltage level.

REFERENCES:
patent: 2651675 (1953-09-01), Wissel
patent: 2950343 (1960-08-01), Goodrich
patent: 3182123 (1965-05-01), Kao
patent: 3558816 (1971-01-01), Wise
patent: 4234892 (1980-11-01), Mochizuki et al.

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