Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1989-01-30
1990-09-18
Shepperd, John W.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358148, 358149, 331 20, 375120, H04N 504, H04N 512, H03L 700
Patent
active
049582283
ABSTRACT:
An analog-to-digital converter converts an input analog video signal into a corresponding digital video signal. A first input terminal of a phase comparator receives the digital video signal. A loop filter receives an output signal from the phase comparator. A digital-to-analog converter converts an output signal from the loop filter into a corresponding analog control signal. First and second voltage-controlled oscillators generate oscillation output signals having different frequencies respectively which depend on the analog control signal. A switch selects and outputs either of the oscillation output signals. A frequency divider divides a frequency of the selected oscillation output signal into a value corresponding to a horizontal frequency. The frequency divider supplies its output signal to a second input terminal of the phase comparator. A change circuit detects whether or not the output signal from the frequency divider remains out of synchronism with the digital video signal for a time equal to or longer than a reference time, and controls the switch to change the selected oscillation output signal from one to the other when the output signal from the frequency divider remains out of synchronism with the digital video signal for a time equal to or longer than a reference time.
REFERENCES:
patent: 4510461 (1985-04-01), Dickes et al.
patent: 4688082 (1987-08-01), Kato
Matsushita Electric - Industrial Co., Ltd.
Parker Michael D.
Shepperd John W.
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