Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1988-04-28
1989-08-08
Chin, Tommy P.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
3581911, 455192, 455316, H04N 550, H04B 126
Patent
active
048558354
ABSTRACT:
An automatic fine tuning (AFT) circuit for a CATV receiver system of a double conversion type having a first local oscillator and a second local oscillator and a first mixer and a second mixer respectively supplied with oscillation outputs from the first and second local oscillators is disclosed. A reception signal is sequentially subjected to frequency conversation by use of the first and second mixers so as to attain an intermediate frequency signal of a predetermined value. The AFT circuit includes a control voltage generator for outputting a control voltage which is a function of a frequency fluctuation of the intermediate frequency signal; a selector for selecting either the control voltage or a constant voltage and for supplying the selected voltage as an oscillation frequency control voltage controlling the oscillation frequency of the second local oscillator; an integration unit for integrating the oscillation frequency control voltage so as to produce an integrated control voltage; and a voltage comparator for comparing the integrated control voltage with a reference voltage so as to supply a result of the comparison to the selector. In response to the compare result from the voltage comparator, the selector supplies the control voltage to the second local oscillator when the integrated voltage is higher than the reference voltage and supplies the constant voltage to the second local oscillator when the integrated voltage is lower than the reference voltage.
REFERENCES:
patent: 4388649 (1983-01-01), Harford
patent: 4575761 (1986-03-01), Carlson
patent: 4709407 (1987-11-01), Baba
Alps Electric Co. ,Ltd.
Chin Tommy P.
Shoup Guy W.
Winters Paul J.
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