Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1977-05-03
1978-07-11
Martin, John C.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
325418, 325465, H04N 550, H04B 116
Patent
active
041005783
ABSTRACT:
There is disclosed an AFT summing circuit for a varactor-type tuning system and in particular for such a tuning system including a UHF tuner and a VHF tuner. A tuning voltage derived from a suitable source indicative of the desired channel or station to be tuned is applied to one input of the AFT summing circuit, while an error signal as derived from an AFT circuit is applied to the other input, to be summed together in a manner whereby the effect of the AFT signal may be adjusted without affecting the tuning voltage. The AFT circuit output is applied at a first level when the VHF tuner is operative, and at a second attenuated level when the UHF tuner is operative. In particular, the AFT summing circuit includes first and second impedance elements for applying the AFT circuit output to first and second input terminals of an operational amplifier, and a third impedance element for applying the tuning voltage to the second input terminal. A fourth impedance element is connected in a feedback loop from the output of the operational amplifier to the first input terminal. The values of the first, second, third and fourth impedances Z.sub.1 , Z.sub.2, Z.sub.3 and Z.sub.4 are selected to satisfy the following equation in order that a substantially predetermined gain is provided to the tuning voltage, regardless of the adjustments made to the AFT circuit output: ##EQU1## Further, there is included means for applying a variable control or gain to the correction signal component of the output of the operational amplifier.
REFERENCES:
patent: 3750028 (1973-07-01), Uchida
patent: 3906372 (1975-09-01), Schatter
patent: 3968437 (1976-07-01), Ong
Admiral Corporation
Gable R. Lewis
Marriott Albert G.
Martin John C.
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