Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1989-04-14
1990-07-10
Peng, John K.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
3581911, 455164, 455169, H04N 550
Patent
active
049410504
ABSTRACT:
A television receiver has an a.f.c. arrangement for ensuring the correct tuning of a tuner unit (4) which is tuned to the nominal carrier frequency by a tuning voltage (VT). When the tuner unit (4) is incorrectly tuned to the actual carrier frequency, the a.f.c. system operates in a first mode in which a sweep current produced by a current source (15) is applied by way of a closed switch (16) to an a.f.c. capacitor (17) to produce a swept a.f.c. voltage for the tuner unit (4). The sweep direction is controlled by an RS flip-flop (13) by way of a multiplexer (12) in response to voltage comparators (19, 20) connected to the a.f.c. capacitor (17). When the tuning is sufficiently close such that the received transmission can be correctly decoded, the a.f.c. arrangement goes into a second mode in which the output of a frequency demodulator (6) is applied via the multiplexer (12) to control the current source (15) and hence the voltage across a.f.c. capacitors (17). For this second mode gate pulses (G1, G2) from a processor (11) control the multiplexer (12) paths by a monostable (14) and only cause the switch (16) to be conductive during a given portion of each line period.
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Goodman Edward W.
Peng John K.
U.S. Philips Corporation
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