Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Patent
1983-06-06
1985-02-05
Ng, Jin F.
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
455165, 455182, 455183, 455192, H03J 702, H04B 126
Patent
active
044981910
ABSTRACT:
A microprocessor controlled phase locked loop tuning system is disclosed which uses a single AFC detector whose threshold is controlled by the microprocessor. The system comprises a microprocessor (10) which provides frequency data to the PLL (11), and this data controls a programmable frequency divider in the PLL which determines the nominal frequency of a VCO (131) in the tuner (13). An AFC detector (141) in the intermediate frequency section (14) provides an AFC voltage output to the single comparator (15). The comparator produces a logic "0" or a logic "1" output to the microprocessor depending on whether the output from the AFC detector is above or below a predetermined threshold. The microprocessor is first operated in a frequency search mode to increase or decrease the frequency of the VCO in predetermined frequency increments depending on the logic state of the output of the comparator (15). During this mode of operation, the microprocessor may be programmed to respond to a change of state of the output of the detector by causing the frequency of the VCO change in the opposite direction to produce a successive predetermined number of detector output state changes and also to cause the VCO frequency changes to be made in smaller increments. After a predetermined number of detector output state changes have been detected, the microprocessor is then operated in a track mode during which time the microprocessor periodically and temporarily changes the predetermined threshold of the detector (15) alternately up and down by supplying pulses to the input of the detector. In this way a "window" is generated to track the tuning frequency.
REFERENCES:
patent: 4280140 (1981-07-01), Skerlos
patent: 4302778 (1981-11-01), Tanaka
patent: 4397038 (1983-08-01), Rzeszewski
patent: 4408349 (1983-10-01), Yukawa
"A Microcomputer Controlled Frequency Synthesizer for TV", by Rzeszewski et al., 1/78.
General Electric Company
Ng Jin F.
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