Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1986-03-27
1988-04-19
Chin, Tommy P.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358 23, H04N 514, H04N 544
Patent
active
047394072
ABSTRACT:
A wide-band FM receiver for satellite-transmitted NTSC color television signals includes a novel tracking filter circuit for extending the noise threshold of the receiver. The tracking filter circuit includes a voltage steerable bandpass filter and a feedback control loop that provides a different loop gain for portions of the feedback signal having frequencies corresponding to the spectral components of the chrominance signal and for portions of the feedback signal having frequencies corresponding to the spectral components of the luminance signal. The control loop comprises a loop amplifier, a comb filter and a low-pass filter for separating the feedback signal according to frequency, and two attenuators to allow the setting of different loop gains for the two frequency-separated portions of the feedback signal. The loop gain at frequencies corresponding to the spectral components of the luminance signal is set at a relatively low level to avoid nonlinearities that cause differential gain and differential phase, while the loop gain at frequencies corresponding to the spectral components of the chrominance signal is set at a relatively high level to achieve optimal tracking accuracy and noise threshold extension without introducing significant subjective color distortion.
REFERENCES:
patent: 2976408 (1961-03-01), Colaguori
patent: 3792357 (1974-02-01), Hekimian
patent: 4035730 (1977-07-01), Clayton
patent: 4283739 (1981-08-01), Martinez
patent: 4633315 (1986-12-01), Kasperkovitz
"An Advanced Threshold-Extension Tracking Filter for Satellite Video Reception", by W. M. Rogers, Proceeding of the 1981 IEEE National Telecommunications Conference, Nov. 29-Dec. 3, 1981, pp. E6.5.1-E6.5.7.
"Design and Performance of Phase-Locked Circuits Capable of Near Optium Performance Over a Wide Range of Input Signals and Noise Levels" by R. M. Jaffee and E. Rechtin, IRE Transactions on Information Theory, vol. IT-1, pp. 66-76, Mar. 1955.
"Synchronized Oscillators as F-M Receiver Limiters" by C. W. Carnenan and H. P. Kalmus, Electronics, Aug. 1944.
Mack Walter
Olszewski Thomas
Chin Tommy P.
Hekimian Laboratories, Inc.
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