Thomas E Olszewski

US Patent:

47394072, Apr 19, 1988

Filed:

Mar 27, 1986

Appl. No.:

6/844685

Inventors:

Walter Mack - Fairfax County VA
Thomas Olszewski - Walkersville MD

Assignee:

Hekimian Laboratories, Inc. - Gaithersburg MD

International Classification:

H04N 514
H04N 544

US Classification:

358188

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.