Importance

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Abstract

A fast tuning subsystem includes a tuner for selecting a channel, with a voltage controlled oscillator having a control input for determining the channel frequency the tuner selectively receives. A predictor supplies a selected predicted voltage signal from memory to the control input of the oscillator to slew the channel frequency at a rapid slew rate to the frequency corresponding to the selected predicted voltage signal. An error detector generates a tuning error signal indicative of the tuning error of the tuner off the frequency for the selected channel. The tuning error signal is combined with the selected predicted voltage signal to provide a control signal for adjusting the channel frequency to reduce the tuning error. The subsystem also similarly controls the amplitude of the received channel. The tuning subsystem automatically and from time to time changes the signals stored in the memory for respective channels to signals corresponding to the control signals applied after long term feedback. The feedback provides successively a correction mode and a station-keeping mode. The correction mode provides correction of any error in tuning of an acquired channel fast enough that the correction is substantially imperceptible to the eye and any residual error is substantially imperceptible to the eye. The station-keeping mode operates slowly enough to filter out noise and spurious signals and maintain any residual error below a predetermined limit over long periods of time.

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First Claim