US 5,497,202 A · Automatic digital frequency control circuit

Abstract

An automatic digital frequency control circuit is used for processing a digital video signal. The control circuit includes a phase difference calculator, which samples an analog horizontal sync signal and generates a phase difference value between the corrected phase values with respect to a present scanning line and a phase value of a previous scanning line of which the error values are corrected when a digital horizontal sync signal is obtained, and a phase difference accumulator, which accumulates the phase difference value from the phase difference calculator to a phase difference accumulated value which has been already stored therein. The control circuit also includes an oscillation step corrector, which generates correction step data, a phase value generator, which increases the stored phase value by the corrected oscillation step data whenever the system clock is applied thereto and stores and outputs the increased phase value, and a carrier generator, which generates a carrier having a frequency corresponding to the phase value generated in the phase value generator. It will be noted that since the carrier used for processing the digital video signal is digitally generated, a compact system can be obtained while the difficulty in designing a voltage controlled oscillator which limits digitization of the system is resolved.

Claims18

Dependent claims

An automatic digital frequency control circuit for generating a carrier which is synchronized to a digital horizontal sync signal, said automatic digital frequency control circuit comprising:

a phase difference calculator for calculating and providing a phase difference signal between two adjacent scanning lines in response to an error value representative of an error between digital horizontal sync signal with respect to a present scanning line and a phase value of a previous scanning line;
a phase difference accumulator receiving the phase difference signal for combining the received phase difference signal with a phase difference accumulated value, which has been already stored in said accumulator so as to permit output of a new phase difference accumulated value as the result of an accumulation operation;
an oscillation step corrector generating fundamental oscillation step data, generating correction step data correcting the fundamental oscillation according to the phase difference accumulated value supplied from said phase difference accumulator by using correction step data, thereby generating the corrected oscillation step data;
a phase value generator receiving the corrected oscillation step data, increasing a phase value, which has been already stored responsive to said corrected oscillation data, generating a plurality of phase values for carrier generation with respect to the present scanning line, and supplying respective generated phase values to said phase difference calculator;
and
a carrier generator generating a carrier having a frequency corresponding to each of said respective phase value generated from said phase value generator.

3 more elements

An automatic digital frequency control circuit for generating a carrier which is synchronized to a digital horizontal sync signal, said automatic digital frequency control circuit comprising:

phase difference calculating means for calculating and providing a phase difference signal between two adjacent scanning lines in response to an error value representative of an error between digital horizontal sync signal with respect to a present scanning line and a phase value of a previous scanning line;
phase difference accumulating means receiving the phase difference signal for combining the received phase difference signal with a phase difference accumulated value so as to permit output of a new phase difference accumulated value as the result of an accumulation operation;
oscillation step correcting means for generating fundamental oscillation step data, for generating correction step data for correcting the fundamental oscillation according to said new phase difference accumulated value by using correction step data, and for generating a corrected oscillation step data;
phase value generating means receiving the corrected oscillation step data, for increasing a phase value, which has been already stored responsive to said corrected oscillation data, for generating a plurality of phase values for carrier generation with respect to the present scanning line, and for supplying respective generated phase values to said phase difference calculating means;
and
carrier generating means for generating a carrier having a frequency corresponding to each of said respective phase value generated from said phase value generating means.

3 more elements

Dependencies are inferred from the claim text.

Automatic digital frequency control circuit

Life of this patent

Automatic digital frequency control circuit

Life of this patent

Abstract

Claims18