US 4,700,217 AGranted

Chrominance signal phase locked loop system for use in a digital television receiver having a line-locked clock signal

AssigneeRCA Corporation

InventorsAlvin R. Balaban, Walter H. Demmer, Leopold A. Harwood, Chandrakant B. Patel

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Abstract

A digital television receiver which uses a line-locked clock signal employs chrominance signal demodulation circuitry which produces a digital oscillatory signal that is locked in phase to the color reference burst signal component of the incoming video signals. An analog voltage controlled oscillator generates an oscillatory signal having a frequency of approximately twice the color subcarrier frequency. This signal is combined with the composite video signals and the combined signal is digitized by an analog to digital converter. The digitized oscillatory signal is separated from the combined digital signal and is used to synchronize a digital phase locked loop. The digital phase locked loop generates two quadrature phase related signals having frequencies that are one-half the frequency of the analog oscillatory signal. These two signals are used to synchronously demodulate the chrominance signal components of the incoming video signals to obtain two quadrature phase related color difference signals. The control signal for the voltage controlled oscillator is generated by subtracting the burst phase of the demodulated color difference signals from a reference phase and integrating the difference.

Claims12

Dependent claims

In a digital television signal processing system including a source of analog composite video signals, occupying a predetermined band of frequencies and having a color reference burst signal component, a source of clock signal, having an indeterminate phase relationship with said color reference burst signal, and an analog to digital converter having an input terminal and an output terminal for generating, at said output terminal a digital signal representing values of an analog signal applied to said input terminal at instants determined by said clock signal, circuitry for developing a digital oscillatory signal having a predetermined phase relationship with said color reference burst signal comprising:

an analog oscillator, responsive to a control signal for generating a variable frequency oscillatory signal having a frequency outside of said predetermined band of frequencies;
means coupled to said source of analog composite video signals and to said analog oscillator for combining the respective signals provided thereby to develop a signal for application to the input terminal of said analog to digital converter;
signal filtering means coupled to the output terminal of said analog to digital converter for attenuating components of the signal provided thereby which represent said composite video signals relative to components which represent said oscillatory signal;
means coupled to said signal filtering means for generating said digital oscillatory signal being locked in phase to the signal provided by said signal filtering means;
and
means, including phase comparison means coupled to said digital phase locked loop and to said source of composite video signals, for generating said control signal, being proportional to the difference in phase between said digital oscillatory signal and said color reference burst signal.

3 more elements

Apparatus comprising:

a source of composite video signals occupying a predetermined band of frequencies and having a chrominance signal component including a color reference burst signal component;
a source of clock signal having an indeterminate phase relationship with said color reference burst signal;
an analog oscillator responsive to a control signal for generating a variable frequency oscillatory signal having a frequency outside of said predetermined band of frequencies;
means coupled to said source of composite video signals and to said analog oscillator for combining the respective signals provided thereby;
analog to digital conversion means coupled to said combining means for generating a digital sampled data signal representing said combined signal at instants determined by said clock signal;
signal filtering means coupled to said analog to digital converter for attenuating components of the signal provided thereby representing said composite video signals relative to components representing said oscillatory signal;
a digital phase locked loop coupled to said signal filtering means for generating a digital oscillatory signal being locked in phase to the signal provided by said signal filtering means;
and
means for generating said control signal including phase comparison means coupled to said digital phase locked loop and to said source of composite video signals for generating a signal proportional to the difference in phase between said digital oscillatory signal and said color reference burst signal.

6 more elements

Dependencies are inferred from the claim text.