Tektronix, Inc.

Patten A Emmons

Bruce J Penney

Timothy W Slate

A digital phase-locked loop maintains a clock signal in a predetermined phase and frequency relationship with an input video signal having a repeating signal element, such as horizontal sync pulses and/or color burst signals. The clock signal is generated by a voltage controlled oscillator, the frequency of which depends on an input digital control signal. The input video signal is sampled by an analog-to-digital converter at the clock signal frequency to generate a succession of digital words representing the amplitudes of successive samples. A portion of the successive digital words is stored in a memory, the access to which is controlled so that the samples representing the repeating signal element are stored and then read out for processing by a microprocessor. The digital control signal from the microprocessor which is input to the oscillator represents the difference between the actual phase and frequency relationship between the clock signal and the repeating signal element and the desired predetermined phase and frequency relationship so that the oscillator frequency is varied to attach such predetermined phase and frequency relationship.

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Portland, OR, United States of America

Patten A Emmons