Time-base error correction

Details Time-base error correction Time-base error correction

H - Electricity

04

N

328/28, 350/38,

H04N 5/92 (2006.01) H03L 7/06 (2006.01) H04N 9/83 (2006.01)

Patent

CA 1117648

ABSTRACT OF THE DISCLOSURE In an automatic phase control circuit having a predetermined lock-in range wherein the oscillating signal produced by the adjustable oscillator of the automatic phase control circuit is used in combina- tion with an input signal to derive a signal whose phase is compared to a reference signal, the phase difference between the derived signal and the reference signal being used as a phase control signal for the oscillator so as to minimize this phase difference and thus lock the phase of the derived signal to that of the reference signal, a method of adjusting the oscillator in the event that the phase relation between the oscillating signal and the input signal is outside the lock-in range. During recurrent intervals, which vary with time base errors in the input signal, the number of cycles of the oscillating signal is counted. The count is examined to deter- mine whether it is within a predetermined range of a predetermined count, and if outside this range, the oscillating frequency of the oscillator is adjusted in a direction to return the count to within this predetermined range. In a preferred embodiment, this automatic phase control circuit is used to eliminate time-base errors in at least the chrominance signal of a composite color video signal. In such an embodiment, the adjustable oscillator is used in a frequency- converter for converting the frequency of at least the chrominance signal from an input frequency to a different frequency, and it is the phase of the frequency-converted chrominance signal which is compared to the reference signal. -1-

312677

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