Phase comparison and phase adjustment for synchronization to a reference signal that is asynchronous with respect to a digital sampling clock

A method of synthesizing a digital color subcarrier, said method comprising:

• a) generating a periodic digital signal by clocking a digital oscillator with a sampling clock, the periodic digital signal having multi-bit values representing phase of the periodic digital signal;
• b) generating a periodic reference signal asynchronous to said sampling clock;
• c) comparing the phase of the periodic digital signal to phase of said periodic reference signal to produce phase comparison values;
• d) adjusting the multi-bit values with the phase comparison values to produce an adjusted periodic digital signal synchronized to said periodic reference signal;
• and
• e) producing the digital color subcarrier from the adjusted periodic digital signal.

A digital color subcarrier synthesizer in a digital video system, said digital video system having a system clock for clocking logic circuits for processing video samples, said digital color subcarrier synthesizer comprising, in combination:

• (a) a digital oscillator for generating a periodic digital signal synchronous with said system clock, the periodic digital signal having a series of multi-bit values representing phase of the periodic digital signal;
• (b) a local oscillator for generating a periodic reference signal asynchronous with said system clock;
• (c) a phase comparator for comparing the phase of the periodic digital signal to phase of said periodic reference signal to produce phase comparison values;
• (d) an arithmetic unit for adjusting the multi-bit values with the phase comparison values to produce an adjusted periodic digital signal synchronized to said periodic reference signal;
• and
• (e) a sinusoid generator for producing the digital color subcarrier from the adjusted periodic digital signal.