Phase comparison and phase adjustment for synchronization to a reference signal that is asynchronous with respect to a digital sampling clock
First Claim
1. A digital synthesizer comprising:
- a) a digital oscillator clocked by a sampling clock for generating a periodic digital signal;
b) a frequency and phase comparator coupled to the digital oscillator for comparing a frequency and a phase of the periodic digital signal to another frequency and another phase of a periodic reference signal, that is asynchronous with respect to the sampling clock for the periodic digital signal wherein the periodic digital signal has multi bit values at a sampling rate of the sampling clock and wherein the multi bit values represent the frequency and the phase of the periodic digital signal, to produce frequency and phase comparison values; and
c) an arithmetic unit having a first input coupled to the digital oscillator for receiving the multi bit values and a second input coupled to the frequency and phase comparator for receiving the frequency and phase comparison values and adjusting the multi bit values by the frequency and phase comparison values to produce an adjusted periodic digital signal synchronized to the periodic reference signal.
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Abstract
A periodic multi-bit digital signal is synthesized having a frequency that is specified by the frequency of a periodic reference signal that is asynchronous with respect to a sampling clock of the periodic digital signal. In a digital video system, for example, a digital color subcarrier is synthesized and synchronized to a reference frequency of a crystal oscillator that is asynchronous with respect to a digital system clock for the digital video system. The periodic digital signal is generated by an adjustable digital oscillator clocked by the sampling clock. The frequency or phase of the periodic digital signal is compared to the frequency or phase of the periodic reference signal to produce an adjustment value for adjusting the periodic digital signal to synchronize the periodic digital signal with the periodic reference signal. The digital oscillator, for example, generates the periodic digital signal at the sampling rate by periodically incrementing an accumulator with the adjustment value. The frequency or phase of the periodic digital signal is compared to the frequency or phase of the periodic reference signal, for example, by an up/down counter that is incremented or decremented each cycle of the reference signal and is decremented or incremented each cycle of the digital carrier signal to compute the adjustment value.
139 Citations
22 Claims
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1. A digital synthesizer comprising:
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a) a digital oscillator clocked by a sampling clock for generating a periodic digital signal;
b) a frequency and phase comparator coupled to the digital oscillator for comparing a frequency and a phase of the periodic digital signal to another frequency and another phase of a periodic reference signal, that is asynchronous with respect to the sampling clock for the periodic digital signal wherein the periodic digital signal has multi bit values at a sampling rate of the sampling clock and wherein the multi bit values represent the frequency and the phase of the periodic digital signal, to produce frequency and phase comparison values; and
c) an arithmetic unit having a first input coupled to the digital oscillator for receiving the multi bit values and a second input coupled to the frequency and phase comparator for receiving the frequency and phase comparison values and adjusting the multi bit values by the frequency and phase comparison values to produce an adjusted periodic digital signal synchronized to the periodic reference signal. - View Dependent Claims (2, 3)
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4. A method of synchronizing a periodic digital signal to a periodic reference signal that is asynchronous with respect to a sampling clock for the periodic digital signal, said method comprising:
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a) comparing a frequency and a phase of a periodic digital signal to another frequency and another phase of a periodic reference signal that is asynchronous with respect to a sampling clock for the periodic digital signal wherein the periodic digital signal has multi bit values at a sampling rate of the sampling clock and wherein the multi bit values represent the frequency and the phase of the periodic digital signal to produce frequency and phase comparison values; and
b) adjusting the multi-bit values with the frequency and phase comparison values to produce an adjusted periodic digital signal synchronized to the periodic reference signal. - View Dependent Claims (5, 6, 7)
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8. A method of synthesizing a digital color subcarrier, said method comprising:
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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. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. 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:
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(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. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22)
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Specification