Dynamic phase offset measurement
View Patent ↗In one embodiment, a method is provided for measuring a dynamic phase offset between a PLL's input clock and the PLL's feedback input clock, wherein the input clock is spread spectrum modulated in a spread spectrum mode and is not modulated in a static mode. The method includes: in the spread spectrum mode, measuring phase jitter between the input clock and the feedback input clock to form a spread spectrum phase jitter measurement; in the static mode, measuring phase jitter between the input clock and the feedback input clock to form a static phase jitter measurement; and comparing the spread spectrum phase jitter measurement to the static phase jitter measurement to determine the dynamic phase offset.
1. A method of measuring a dynamic phase offset between a PLL's input clock and the PLL's feedback input clock, wherein the input clock is spread spectrum modulated in a spread spectrum mode and is not modulated in a static mode, comprising:
in the spread spectrum mode, measuring phase jitter between the input clock and the feedback input clock to form a spread spectrum phase jitter measurement;
in the static mode, measuring phase jitter between the input clock and the feedback input clock to form a static phase jitter measurement; and
calculating a difference between the spread spectrum phase jitter measurement and the static phase jitter measurement to provide the measurement of the dynamic phase offset.
2. The method of claim 1 , wherein the spread spectrum phase jitter measurement is measured over a number of input clock cycles and the static phase jitter measurement is measured over the same number of input clock cycles.
3. The method of claim 2 , further comprising:
determining the number of input clock cycles by selecting the maximum of a predefined number and a number of cycles of the input clock within a period of the spread spectrum modulation.
4. The method of claim 2 , wherein the number of input clock cycles is at least 2000.
5. The method of claim 1 , wherein the spread spectrum phase jitter measurement includes a plurality of spread spectrum phase jitter measurements and the static phase jitter measurement includes a plurality of static phase jitter measurements.
6. The method of claim 5 , wherein a range for the plurality of spread spectrum phase jitter measurements extends from a most positive spread spectrum phase jitter measurement to a most negative spread spectrum phase jitter measurement.
7. The method of claim 5 , wherein a range for the plurality of static phase jitter measurements extends from a most positive static phase jitter measurement to a most negative static phase jitter measurement.
8. The method of claim 1 , wherein measuring the phase jitter in the spread spectrum and static modes comprises measuring the phase jitter with an oscilloscope.
9. The method of claim 1 , wherein measuring the phase jitter in the spread spectrum and static modes comprises measuring the phase jitter with a time interval analyzer.