Answer 5—The 25-MHz clock is not precisely 25/16 times the 16-MHz clock. It is off by 16 ppm, which creates a “beat” with a 2.5-ms period (400 Hz). Because the 25-MHz clock is used to reclock the variable clock coming from the 16-MHz part of the system, it creates a pattern of phase jitter in the generated sine wave that repeats at a 400-Hz rate.

Contributor: David Tweed

Published September 2003