Clock Stability
Frequency measurement tracks the minute deviations that occur inside high speed digital clock trees during printed circuit board population. Phase jitter variance quantifies the sample to sample fluctuation of signal edges relative to an ideal reference position. Automated optical inspection equipment cannot detect this timing domain degradation because the physical traces remain intact.
High bandwidth oscilloscopes capture the accumulated timing error across thousands of successive clock cycles.
Sampling Limit
Oscilloscope acquisition memory restricts the total duration over which timing errors can be integrated during testing. Phase jitter variance depends directly on the number of captured waveforms because infrequent low frequency modulation events hide inside short acquisition windows. Board designers specify minimum sample counts to ensure that random thermal noise dominates deterministic interference sources within the acquired data set.
Test engineers adjust trigger thresholds to eliminate baseline trigger wander from the recorded standard deviation calculations.
Clock Tree Failure
Power supply ripple couples directly into phase locked loop circuits and drives the measured timing uncertainty upward. Excess phase jitter variance forces high speed serial receivers out of synchronization during initial link training. Manufacturing lines correct this defect by replacing faulty local voltage regulators with discrete filtering networks near the clock distribution IC.
Proper grounding techniques reduce ground bounce and restore normal timing margins across the entire circuit assembly.
