Compare Clock Jitter Using the Same Integration Band and Metric

Two clock sources can advertise very different jitter values because the values describe different measurements. An RMS phase-jitter number integrated over one offset-frequency band cannot be compared directly with a period-jitter or cycle-to-cycle result. Start by making the metric and its conditions explicit.

Read the complete specification row

SiTime’s SiT5187 datasheet lists phase, period and cycle-to-cycle jitter with different conditions, including an integration band or measurement population where relevant. It provides a concrete example of why the unit picoseconds alone does not define a comparable result.

Record clock frequency, output type, supply, load, temperature condition, metric, bandwidth and whether the number is typical or guaranteed. Note how discrete spurs are treated in an integrated phase-noise result. Keep any measurement-floor limitation alongside the number.

Connect the metric to the receiver

Identify the receiving device’s clock requirement and its stated measurement definition. A data converter, timing interface and processor clock input may not use the same jitter criterion. Do not choose whichever supplier metric happens to be smallest.

When evaluating additive jitter through a buffer or clock tree, distinguish the source contribution from the added contribution and the total measured result. Use an appropriate analysis method with its assumptions stated. Avoid arithmetically subtracting unrelated RMS values or mixing different frequency bands.

Compare equivalent measurements

If phase-noise data are available, use the same relevant integration range and treatment of spurs for both candidates. Preserve the underlying trace and calculation settings. A narrower integration window can produce a lower result without any change to the oscillator.

For time-domain metrics, record acquisition length, sample population, trigger or clock-recovery method and instrument setup. Include the actual load and probe arrangement. A clean laboratory output under a different termination may not represent the signal at the receiver pin.

Verify the installed clock path

Measure or otherwise validate the clock at the point relevant to the receiver, accounting for buffers, routing and supply conditions. Compare important operating modes such as active digital traffic or power-state changes. Keep frequency accuracy and duty-cycle requirements separate from jitter when they have independent limits.

The final selection record should show an equivalent metric for each candidate and the receiver requirement it satisfies. Retain any unresolved difference in conditions rather than hiding it in a single comparison column. This makes a low-jitter claim technically meaningful and protects the design from a later substitute chosen only by a smaller number in an unrelated datasheet row.