How Low is Low Jitter?

Quick Answer: It depends.

The simple concept of the word “jitter” can take on multiple meanings depending on how it is measured and characterized. Oftentimes, it can be helpful to look at a traditional Figure Of Merit in the clock industry, such as integrated phase jitter using no additional filtering in the band of 12kHz to 20MHz, to get a sense of the performance range that is covered by modern clock oscillators. On the Microchip website, we have summarized data on a selection of devices at standard frequencies.

Devices that can be classified as “low jitter” can cover a wide range that goes from 1ps all the way down to 23fs. These numbers are strongly dependent on the details of the measurement, even within the narrow definition of phase jitter that we have established. Further variation in phase jitter would be seen if we superimposed additional filtering on the data beyond that already assumed by the “brick wall” filter used during measurement.

The message here is that benchmarks like phase jitter are useful, but, even then, details about the measurement can lead to a range of results. When comparing clocks that claim “low jitter” performance always keep in mind the differences between what “jitter” actually means and the particulars of how the numbers on data sheets and in electrical specifications were calculated.