How to Measure Jitter

Continuous advances in high-speed communication and measurement systems require higher levels of performance from system clocks and references. Performance acceptable in the past may not be sufficient to support high-speed synchronous equipment. Perhaps the most important and least understood measure of clock performance is jitter. One of the main challenges with jitter measurements is that there are currently no established industry standard methods. There are multiple variables to consider, from what test equipment is used to what are the actual test conditions. While JEDEC standards provide definitions and suggested test conditions, there is a lack of consistency between measurements from different testers.

There are three components that remain consistent for all forms of jitter testing: the device under test (DUT), a reference oscillator, and a power supply. A reference oscillator is a vital component for the test setup because the equipment measuring the DUT needs to have a better noise floor than the DUT. Otherwise, the performance of the DUT will be degraded by the noise of the equipment.

Standard measurement equipment (oscilloscopes, counters, signal source analyzers) contain an internal TCXO/OCXO and, for most timing devices, these are sufficient. Microchip’s test equipment uses a low phase noise OCXO locked to an external 10MHz Rubidium clock which is in turn locked to a GPS receiver.