Semiconductor automated test equipment (ATE) is widely used for testing components of integrated circuits. To measure the jitter of a clock signal using ATE, the ATE has to provide a precision time measurement system or a repeatable signal edge placement. Generally all time measurement units that can measure the time period can also measure PLL jitter. The accuracy depends on the repeatability and precision of the time measurement unit. It is also possible to measure jitter by analyzing edge placement results. In this case, the accuracy depends on the edge placement resolution and on the edge placement repeatability.
However, sometimes the time measurement system in an ATE is not accurate enough to measure jitter in the low ps range, or there is even no time measurement system available on the ATE. If an ATE does have a time measurement system, it is often the case that there is just one time measurement system that has to be shared between sites for multi-site testing, which makes multi-site testing difficult. Furthermore, on some test systems it is not possible to control edge placement timing precisely and often the accuracy of edge placement is not accurate enough for jitter measurement. Systems having an accurate time measurement system or an accurate edge placement are usually very expensive and often the specified load for the device is not the same as the impedance of the measurement system. This can add jitter and influence the measurement results.