A circuit for on-chip skew adjustment with jitter and setup time measurement

This paper reports a circuit for on-chip skew adjustment with jitter and setup time measurement. A test chip has been fabricated in a 65-nm CMOS process. It successfully measures the random jitter distribution and the relative setup time. This circuit becomes necessary in SoCs because direct measurement cannot be performed by external equipment. Setup time of a D-FF is measured by sweeping over the range of an adjustable input delay line. Its jitter is represented by a Cumulative Distribution Function which is measured by sampling the setup time repeatedly. The skew can be adjusted based on the setup time and jitter determined by our method. Furthermore, this method can be extended for almost any number of Target/Reference Programmable Delay Lines. This system enables designers to adjust skew between the distributed clock paths as well as to measure sub-picosecond level jitter and setup time of D-FFs beyond 10-GHz.