On-Chip Jitter Measurement Using Jitter Injection in a 28 Gb/s PI-Based CDR

We present a technique to measure random jitter in a phase interpolator (PI)-based clock and data recovery (CDR) circuit by injecting a controlled amount of square-wave jitter into its edge clock and monitoring its effect on the autocorrelation function of the CDR's bang-bang phase detector output. Jitter is injected by adjusting the code of the edge PI while the autocorrelation function is measured by on-chip counters. Since the injected jitter only affects the edge clock, the CDR remains operational during jitter injection. Using this technique, the rms relative jitter between the clock and data at the CDR input can be estimated with sub-picosecond accuracy as demonstrated in measurements of a 28 Gb/s half-rate digital CDR fabricated in 28 nm CMOS.