Concurrent Estimation of a PLL Transfer Function by Cross-Correlation with pseudo-random Jitter

PLL parameters like phase margin influence the overall performance of an IC. For safety-critical ICs, PLL parameters should be measured not only once in production test, but also in the field, preferably continuously, i.e. concurrent to the application mode. The paper proposes a way to measure PLL parameters by adding pseudo-random noise to the clock signal or using a signal that is available anyway e.g. for dithering purposes to avoid spurious tones, and to calculate the cross-correlation of this pseudo-random noise signal and the output signal of the PLL's phase detector. The result of this correlation allows for calculating the PLL's impulse response w.r.t. the phase of its input clock. This impulse response can be used to calculate the phase margin and other parameters of the PLL. Detailed simulation results are presented.