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Computer Simulation of Jitter Characteristics of PLL for Arbitrary Data and Jitter Patterns
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences
Publication Date: 1994/06/25
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section of Papers Selected from 1993 Joint Technical Conference on Circuits/Systems, Computers and Communications (JTC-CSCC'93))
Category: Analog Circuits and Signal Processing
PLL, jitter, time-domain simulation, phase detector, NRZ, retiming,
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In order to investigate the jitter characteristics of PLLs for practical applications, we have developed a computer simulation program of PLL, which can deal with arbitrary patterns both of data and jitters, as well as a conceivable nonlinearity of the circuit performance. We used a time-domain method, namely, we solved the state equation of a charge pump type PLL with a constant time step. The jitter transfer characteristics of a conventional PLL were calculated for periodic input data patterns with sinusoidal jitters. The result agreed fairly well with the corresponding experiments. And we have revealed that an ordinary PD (Phase Detector), which detects the phase difference between input and VCO signals at only rising edges, shows the folded jitter transfer characteristics at the half of the equivalent frequency of the input signal. This folded jitter characteristics increases the total jitter for long successive '1' or '0' data patterns, because of their low equivalent sampling frequency, and might increase the jitter even for the random data patterns. Based on simulation results, we devised an improved phase detector for PLL having a low jitter characteristics. And we also applied the simulation to an FDD (Frequency Difference Detector) type fast pull-in PLL which we have proposed recently, and obtained that the jitter of it was smaller than that of a conventional PLL by 25% for PRBS (pseudo random bit sequence) NRZ code.