Jitter Accumulation in PAM Systems

Abstract

A new approach to the jitter accumulation problem in a chain of regenerative repeaters for pulse amplitude modulation systems is described. In each regeneration section the timing circuit consists of a square-law device followed by a bandpass filter with center frequency close to the transmission rate. It is shown that, from the standpoint of jitter generation and propagation, the timing circuit is equivalent to a low-pass filter driven by the sum of the jitter generated in the previous regenerator plus a noise term. This is actually the jitter propagation mechanism suggested in [6] and referred to as Chapman's model. What makes a difference with the results published in [6] is that in our analysis an expression is given for the spectral density of the noise in the equivalent model in terms of system parameters such as pulse shape, bandpass filter mistuning, offset in the triggering level of the pulse generator, etc. In this way the various jitter sources can be qualified and their effects evaluated.