Analysis of Nonlinear Power Distribution Network and Estimation of Jitter Transfer Functions Based on Output Buffer Pseudo Open Drain Termination

With increasing data rates of links, jitter budget allowable for the channel keeps decreasing, and precisely estimating jitter becomes very important to have confidence in designing a robust communication system. Current analysis of jitter transfer function assumes a linear or approximately linear power distribution network, but the linearity of power distribution network can be distorted by driver states or load conditions at the end of signal channel. In order to estimate power supply induced jitter accurately, both the receiver termination mode and the interconnection parameters of channel should be considered. In this paper, the nonlinearity of power distribution network caused by termination mode and its effect on jitter are discussed. The emphasis is given to the pseudo open drain termination, which is the popular scheme used in DDR4. Then, an analytical calculation method of transfer functions relating power supply noise to jitter is proposed, in which the nonlinear power distribution network model including the output buffers, signal channels, and pseudo open drain terminations is used to derive the analytical expressions. Simulation results demonstrate that the proposed analytical estimation method achieves good agreement with ADS simulated results under a real case power distribution network.