Convergence analysis of a PLL for a digital recording channel with an adaptive partial response equalizer

In this paper, the convergence behavior of the timing phase when an adaptive partial response equalizer and a decision-directed type of phase-locked loop (PLL) are used together in the tracking mode for a digital recording channel is described. The phenomenon of bias in the timing phase when the convergence parameter of the adaptive partial response equalizer and the timing recovery constant of the PLL are not selected properly is introduced. The phenomenon, occurring due to the combining effect of two tracking algorithms for the adaptive equalizer and the PLL are investigated, by computer simulation, and the region of convergence for timing phase recovery is discussed. Also, a method to overcome the phenomenon using a variable step-size parameter is described.