Multi-level decision feedback equalization with clock recovery

Analytical expressions are developed to describe the dynamic response of the phase detector in multilevel decision feedback equalization (MDFE). First, it is shown that high density recording channels using a 2/3(1,7) run-length code are bandlimited, so that the Nyquist sampling criterion is satisfied. Consequently, the phase-locked loop (PLL) can be analyzed using sin x/x interpolation between samples of the equalized response. Analytical expressions are derived for determining the gain of the phase detector for MDFE, when the PLL uses a stochastic gradient algorithm. However, this approach is not attractive from an implementation standpoint. A simpler strategy in which the timing phase is only updated on certain signal trajectories is presented. The cost of using this simpler phase detector is timing jitter.<
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