Allpass forward equalizer for decision feedback equalization

An allpass forward equalizer (APFE) for use with decision feedback equalization (DFE) is described, The APFE has poles, unlike the normally implemented FIR (finite impulse response) forward equalizer; equalizers with poles can provide superior performance or reduced hardware complexity when compared to all-zero equalizers, but can have local optima and are more difficult to design. A theoretical basis for the allpass is presented and a systematic design procedure is described. It is shown that there are no local optima in a sufficient region about the global optimum such that adaptation is feasible. A performance vs. complexity advantage is shown for the APFE relative to the FIR forward equalizer, and implementation as a continuous-time filter is proposed.