Direct Eye Diagram Optimization for Arbitrary Transmission Lines Using FIR Filter

A new design algorithm, which directly optimizes the eye diagram using the finite impulse response (FIR) filter as transmitter pre-emphasis, is proposed to counteract the intersymbol interference (ISI) in the high-speed data transmission. To start with, this paper presents a fast eye diagram analysis which relates to the step response of the transmission line system. It is found that not only the frequency-dependent loss but also the multiple reflections due to impedance mismatch contribute much to ISI. A systematic method is then proposed to efficiently design FIR filter for best eye diagram improvement. The optimal set of tap coefficients and tap numbers are determined by direct search method according to the required specifications on eye mask for different applications. Subsequently, the equalization results for unterminated and lossy lines are given to demonstrate the remarkable mitigation of the ISI effects incurred by multiple reflections and frequency-dependent loss. Experimental results are also presented to validate the efficiency of the proposed method.