An analytic decision method for the feed-forward equalizer tap-coefficients at transmitter

An approach to determine the tap-coefficients of a feed-forward equalizer (FFE) without the error accumulation is proposed. The simple-minded method of taking the negative values of the pulse response as the FFE tap-coefficients generates the error terms accumulated from the previous time points which are two data-periods ahead or further in the past, irrespective of the number of tap-coefficients. This error accumulation is induced because the added components for FFE compensation also experience the intersymbol interference (ISI). For the channel with the pre-cursor components, the situation becomes worse and the error terms are accumulated from all the previous time points which are one data-period ahead and further in the past. In this work, an analytic method is proposed to decide the FFE tap-coefficients, which guarantees no error terms accumulated from the time points up to the data-period times the number of tap-coefficients. In this way, the accumulated error terms are significantly reduced compared to the simple-minded method. The proposed method was applied to a FR4 PCB transmission line with the length ranging from 40 cm to 100 cm, and with the non-zero pre-cursor components at the data rate of 5 Gbps. The proposed method achieved the voltage eye-opening of 46% and 50% for the 2-tap and 4-tap FFE, respectively, with the channel length of 100 cm, while the simple-minded method gives a zero voltage eye-opening.