Modeling and Design Optimization of a Wideband Passive Equalizer on PCB Based on Near-End Crosstalk and Reflections for High-Speed Serial Data Transmission

We propose a closed-form analytic model for the newly presented passive equalizer using near-end crosstalk and reflections on printed circuit board (PCB). The proposed model is developed by using impulse response analysis and the Fourier transform. Based on the model, we propose a design-optimization procedure for the passive equalizer, which achieves eye-opening maximization and ISI minimization in order to maximize the equalization performance and reduce the design cycle. In the proposed optimization procedure, the eye-opening is maximized with a parameter sweep and peak distortion analysis, and the ISI is minimized by the proposed negative ISI cancellation technique. The proposed model and the design-optimization procedure are demonstrated experimentally for a data rate of 16 Gb/s on a 40-cm-long backplane PCB, and they achieve wideband equalization with a significant improvement in the voltage and timing margins of the received serial data.

I. Introduction

Recently, serial interconnect technologies have matured to enable high-speed switched architectures with excellent performance and scalability. Because of the serialization trend, data rates of serial chip-to-chip digital I/O communication channels have increased considerably to over 10 Gb/s [1]. Due to these increasing data rates, high-speed digital I/O signals suffer from frequency-dependent losses on printed circuit boards (PCBs) and at cables [see Fig. 1(a)]. Consequently, ISI problems result, as shown in Fig. 1(b), and there is subsequent degradation of the receiver eye-opening, jitter performance, and voltage margin with increased bit error rate (BER) [2], [3]. Fig. 1.

(a) Frequency-dependent losses of microstrip lines with various lengths on PCB. (b) Illustration of ISI for (top) transmitted signal and (bottom) received signal through a 40-cm-long microstrip line on PCB with a data rate of 16 Gb/s.