A 6.25-Gb/s binary transceiver in 0.13-μm CMOS for serial data transmission across high loss legacy backplane channels

A transceiver capable of 6.25-Gb/s data transmission across legacy communications equipment backplanes is described. To achieve a bit error rate (BER) <10^-15, transmit and receive equalization that can compensate up to 20 dB of channel loss is employed to remove intersymbol interference (ISI) resulting from finite channel bandwidth and reflections. The transmit feed-forward equalizer (FFE) uses a four-tap symbol-spaced programmable finite impulse response (FIR) filter followed by a 4-bit digital-to-analog converter (DAC) that drives a 50-Ω transmission line. The receiver uses a half-baud-rate adaptive decision feedback equalizer (DFE) that cancels the first four symbol-spaced taps of postcursor ISI without use of speculative techniques. Both the transmitter and receiver use an LC-oscillator-based phase-locked loop (PLL) to provide low jitter clocks. Techniques to minimize the complexity of the FIR and DFE implementations are described. The transceiver is designed to be integrated in a standard ASIC flow in a 0.13-μm digital CMOS technology. System measurements indicate the ability to transmit and recover data eyes that have been fully closed due to crosstalk and signal loss.