A 40 Gb/s CMOS Serial-Link Receiver With Adaptive Equalization and Clock/Data Recovery

Abstract

This paper presents a 40 Gb/s serial-link receiver including an adaptive equalizer and a CDR circuit. A parallel-path equalizing filter is used to compensate the high-frequency loss in copper cables. The adaptation is performed by only varying the gain in the high-pass path, which allows a single loop for proper control and completely removes the RC filters used for separately extracting the high- and low-frequency contents of the signal. A full-rate bang-bang phase detector with only five latches is proposed in the following CDR circuit. Minimizing the number of latches saves the power consumption and the area occupied by inductors. The performance is also improved by avoiding complicated routing of high-frequency signals. The receiver is able to recover 40 Gb/s data passing through a 4 m cable with 10 dB loss at 20 GHz. For an input PRBS of 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> -1, the recovered clock jitter is 0.3 ps <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> and 4.3 ps <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> . The retimed data exhibits 500 mV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> output swing and 9.6 ps <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> jitter with BER <10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> . Fabricated in 90 nm CMOS technology, the receiver consumes 115 mW , of which 58 mW is dissipated in the equalizer and 57 mW in the CDR.