A 0.875–0.95-pJ/b 40-Gb/s PAM-3 Baud-Rate Receiver With One-Tap DFE

This article presents a 40-Gb/s (25.6-GBaud) three-level pulse amplitude modulation (PAM-3) baud-rate receiver with one-tap decision-feedback equalize (DFE). A baud-rate phase detector (BRPD) that locks at the point with zero first postcursor is proposed. In addition, by reusing the BRPD’s error samplers, a weighting coefficient calibration is presented to select the DFE weighting coefficient that maximizes the top level of the eye diagram, thereby improving eye height across different channel losses. An inductorless continuous-time linear equalizer (CTLE) and a variable gain amplifier (VGA) are also included. The VGA adjusts the output common-mode resistance to control data swing, reducing power consumption when the required swing is small. Furthermore, by using the modified summer-merged slicers, the capacitance from the slicers to the VGA is reduced. Finally, a digital clock/data recovery (CDR) circuit is presented, which includes a demultiplexer (DeMUX) with a short delay time to reduce the loop latency. The 40-Gb/s PAM-3 receiver is fabricated in 28-nm CMOS technology. For a 25.6-Gbaud pseudorandom ternary sequence of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3^{7}$ </tex-math></inline-formula>–1, the measured bit error rate (BER) is below <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-12}$ </tex-math></inline-formula> for channel losses of 9 and 17.5 dB. At a 9-dB loss, total power consumption is 35-mW with a calculated FoM of 0.875-pJ/bit. At 17.5-dB loss, total power consumption is 38-mW with a calculated FoM of 0.95-pJ/bit.