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A hardware‐efficient slope‐error (SE) algorithm based four‐level pulse amplitude modulation (PAM4) baud rate clock and data recovery (CDR) scheme is proposed. The algorithm uses three adjacent data information to obtain slope information, thus reduces the required error samplers by 75% compared to the widely used baud rate CDR, namely, Mueller Müller (MM) CDR when working at same phase detector (PD) gain. The power efficiency of the CDR loop is improved by 36% compared to MM CDR. The proposed PAM4 baud rate CDR does not bring in extra block except for PD, which makes it easy to be extended from adaptive decision feedback equalisation. A 40 Gb/s PAM4 receiver with the proposed CDR is designed in 55 nm CMOS process. The simulated jitter tolerance of the CDR at high frequency exceeds the SONET OC‐768 JTOL mask by at least 0.35 UI at the bit error rate of 10−12. The CDR loop consumes 106 mW from a 1.2 V supply and occupies an active area of 0.1 mm2. [ABSTRACT FROM AUTHOR]

A 40 Gbps 4‐tap 4‐level pulse amplitude modulation closed‐loop decision feedback equaliser (DFE) is proposed. The DFE adopts a novel high‐speed comparator to resolve the critical timing constraints of the first tap. The comparator decreases the slicing delay by shortening the gap between initial and target voltages. Compared with the existing closed‐loop DFE designs, the proposed scheme relieves timing constraints without complex clock distribution circuits and extra area. Simulations based on the RF‐MOS model verify that the delay of the comparator is improved by 32.8% and the output swing is increased by more than 2.8 times. The proposed DFE which can compensate −9.5 dB channel loss is designed in 55 nm CMOS technology. The power consumption is 67 mW from a 1.2 V supply and the circuit occupies an active area of 0.021 mm2, achieving 1.68 pJ/bit energy efficiency. [ABSTRACT FROM AUTHOR]