A 26–28-Gb/s Full-Rate Clock and Data Recovery Circuit With Embedded Equalizer in 65-nm CMOS

This paper presents a power and area efficient approach to embed a continuous-time linear equalizer (CTLE) within a clock and data recovery (CDR) circuit implemented in 65-nm CMOS. The merged equalizer/CDR circuit achieves full-rate operation up to 28 Gb/s while drawing 104 mA from a 1-V supply and occupying 0.33 mm². Current-mode-logic (CML) circuits with shunt peaking loads using customized differential pair layout are used to maximize circuit bandwidth. To minimize the area penalty, differential stacked spiral inductors (DSSIs) are employed extensively. A novel and practical methodology is introduced for designing DSSIs based on single-layer inductors provided in foundry process design kits (PDK). The DSSI design increases the inductance density by over 3 times and the self-resonance frequency by 20% compared to standard single-layer inductors in the PDK. The measured BER of the recovered data by the CDR is less than 10^-12 at 27 Gb/s for 2¹¹-1 400 mV PP pseudo-random binary sequence (PRBS) as input data. The measured rms jitter of the recovered clock and data are 1.0 and 2.6 ps, respectively. The CDR is able to lock to inputs ranging from 26 to 28 Gb/s with 2⁹-1 PRBS pattern. Measurement results show that with the equalizer enabled, the CDR can recover a 26-Gb/s 2⁷-1 PRBS data with BER ≤ 10^-12 after a channel with 9-dB loss at 13 GHz.