A 25-Gb/s, 2.1-pJ/bit, Fully Integrated Optical Receiver With a Baud-Rate Clock and Data Recovery

This paper presents the design of a single-chip, 25-Gb/s optical receiver comprising of a front-end amplifier, a clock and data recovery (CDR), and a 1:4 demultiplexer. Incorporating with an integrating-type receiver front end, a new baud-rate CDR is proposed to achieve both high sensitivity and highly energy-efficient operations. Compared to conventional 2× oversampling CDRs that require edge samples for timing adjustment, the baud rate CDR reduces the number of sampling phases by half to save both area and power consumption. In addition, a hybrid loop filter consisting of analog decimation and digital postprocessing is proposed. It greatly relaxes the speed requirement of an all-digital loop filter while keeping the flexibility of a programmable loop bandwidth. By applying a pseudo random bit sequence (PRBS) 2
³¹
-1 test pattern and using a photo detector whose responsivity is 0.53 A/W, the input sensitivities of the optical receiver at 20 and 25 Gb/s operations are about -13.8 and -8.7 dBm respectively, for a bit error rate (BER) of less than 10
^-12
. The recovered data jitter at the demultiplexer output is about 1.7-ps rms. The measured jitter tolerance (JTOL) exceeds the mask defined by the IEEE 802.3ba standard. Implemented in a 40-nm CMOS process, the chip area is only 0.09 mm
²
. The energy efficiency of the entire receiver is 2.1 pJ/bit at 25-Gb/s operation.