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

Abstract

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 2x 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.