A Novel PAM4 Duobinary Optical Receiver

The great demand of high-bandwidth intra datacenters interconnects motivate the usage of optical links, over the electrical links, as it offers low power and high-speed operation for long distance without intensive equalization. The PAM4 modulation format has become the de-facto for the optical links because of its balance between the bandwidth-efficiency and the signal-to-noise ratio (SNR). In this article, a duobinary PAM4 (DB-PAM4) sampling based optical receiver is presented, achieving data-rate to bandwidth ratio operation of 6.5x which is double the data-rate of traditional PAM4 sampling for the same receiver electrical bandwidth. The DB-PAM4 sampling decodes the received data in the presence of the inter-symbol interference (ISI), resulted from the receiver analog front-end (AFE) bandwidth limitation, instead of cancelling it as in the equalized optical architectures. To achieve this, a DB-PAM4 TX precoder and RX decoder have been utilized to recover the transmitted data in a feedforward manner. A prototype of the receiver is implemented and simulated in 65-nm CMOS technology. Simulation results show 32Gb/s data-rate operation with 5GHz AFE bandwidth with 40mW power consumption resulting in 1.25 pJ/bit energy efficiency.