A Differential Optical Receiver With Monolithic Split-Microring Photodetector

This paper presents a high-sensitivity, fully differential (FD) optical receiver (RX) for high-density system-on-chip applications. The high digital activity prominent in such applications creates common-mode and power-supply noise, which degrades the optical RX sensitivity. To suppress these noise sources and enhance the RX sensitivity, an optical RX is proposed that realizes FD operation by using a new resonant split-microring photodetector. The complete RX is implemented in a 45-nm SOI CMOS with no process changes. When aptly biased, the detector outputs FD photocurrent with <±0.3% splitting error. It has 0.52-A/W responsivity and a bandwidth of 5.0 GHz. The RX circuit is optimized to achieve BER < 10 ⁻¹² at 12 Gb/s with an optical modulation amplitude (OMA) sensitivity of −18.2 dBm while consuming 7 mW. Compared with a conventional single-ended RX on the same test-chip, the proposed RX improves sensitivity from 13 to 7.9 $\mu \text{A}_{\mathrm {pp}}$ without reducing the bandwidth or significantly impacting the RX energy efficiency.