A 100-Gb/s PAM-4 Optical Receiver With 2-Tap FFE and 2-Tap Direct-Feedback DFE in 28-nm CMOS

Optical receivers (ORXs) with integrated CMOS electronics enable compact, low-power solutions for 400-G Ethernet and co-packaged optics. In this article, we present a 100-Gb/s PAM-4 ORX with TIA and sampler integrated into a single 28-nm CMOS IC. ORX sensitivity is optimized using a low noise, sub-Nyquist bandwidth TIA followed by a mixed signal sampler that includes 2-tap FFE and 2-tap DFE. A distributed current-integrating summer helps meet feedback latency requirements of 50-Gbaud direct-feedback PAM-4 DFE. Measurements characterizing the CMOS linear TIA indicate ~23-GHz trans-impedance (ZT) bandwidth (BW) with- $2.5~\mu \text{A}_{\mathrm {rms}}$ input-referred noise. Optical measurement results at 100 Gb/s show that −8.9-dBm sensitivity is achieved at 2.4e-4 BER with 3.9-pJ/bit energy efficiency.