A 56-Gb/s PAM-4 Transmitter/Receiver Chipset With Nonlinear FFE for VCSEL-Based Optical Links in 40-nm CMOS

• Published in: IEEE journal of solid-state circuits 2022-10, Vol.57 (10), p.3025-3035
• Main Authors: Peng, Pen-Jui, Lee, Po-Lin, Huang, Hsiang-En, Huang, Wei-Jian, Lin, Ming-Wei, Juang, Ying-Zong, Tseng, Sheng-Hsiang
• Format: Article
• Language: English
• Subjects: Bit error rate; Chips (electronics); Clocks; CMOS; Decision feedback equalizers; decision-feedback equalizer (DFE); Digital to analog converters; Equalizers; feed-forward equalizer (FFE); four-level pulse amplitude modulation (PAM-4); Light modulation; Modules; Optical transmitters; Phase detectors; photodiode (PD); Photodiodes; Pulse amplitude modulation; Pulse generation; receiver (RX); Symbols; Transceivers; transmitter (TX); Transmitters; Vertical cavity surface emission lasers; Vertical cavity surface emitting lasers; vertical cavity surface-emitting laser (VCSEL); Voltage; Waveforms
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2022.3192711

This article presents a 56-Gb/s four-level pulse amplitude modulation (PAM-4) transmitter/receiver (TX/RX) chipset for optical link. The optical transmitter (TX) adopts a digital-to-analog converter (DAC)-based structure with a two-tap nonlinear PAM-4 feed-forward equalizer (FFE) implemented in the digital domain to compensate for the asymmetric responses from the vertical cavity surface-emitting laser (VCSEL). The 56-Gb/s PAM-4 receiver (RX) is connected to the photodiode (PD) and transimpedance amplifier (TIA) module for optical application. The interconnection loss from the RX chip to the PD+TIA module is compensated by the RX continuous-time linear equalizer (CTLE) and the one-tap decision-feedback equalizer (DFE). The pattern-filter-based bang-bang phase detector in the RX improves the jitter performance. Both TX and RX are fabricated in the 40-nm CMOS. The VCSEL TX demonstrates a 56-Gb/s compensated PAM-4 waveform with −0.9-dBm outer optical modulation amplitude (OMA) while consuming only 97 mW of power (1.73 pJ/b). The RX achieves 10 −12 bit error rate (BER) with 0.08 UI margin under 10-dB interconnection loss while dissipating 278 mW of power (4.96 pJ/b).