A 56-Gb/s, 6.3-pJ/bit PAM-4 DFB Laser Driver Incorporating Asymmetric Equalization and Integrated CDR in 28 nm CMOS

Yang Min, Nan Qi, Yihan Chen, Yi Zhang, Minye Zhu, Guike Li, Yonghui Lin, Huiyao Peng, Mo Guang, Kaiwen Long, Zhao Zhang, Jian Liu, Nanjian Wu, Jingbo Shi, Yong Chen, Frank F. Shi, Liyuan Liu

Abstract: This article presents a 56-Gb/s distributed feedback (DFB) laser driver integrated with a PAM-4 clock and data recovery (CDR). A mixed-signal digital-to-analog converter (DAC) is adopted for power-efficient linear driving. With the help of the CDR, high-speed PAM-4 input is digitized into thermometer code, which is processed in NRZ format along the data path before summation at the output node. In this way, higher modulation linearity is realized by independently adjusting the weight of each slice. A dc-coupled differential drive stage is devised to improve signal integrity and energy efficiency at high speed. Employing a fractional-UI delay asymmetric feed-forward equalization (FFE) extends the laser’s bandwidth while the nonlinearity is compensated. The proposed driver is fabricated in 28-nm CMOS and co-packaged with a DFB laser diode. Measurement results show the modulated optical output reaches a 56-Gb/s data rate and consumes 353-mW power, thus corresponding to the energy efficiency of 6.3 pJ/bit, including the integrated CDR.

External IDs:dblp:journals/tvlsi/MinQCZZLLPGLZLWSCSL25