A 50 Gb/s PAM-4 VCSEL Transmitter With 2.5-Tap Nonlinear Equalization in 65-nm CMOS
- Resource Type
- Authors
- Wayne V. Sorin; Binhao Wang; Michael Tan; Samuel Palermo; Abhinav Tyagi; Sagi Mathai; Kunzhi Yu; Takayuki Iwai
- Source
- IEEE Photonics Technology Letters. 30:1246-1249
- Subject
- Computer science
Bandwidth (signal processing)
Transmitter
02 engineering and technology
Optical modulation amplitude
Atomic and Molecular Physics, and Optics
Electronic, Optical and Magnetic Materials
Vertical-cavity surface-emitting laser
Nonlinear system
020210 optoelectronics & photonics
CMOS
0202 electrical engineering, electronic engineering, information engineering
Electronic engineering
Electrical and Electronic Engineering
Circuit complexity
Electrical efficiency
- Language
- ISSN
- 1941-0174
1041-1135
Utilizing four-level pulse-amplitude modulation (PAM-4) with vertical-cavity surface emitting lasers (VCSELs) is challenging due to device nonlinearity and bandwidth limitations. This letter presents a VCSEL-based PAM-4 transmitter that employs a 2.5-tap nonlinear equalizer to compensate for these issues. The transmitter utilizes lookup-table control of a current-mode digital-to-analog converter (DAC) output stage to enable independent equalization coefficients for different PAM-4 symbol transitions. Utilizing half pre-cursor (MSB only), one main, and one post-cursor taps provides a good balance between circuit complexity and performance. Equalization resolution is increased by segmenting the output stage into a 2-bit symbol DAC and a fine 3-bit equalization DAC. Fabricated in GP 65-nm CMOS, the serializing transmitter operates at 50 Gb/s with 3-dBm optical modulation amplitude (OMA) when driving an 11-GHz VCSEL and achieves 5.12 pJ/bit power efficiency.