A 2.05-pJ/b 56-Gb/s PAM-4 VCSEL Transmitter with Piecewise Nonlinearity Compensation and Asymmetric Equalization in 40-nm CMOS

This work presents a quarter-rate 4-level pulse amplitude modulation (PAM-4) transmitter in 40-nm CMOS for vertical-cavity surface-emitting lasers (VCSELs). It adopts a thermometer code-based architecture with a 2-tap feed-forward equalizer (FFE) to independently control the gain and equalization st...

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Bibliographic Details
Published in:Proceedings of ESSCIRC pp. 373 - 376
Main Authors: Chen, Fuzhan, Zhang, Chongyun, Wang, Li, Pan, Quan, Yue, C. Patrick
Format: Conference Proceeding
Language:English
Published: IEEE 11.09.2023
Subjects:
Amplitude modulation
Asymmetric Equalization
Bandwidth
Equalizers
Europe
Optical variables measurement
PAM-4 Transmitter
Piecewise Nonlinearity Compensation
Solid state circuits
Thermometers
VCSEL
ISSN:2643-1319
Online Access:Get full text
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Summary:This work presents a quarter-rate 4-level pulse amplitude modulation (PAM-4) transmitter in 40-nm CMOS for vertical-cavity surface-emitting lasers (VCSELs). It adopts a thermometer code-based architecture with a 2-tap feed-forward equalizer (FFE) to independently control the gain and equalization strength of the top/middle/bottom (T/M/B) data slices for full compensation of VCSEL nonlinearities. Moreover, a pre-emphasis circuit is embedded within the continuous-time linear equalizer (CTLE) not only to mitigate the data eye skew caused by the VCSEL's asymmetric responses to rising and falling transitions, but also to extend the overall transmitter bandwidth. Optical measurement results demonstrate that with the 56-Gb/s PAM-4 data rate and 2.05-pJ/bit efficiency, the proposed piecewise nonlinearity compensation scheme improves the average sub-eye height/width and the ratio-of-level mismatch (RLM) by 14%/12% and 38%,, respectively, and the asymmetric equalization technique reduces the horizontal eye skew by 63%.
ISSN:2643-1319
DOI:10.1109/ESSCIRC59616.2023.10268794