A 4×32-Gb/s VCSEL Driver with Adaptive Feedforward Equalization in 65-nm CMOS.

In this paper, we present a multichannel vertical-cavity surface-emitting laser (VCSEL) driver for co-packaged optics (CPO) with an adaptive feedforward equalization (FFE) to improve the frequency bandwidth using a simple configuration. The proposed VCSEL driver is designed in a 65-nm CMOS process. The post-layout simulation results show that the modulating operation of the 1060-nm band VCSEL is obtained at 32 Gb/s. The fabricated VCSEL driver is tested by on-wafer probing, and the clear eye opening of the electrical output is observed. All 4 channels operate at 32 Gb/s, and the strength of the FFE can be digitally controlled. Additionally, an energy efficiency (EPB) of 1.56 pJ/b/ch is obtained. The measurement results reveal that our VCSEL driver is suitable for CPO modules from the metrics of the bit rate, EPB, and the occupied chip area.