A 50 Gb/s PAM‐4 VCSEL diode driver in 90 nm CMOS technology

In this article, a broadband vertical cavity surface emitting laser (VCSEL) diode driver circuit has been implemented in TSMC 90‐nm complementary metal‐oxide‐semiconductor technology. The laser diode driver (LDD) circuit includes a pre‐amplifier, a post‐amplifier paralleling with a differentiator, and a current steering circuit. The input to the LDD can be two 25 Gb/s nonreturn to zero voltage signals, which can thereby generate a 50 Gb/s four‐level pulse amplitude modulation (PAM‐4) current signal to drive a VCSEL diode. Using the LDD chip on a printed circuit board, clear PAM‐4 eye diagrams corresponding to 25, 40, and 50 Gb/s can be measured to verify the performance of the LDD chip. The VCSEL LDD chip has been applied in the optical transmitter for short‐reach transmissions.