A 32Gb/s-NRZ, 15GBaud/s-PAM4 DFB laser driver with active back-termination in 65nm CMOS

A 32Gb/s-NRZ, 15GBaud/s-PAM4 configurable DFB Laser Diode Driver (LDD) is presented in standard 65nm CMOS. The driver employs a balanced-input, single-ended-output topology to deliver large current output, and integrates a tunable pre-emphasis to extend the bandwidth. An on-chip active back-termination (ABT) is proposed which absorbs loading reflections without sacrificing the effective modulation current. Directly wire-bonded to a DFB laser chip, the measurement results show 25.78Gb/s NRZ optical eye-diagram with 4dB Extinction Ratio (ER) and a 19.3% eye-mask margin referred to the 100G specification. The LDD delivers 60mA bias and 60mApp modulation current, consuming only 550mW power consumption.