High-efficiency 100-Gb/s 4-Vpp PAM-4 driver in SiGe:C BiCMOS for optical modulators

In this paper, a PAM-4 driver for optical modulators implemented in 130nm SiGe:C BiCMOS technology with f
T
/f
max
of 300/500 GHz is presented. The design comprises a single stage amplifier with built-in 2-bit DAC in a current-mode topology. The driver delivers a maximum differential output amplitude of 4Vpp to a 100-Ohm differential load and features a small-signal bandwidth of 40GHz. Time-domain measurements are performed feeding two inputs with OOK signals of less than 1 Vppd, demonstrating the PAM-4 encoded data signals at the output up to a baud rate of 50Gbaud (100 Gb/s). The total power dissipation of the driver is 390 mW, which translates to an output power to dissipation ratio of 5.1% demonstrating the high efficiency of the driver. To the best knowledge of the authors, this is the first PAM-4 driver in SiGe achieving such high data rate and output voltage, suitable for future 400-Gb/s optical transmitters.