A related art PAM-4 driver for an electro-absorption modulator (or “EA modulator”, or “EAM”, or simply “EA”) may consist of a digital to analog converter (DAC) and linear amplifier, as shown, for example, in FIG. 1. Highly nonlinear devices like EA modulators (40% THD typical) can be linearized with predistortion using a 2 bit to 6 bit lookup table and high speed DAC to drive a linear amplifier. To keep power dissipation low, the lookup table and DAC may be integrated in CMOS, but to provide sufficient drive amplitude the linear amplifier may be a biCMOS or InP circuit. Such implementations may consume 500 mW-1000 mW of power. Everything could be integrated in biCMOS, but the power dissipation, if this were done, would be much larger. Implementation of this architecture in CMOS is impractical for high data rates such as 56 Gbps, because CMOS circuits capable of operating at this speed can only support Vds and Vgs of 1 V or less. EA's require 2 V drive for good performance. And obtaining linearity in CMOS is difficult without large devices to generate high transconductance, but this leads to devices with high parasitic capacitance, which limits the bandwidth.
Thus, there is a need for an improved driver for an optical modulator.