42 GBd 3-bit power-DAC for optical communications with advanced modulation formats in InP DHBT

A 3-bit power-DAC was designed and fabricated in 0.7 µm InP double-heterojunction bipolar transistor (DHBT) technology. An 8-level differential output signal with 3.6 Vpp amplitude was measured at symbol rates in the range of 40 GBd. The circuit combines DAC and driver functions allowing to directly drive a modulator without need for a linear amplifier. This compact IC solution is suitable for transmitters with advanced modulation formats like 64-QAM operating at high symbol rate.