A 6-bit 56-GSa/s DAC in 55 nm SiGe BiCMOS

We present a 6-bit 56-GSa/s digital-to-analog converter (DAC), implemented in 55 nm SiGe BiCMOS. It consumes 2.36 W of which 0.77 W is utilized in the DAC core. Experiments show an analog 3-dB bandwidth exceeding 28 GHz and an effective number of bits (ENOB) of 3.9. We demonstrate transmission of 112 Gb/s four-level pulse-amplitude modulation (PAM-4) and 168 Gb/s PAM-8 over a channel consisting of an electrical probe and 20 cm RF cables. With pre-equalization compensating the channel loss, we achieve a 0.59 Vpp signal swing.