Energy Efficient Digital Data Link

Efficiently amplifying the high-speed and low-voltage swing outputs of single flux quantum (SFQ) logic to levels that are suitable for interfacing with room temperature electronics has been a long-standing challenge in the field of superconducting electronics. In this work, we investigate the feasibility of using a lossy passive matching network at 4 K, with a pair of differential 100 low-noise amplifiers heatsunk to 18 K and 50 K stages, respectively. The amplifiers were implemented in a 120 nm SiGe BiCMOS technology. The amplification chain is dc coupled and the small-signal link gain was measured to be approximately 48 dB. The power consumption of each of the two amplification stages was 6.3 mW. The chain was measured at 21 K using a high-speed differential nonreturn-to-zero signal having amplitude commensurate with what one would expect from a superconducting circuit, and clean eye diagrams were observed for data rates as high as 30 Gb/s. The chain was also measured when driven from an SFQ/dc interface, with the first gain stage heatsunk to 9 K. In this configuration, clean eye diagrams were observed to 5 Gb/s, with the speed limitation being related to packaging parasitics.