A comparison of two types of single flux quantum comparators for a flash ADC with 10 GHz input bandwidth

We compare the SQUID wheel/quantum Flux Parametron (QFP) comparator to a new Rapid Single Flux Quantum (RSFQ) compatible design. Both have been simulated to demonstrate similar to 0.5 ps threshold accuracy which would permit the construction of a flash analog-to-digital converter with six effective bits of resolution at 10 GHz input bandwidth, over three times better than the best performance demonstrated with any technology. At lower input frequencies, both designs have demonstrated that a 10-bit flash ADC is possible. Although simulations of the QFP-based design are more accurate at high signal slew rates due to its symmetry, the RSFQ-based design has a better signal-to-noise ratio and a faster and more flexible clocking scheme which ultimately prove to be more important.