Differential SFQ transmission using either inductive or capacitive coupling

The bias current requirement for RSFQ circuits is about an ampere per thousand gates. High current increases the thermal load of cables into the cryostat, produces undesirable currents and fields on-chip, and makes efficient power supply difficult. Series-biasing has been proposed, whereby the circuit is divided into blocks powered in series. This requires floating ground planes for each block, and differential signal propagation across ground plane boundaries where the blocks communicate. We have demonstrated transmission of pseudo-random data across a differential link using two distinct approaches, based on magnetic and capacitive coupling. For each circuit, we have measured data rates up to 30 Gb/s and bit error rates down to 10^-10. Bit error rates extrapolate to lower values. Inductive coupling was implemented in TRW´s 4 kA/cm² Nb process, capacitive coupling in TRW´s 8 kA/cm² process.