Multiplexing Techniques of Single Flux Quantum Circuit Based Readout Circuit for a Multi-Channel Sensing System

Time division multiplexing (TDM) and code division multiplexing (CDM) have been investigated for multichannel superconductive sensing systems using single-flux-quantum (SFQ) readout circuits. Output data from a superconductive sensor array can be multiplexed using SFQ binary counters, which count the number of SFQ pulses from each sensor, and are transmitted from a low-temperature environment to a room-temperature equipment using a small number of lines. We have estimated and compared the performance of a multichannel superconductive sensing system that employs TDM and CDM on the basis of analog circuit simulation and circuit design results. TDM is useful for reducing the number of lines, but the slew rate of the sensing system decreases with an increase in the number of channels. On the other hand, in the case of CDM, the slew rate of the system does not decrease with an increase in the number of channels. We have designed and tested a 2-channel digital superconducting quantum interference device system that can perform TDM and CDM employing SFQ up/down binary counters. In both circuits, the 16 Φ₀ input waveforms were reconstructed from the measured data, with an error of less than the flux quantum Φ₀.