Multi-Input SFQ Multiplexers

A multiplexer is a digital structure that controls signal flow, selecting among multiple inputs to produce a single output. A two-input to one output (2:1) multiplexer is commonly used in single flux quantum (SFQ) systems. When three or more inputs to one output are required, 2:1 SFQ multiplexers are typically cascaded to create a multiplexer tree. A multi-input SFQ multiplexer comprising both a three-input (3:1) and four-input (4:1) to one output SFQ multiplexer is presented. These multiplexers require fewer control signals without cascading multiple 2:1 multiplexers. This SFQ circuit function is achieved using an XOR gate, AND gate, NOR gate, non-destructive read out cells, splitters, and confluence buffers for the 3:1 multiplexer. The XOR gate in the 3:1 multiplexer is replaced with two gates that distinguish between the 01 and 10 control signals. The circuit topologies are presented, and the performance and control signals are compared with a conventional 2:1 multiplexer tree and an individual input control multi-input multiplexer. A combination of 2:1, 3:1, and 4:1 multiplexers is proposed to achieve higher performance, leveraging the advantages of each type of multiplexer. A speed increase of 36% and an 83.6% reduction in the number of control signals in a 54:1 multi-input SFQ multiplexer are demonstrated using the combined multiplexer tree.