Design and demonstration of high-functionality logic cells for miniaturization of SFQ switches

We newly miniaturized single-flux-quantum (SFQ) switch circuits for realizing a large-scale switch. A problem in our conventional design is a large size of circuits, because they consist of combine primitive-function logic cells , such as AND, NOT, and so on. To solve this problem, we investigated an approach that uses high-functionality logic cells . As the first step in such a design approach, we designed a new 2:1 multiplexer (MUX) cell, which is a key component in switches. The main features of the MUX cell include nondestructive operation, timing-free inputs, and compatibility with our standard cell library “CONNECT”. We significantly miniaturized the MUX by 67% in comparison to our conventional MUX circuit, which was implemented by combining primitive-function cells. We also designed a 2 × 2 switch using the MUX cell. In comparison to our conventional 2 × 2 switch, the circuit size, the number of Josephson junctions, and the power consumption were reduced by 27%, 30%, and 38%, respectively. The 2 × 2 switch operated at 40 GHz with a bias margin of ±6%.