High-speed single flux-quantum up/down counter for neural computation using stochastic logic

We propose the high-speed single flux-quantum(SFQ) up/down counter for the neural computation using stochastic logic. Up and down signals are counted by two independent counters, respectively. The proposed counter circuit can count SFQ signals of 50GHz with large operation margins. To realize the up/down counter, we fabricated a 2-bit up counter circuit and a 2-bit down counter circuit as basic blocks by Nb integrated circuits. The low-speed test results of these circuits show correct operations. We also measured dc voltages of Josephson transmission lines to investigate the responses of carry operations for SFQ pulse trains. The results show that the counter circuits have potential to count 144GHz SFQ pulses.