Abstract
We demonstrate the frequency synchronization of multiple single-flux quantum (SFQ) oscillators with different oscillation frequencies. To synchronize these SFQ oscillators, a common constant bias current is supplied to the SFQ oscillators without any bias resistors. When an SFQ oscillator oscillates at a frequency of f, the average voltage across the Josephson junction comprising the SFQ oscillator is , where is the flux quantum in the superconductor. The bias currents supplied to the SFQ oscillators are redistributed to eliminate the average voltage difference output from the SFQ oscillators. As a result, the oscillation frequencies of all the SFQ oscillators are synchronized. Simulation results indicate that SFQ oscillators with an oscillation frequency difference of more than 50 GHz can be synchronized. We experimentally demonstrate the frequency synchronization of two SFQ oscillators composed of circular Josephson transmission lines. Frequency synchronization is expected to contribute toward the development of a low-power stable clock source stabilizing SFQ circuit operation.
Highlights
Owing to their low-power and high-speed operation, superconducting single-flux quantum (SFQ) circuits [1, 2] show potential for use in next-generation integrated circuit technology in the post-Moore era
We investigate the frequency synchronization of multiple SFQ oscillators for the generation of stable SFQ clock pulse trains
We successfully realized the frequency synchronization of SFQ oscillators with different oscillation frequencies by using the common current biasing
Summary
Owing to their low-power and high-speed operation, superconducting single-flux quantum (SFQ) circuits [1, 2] show potential for use in next-generation integrated circuit technology in the post-Moore era. The generation of a high-frequency SFQ clock pulse train is essential for the high-speed operation of SFQ circuits. To generate high-frequency SFQ pulse trains, SFQ oscillators have been studied as on-chip clock generators (CGs) [1, 3,4,5,6]. 34 (2021) 105004 is reasonable to implement a clock generation circuit on each chip In such systems, the oscillation frequency of all the SFQ CGs must be identical in order to synchronize the entire system. We investigate the frequency synchronization of multiple SFQ oscillators for the generation of stable SFQ clock pulse trains. A detailed circuit analysis and the experimental demonstration of the frequency synchronization of SFQ oscillators are presented
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