A New Test Approach to Taking Negative Bias Currents as Optimization Parameters for RSFQ Circuits

The magnetic fields induced by the bias currents and the return currents flowing on a ground plane have a great influence on the performance of complex rapid single flux quantum (RSFQ) circuits. Conventional approach applies equal negative bias currents to the ground contacts adjacent to the bias supply contacts to alleviate this problem, but this strategy may not be optimal when the power supply network is complex. We propose a new test approach to adjusting the negative bias currents independently. By changing the current distribution and thereby altering the spatial distribution of the magnetic field across the chip, this approach can make the circuit work, or make the circuit work more stably. Experimental validation on two 8-bit RSFQ CPUs demonstrated the approach's efficacy: redistributing negative currents restored functionality in a nonoperational circuit and eliminated the intermittent failure in another. These results highlight the critical role of adjusting current distribution in overcoming magnetic interference, offering a practical solution for testing and optimizing the power supply of complex RSFQ circuits where conventional approach falls short.