Generation and Distribution of Josephson Junction Clock

One of the crucial factors in achieving high performance of superconducting integrated circuits, such as analog-to-digital converters (ADCs), is sampling using a high-frequency clock source with a low cycle-to-cycle jitter. As the superconductor ADC technology matures toward more complex designs for higher dynamic range performance, the need for synchronous clocking of multiple comparators continues to grow. Since high-frequency external clock sources are expensive and make a significant contribution to the heat load of the system, a high-frequency and low-jitter on-chip clock source using long Josephson junction (LJJ) is considered the preferred long-term solution. Toward that end, we are working on improving an on-chip 110-GHz clock source based on an unshunted LJJ in annular geometry. Minimizing the additional jitter added by each fan-out of the clock signal is the effort's goal. For synchronous clocking of up to three comparators, we compare clock distribution using superconducting passive transmission lines and a new approach using novel active transmission lines. We also introduce a method of synchronizing LJJ clock source with an external stable oscillator by injection locking.