8. SFQ/DQFP Interface Circuits

The increasing complexity of hybrid superconductive computing systems has made interface circuits between logic families an issue of growing importance. In this chapter, interface circuits between single flux quantum (SFQ) and directly coupled quantum flux parametron (DQFP) logic families to achieve high speed, low power hybrid superconductive computing systems are presented. In the DQFP-to-SFQ interface, margins greater than \(\pm \)20% of the critical current of the JJs, bias currents, and inductances are exhibited. The margins of the excitation current of the DQFP buffer are \(-\)38% and \(+\)35% with the frequency of the excitation current in the range of 2 to 10 GHz. In the SFQ-to-DQFP interface, the margins are greater than \(-\)33% and \(+\)25%. The margins of the excitation current of the DQFP buffer are \(-\)50% and \(+\)20% for frequencies ranging from 2 to 10 GHz. Since no transformers are required, the physical area of the adiabatic portion of the interface circuits is significantly less than existing interface circuits. The SFQ-to-DQFP interface circuit operates at frequencies approaching 20 GHz. These interface circuits therefore exhibit high parameter margins and operating frequencies while requiring significantly less area as compared to existing interface circuits. The interface circuits support the use of both ultra-low power and high speed logic families in complex hybrid superconductive systems.