Room Temperature Interface for RSFQ Digital Signal Processor

This paper describes a cryogenic multi-chip module (MCM) probe for testing of a superconducting hybrid digital signal processor (DSP) capable of 24 giga multiply accumulate operations per second. The probe has 39 data channels with 4 GHz bandwidth, a 30 GHz high speed clock input line, and 48 biasing lines. The MCM interface board features 164 spring finger contacts for a 30 times 30 mm² MCM. The probe has low heatload (0.23 W) and provides good magnetic shielding with residual field equal to 250Phi₀ over a 5 times 5 mm² area. The measured time skew between 20 of the 1200 mm data coaxial lines is about 70 ps. The probe allows synchronous data word transmission at 2 Gbps.

I. Introduction

Room temperature interface is an inherit component of superconducting electronics systems. Implementation of a room temperature interface without significant compromising of the superconducting chip performance is a difficult task. For digital RSFQ circuits in particular, two major factors conspire against any interface solution: high clock rate and low signal level. At the same time, cryogenic temperatures, thermal load, and electro-magnetic shielding must also be met. Currently only two complete systems with RSFQ circuits have been reported, by Hypres Inc. [1] and SRL in Japan [2]. These systems include cryocoolers, cryopackaging, and complete multi-channel high speed room temperature interface.