Radio Frequency Digital to Analog Converter and Signal Combiner

Modern radio frequency (RF) communication systems require more efficient and flexible use of wider bandwidths at higher carrier frequencies, which can be achieved only by direct digital representation of the RF signal itself. New advances in ultrafast superconductor circuits enable digital-RF technology extending all the way to microwave SATCOM bands (X, Ka, and EHF). Previously, HYPRES built and delivered to US Army CERDEC a 30 Gsample/s superconducting digital-RF X-Band receiver and demonstrated reception from XTAR, DSCS, and WGS satellites. The present project focuses on the development of an RF digital-to-analog converter (RF-DAC) for the corresponding digital-RF transmitter. In Phase I, we designed a chain of digital amplifiers to carry high-speed digital data from cryogenic superconductor rapid single flux quantum (RSFQ) logic to room-temperature, followed by a signal combiner and bandpass filter to produce an analog-RF output suitable for driving a high power amplifier (HPA). In Phase II, we will develop this hybrid superconductor-semiconductor system by designing, fabricating, testing, and demonstrating a Nb superconductor integrated circuit (IC) operating at 4 K and a set of three SiGe monolithic ICs: (1) 4-K pre-amplifier, (2) digital amplifier with re-sampling, and (3) DAC with current-mode signal combining, the latter two operating at ambient temperature.