Low Noise SQUID Array Amplifiers for High Speed Applications

Digital signal processing electronics are needed to replace analog circuitries for high-speed applications, such as nuclear physics instrumentation. Superconducting electronics are ideal candidates for these applications, as their speed of operation can easily approach 40 GHz when utilizing small-scale, integrated-circuit fabrication technology. However, output voltage levels in super-conducting logic gates are too low to be instrumented with conventional electronics for further processing. This project will develop a low noise Superconducting QUantum Interference Device (SQUID)-based amplifier, along with associated cooled semiconducting-based amplifier chips, as an interface between high-speed superconducting processing electronics and room temperature digital processing peripheral electronics. In Phase I, SQUID amplifiers were integrated with the outputs of a high performance Analog to Digital Converter (ADC) operating close to 24 GHz clock frequency. The low noise SQUID amplifiers integrated an array of SQUIDs in series utilizing Josephson Transmission Lines (JTLs). The SQUID stack in each amplifier was followed by a high-gain semiconductor amplifier (which accepts an input of ~2mV and generates an output of ~1V) that can be read by standard semiconductor logic circuits for further processing. Since bandwidth associated with JTLs is on the order of tens of GHz, the SQUID array amplifier can easily possess switching speeds approaching several tens of pico-seconds. Phase II will design, develop, and demonstrate a novel differential input version of the SQUID array amplifier, which will increase its gain by a factor of two while maintaining its high bandwidth. The amplifier chip will be integrated in a cryopackage with a semiconducting-based amplifier to facilitate its instrumentation with room temperature processing electronics. Commercial Applications and Other Benefits as described by the awardee: A low-noise, high-speed, SQUID amplifier chip should find use in many high-speed digital systems, such as analog-to-digital converters (ADCs) and digital receivers. Such a SQUID coupled to a large transformer (100 nH) would make an amplifier with sub-pico ampere sensitivity possible for many applications, including non-invasive medical diagnostic instrumentation or the readout of cryogenic detector arrays.