A Compact High Frequency Voltage Amplifier for Superconductor-Semiconductor Logic Interface

TL;DR

This paper presents a compact, on-chip superconductor voltage amplifier designed to boost SFQ circuit signals, offering high frequency, low noise, and programmable gain, improving cryogenic-superconductor interface performance.

Contribution

It introduces a novel integrated superconductor voltage amplifier with high frequency operation, low noise, and programmable gain, compatible with SFQ circuits, and demonstrates its effectiveness through fabrication and testing.

Findings

Achieved about 10 dB gain with 600 uV output at ~25 GHz

Circuit size is 160 um x 320 um

Simulations show over 20 dB gain with more levels

Abstract

The many advantages of cryogenically-cooled Single-Flux Quantum (SFQ) circuits imply that the high speed and low voltage output signals must be amplified and interfaced with standard electronics. State-of-the-art low-noise and wide-band amplifiers are required to interface with room temperature electronics. One solution is to place preamplifiers at the cryogenic stage, which requires specific semiconductor design and fabrication. However, a more viable and energy-efficient approach is to integrate the pulsed logic circuit output stages with on-chip superconductor preamplifiers. We designed, fabricated, and tested an on-chip compact voltage multiplier integrated with the output stage of SFQ circuits to increase the voltage amplitude of SFQ pulses. The circuit is designed with the same technology as the logic circuit hence its noise level is lower, and it works at higher frequencies compared to CMOS amplifiers and due to quantized nature of it there is no added noise. The fabricated circuit has a compact size of 160 um x 320um and provides about 10 dB gain with measured 600 uV output voltage at frequencies up to ~25 GHz in simulations. By stacking more levels, over 20 dB gain at circuit level is achievable as shown in simulations. Moreover the gain of the superconductor voltage amplifier is quantized and programmable.