A 1∼10MHz Cryo-CMOS Analog Baseband Circuit Achieving 50dB Peak Gain for Superconducting Qubit Readout

This paper designs a cryogenic CMOS analog baseband (ABB) circuit with a $1 \sim 10 \mathrm{MHz}$ bandwidth and a peak gain of 50 dB, suitable for superconducting qubit readout. It also provides guidance for the design of cryogenic building block circuits. The circuit comprises a three-stage transconductance-transresistance programmable gain amplifier (PGA) and a third-order Gm-C low-pass filter (LPF). In the absence of comprehensive cryogenic circuit design models, self-biased circuits and pseudo-differential $\mathbf{G m}$ units are designed to address the issue of limited voltage headroom caused by increased threshold voltages at cryogenic temperatures (CT). The proposed ABB is fabricated in 28 nm bulk CMOS technology and achieves a gain range from 0 to 50 dB with 2 dB steps, and a bandwidth of $1 \sim 10 \mathrm{MHz}$. The power consumption is $0.43 \mathrm{~mW} / \mathrm{MHz}$ at cryogenic temperatures. Keywords-cryogenic, analog base-band circuit