An attenuated-sampling SAR ADC for in-situ signal monitoring in cryogenic silicon spin qubit systems

Abstract Accurate in situ monitoring of qubit control signals in cryogenic environments is expected to help achieve practical-fidelity qubit operations in quantum computers. This paper proposes a cryogenic analog-to-digital converter (ADC) with an energy-efficient attenuated sampling technique for cryogenic in situ signal monitoring. By using this technique, the acquisition of IO-level qubit control signals is enabled using an ADC composed solely of core transistors. This approach allows precise monitoring of qubit control signals inside a refrigerator with no constant current path, thereby making the operation feasible within a limited power budget. Fabricated in 28 nm CMOS, the prototype ADC achieves 11 bit resolution and successfully attenuates input signals from a 2.5 V range to a 0.9 V range, with a power consumption of 23 μW and a sampling frequency of 50 kHz at an operating temperature of 4 K.