A 1-GS/s 6–8-b Cryo-CMOS SAR ADC for Quantum Computing
G. Kiene (QCD/Sebastiano Lab)
R. W.J. Overwater (QCD/Sebastiano Lab)
Alessandro Catania (University of Pisa)
Aishwarya Gunaputi Gunaputi Sreenivasulu (QCD/Sebastiano Lab, NXP Semiconductors)
Paolo Bruschi (University of Pisa)
Edoardo Charbon (QCD/Sebastiano Lab, EPFL Switzerland)
Masoud Babaie (TU Delft - Electronics)
F. Sebastiano (TU Delft - Quantum Circuit Architectures and Technology)
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Abstract
This article presents a two-times interleaved, loop-unrolled SAR analog-to-digital converter (ADC) operational from 300 down to 4.2 K. The 6-8-bit resolution and the sampling speed up to 1 GS/s are targeted at digitizing the multi-channel frequency-multiplexed input in a spin-qubit reflectometry readout for quantum computing. To optimize the circuit for the altered device behavior at cryogenic temperatures, a modified common-mode switching scheme is adopted as well as a flexible calibration. The design is implemented in 40-nm CMOS technology and achieves 36.2-dB signal to noise and distortion ratio (SNDR) for Nyquist input at 4.2 K while maintaining a Walden figure of merit (FOM textsubscript W) of 200 pJ/conv-step (for a 10.8-mW power consumption), including the clock receiver, and 15 pJ/conv-step (for a 0.8-mW power consumption) for just the core ADC. With these specifications, the ADC can support the simultaneous readout of 20 qubit channels with a power consumption of 0.5 mW/qubit, thus advancing toward the full integration of the cryogenic readout for future large-scale quantum processors.