Cryogenic analog-to-digital converters using spread spectrum technology for coherent receivers

Abstract

We propose analog-to-digital converters (ADCs) using spread spectrum technology in cryogenic receivers or at warm room temperature for coherent receiver backend systems. As receiver signals are processed and stored digitally, ADCs play a critical role in backend read-out systems. To minimize signal distortion, the down-converted signals should be digitized without further transportation. However, digitizing the signals in or near receivers may cause radio frequency interference. We suggest that spread spectrum technology can reduce the interference significantly. Moreover, cryogenic ADCs at regulated temperature in receiver dewars may also increase the bandwidth usage and simplify the backend digital signal process with fewer temperature-dependant components. While industrial semiconductor technology continuously reduces transistor power consumption, low power high speed cryogenic ADCs may become a better solution for coherent receivers. To examine the performance of cooled ADCs, first, we design 4 bit 65 nm and 40 nm CMOS ADCs specifically at 10 K temperature, which commonly is the second stage temperature in dewars. While the development of 65 nm and 40 nm CMOS ADCs are still on-going, we estimate the ENOB is 2.4 at 10 GSPS, corresponding to the correlation efficiency, 0.87. The power consumption is less than 20 mW.