Characterization of aliased noise in the Advanced ACTPol receiver

Abstract: Advanced ACTPol is the second generation polarization-sensitive upgrade to the $6\, \rm m$ aperture Atacama Cosmology Telescope (ACT), which increased detector count and frequency coverage compared to the previous ACTPol receiver. Advanced ACTPol utilizes a new two-stage time-division multiplexing readout architecture based on superconducting quantum interference devices (SQUIDs) to achieve a multiplexing factor as high as 64 (rows), fielding a 2,012 detector camera at 150/220 GHz and two 90/150 GHz cameras containing 1,716 detectors each. In a time domain system, aliasing introduces noise to the readout. In this work we present a figure of merit to measure this noise contribution and present measurements of the aliased noise fraction of the Advanced ACTPol receiver as deployed.