Characterization of Aliased Noise in the Advanced ACTPol Receiver

Advanced ACTPol is the second-generation polarization-sensitive upgrade to the $$6\, {\mathrm{m}}$$ 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 to achieve a multiplexing factor as high as 64 (rows), fielding a 2012 detector camera at 150/220 GHz and two 90/150 GHz cameras containing 1716 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.