A 1k-pixel CTIA readout multiplexer for far-IR photodetector arrays

SB349 is the first 32 × 32 CTIA readout multiplexer specifically designed for far-IR photodetectors and is operable at cryogenic temperatures at least as low as 1.7 K. Four of these readouts can be butted together to form a 64 × 64 mosaic array. The array is multiplexed into eight parallel outputs and features eight selectable gain settings to accommodate various background levels, auto-zero for better input uniformity, and sample-and-hold circuitry. A special, 2-micron cryo-CMOS process was adopted to prevent freeze out and ensure low noise and proper operation at deep cryogenic temperatures. The read noise of the bare device at 4.2 K and under nominal sampling conditions was measured to be about 250e− for the 106fF signal capacitor with the well capacity of 400ke−. Hybridized to a typical germanium detector, the array should achieve NEP levels in the low 10–18 W/√Hz. An overview of the design and the latest results of the test and characterization of this device are reported in this paper.