A Cryogenic Readout IC with 100 KSPS in-Pixel ADC for Skipper CCD-in-CMOS Sensors

The Skipper CCD-in-CMOS Parallel Read-Out Circuit (SPROCKET) is a mixed-signal front-end design for the readout of Skipper CCD-in-CMOS image sensors. SPROCKET is fabricated in a 65 nm CMOS process and each pixel occupies a
$50\ \mu \mathrm{m}\times 50\ \mu \mathrm{m}$
footprint. SPROCKET is intended to be heterogeneously integrated with a Skipper-in-CMOS sensor array, such that one readout pixel is connected to a multiplexed array of nine Skipper-in-CMOS pixels to enable massively parallel readout. The front-end includes a variable gain preamplifier, a correlated double sampling circuit, and a 10-bit serial successive approximation register (SAR) ADC. The circuit achieves a sample rate of 100 ksps with
$0.48\ \mathrm{e}_{\text{rms}}^{-}$
equivalent noise at the input to the ADC. SPROCKET achieves a maximum dynamic range of
$9,000\ e^{-}$
at the lowest gain setting (or
$900\ e^{-}$
at the lowest noise setting). The circuit operates at 100 Kelvin with a power consumption of
$40\ \mu W$
per pixel. A SPROCKET test chip was submitted in September 2022, and test results will be presented at the conference.