  The Skipper CCD-in-CMOS Parallel Read-Out Circuit V2 (SPROCKET2) is designed
to enable high frame rate readout of Skipper CCD-in-CMOS image sensors. The
SPROCKET2 pixel is fabricated in a 65 nm CMOS process and occupies a 60$\mu$m
$\times$ 60$\mu$m footprint. SPROCKET2 is intended to be heterogeneously
integrated with a pixelated Skipper CCD-in-CMOS sensor, such that one readout
pixel is connected to a multiplexed array of 16 active image sensor pixels, to
match their spatial geometry. Our design benefits from the Skipper CCD-in-CMOS
sensor's non-destructive readout capability to achieve exceptionally low noise
through multi-sampling and averaging while optimizing for total power
consumption. The pixel readout utilizes correlated double sampling to minimize
1/f noise and includes "pile-up" of ten successive samples in the analog domain
before digitizing at a rate of 66.7 ksps. Measurement results of in-pixel
serial SAR ADC show DNL and INL of ~0. 44 LSB and 0.58 LBS respectively. A
large area array of 20,000 SPROCKET2 ADC pixels (multiplexed 1:16 to 320,000
sensor pixels) is currently under test. By reading out data over a 10 Gbps
optical link, this pixel design enables a frame rate of $\sim$ 4 kfps for large
sensing areas with minimal sensing deadtime. In the highest gain mode, the
pixelated ADC has an input-referred resolution of 10$\mu$V with a simulated
power consumption of 50$\mu$W. The pixel operates with constant current draw to
minimize power-rail crosstalk.
