In-pixel A/D converters with 120-dB dynamic range using event-driven correlated double sampling for stacked SOI image sensors

We report in-pixel analog-to-digital converters (ADCs) using event-driven correlated double sampling (CDS) for stacked silicon-on-insulator (SOI) image sensors. The pulse-frequency-modulation ADCs enable a pixel-parallel operation that leads to superior imaging performance. We designed a novel CDS for an ADC comprising comparators, capacitors, and timing control logic circuits to generate clocks for in-pixel operation to suppress reset noise. The developed ADC is successfully confirmed to exhibit an excellent linearity in a wide dynamic range of 120 dB and it shows noise reduction effects, indicating the feasibility of high-performance pixel-level imaging for next-generation image sensors.