High Dynamic Range Imaging at the Quantum Limit with SPAD-based Image Sensors

This paper examines methods to best exploit the High Dynamic Range (HDR) of the SPAD in a high fill-factor HDR photon counting pixel that is scalable to megapixel arrays. The proposed method combines multi-exposure HDR with temporal oversampling in-pixel. We present a silicon demonstration IC with 96x40 array of 8.25µm pitch 66% fill-factor SPAD-based pixels achieving >100dB dynamic range with 3 back-to-back exposures (short, mid, long). Each pixel sums 15 bit-planes or binary field images internally to constitute one frame providing 3.75x data compression, hence the 1k frames per second (FPS) output off-chip represents 45,000 individual field images per second on chip. Two future projections of this work are described: scaling SPAD-based image sensors to HDR 1MPixel formats and shrinking the pixel pitch to 1-3µm.