Dual-mode, in-pixel linear and single-photon avalanche diode readout for low-light dynamic range extension in photodetector arrays

This paper presents an approach for combining linear and single-photon avalanche diode operation in a single pixel to enhance low-light dynamic range of a photodetector array. Pulse frequency modulation and avalanche pulse counting provide in-pixel digitization for both operation modes, enabling full parallel measurement across the array. An 8×8 array architecture is fabricated in standard 180 nm CMOS and demonstrates 85 dB optical dynamic range and a maximum low-light frame rate of 130 Hz. This approach represents the first reported photodetector array architecture supporting both linear and single-photon diode operation in each pixel.

I. Introduction

Optical sensing with visible light is used broadly across scientific applications, where its utility as a non-invasive measurement technique is essential for medical, environmental, and life sciences applications. In particular, low-noise imaging and fluorescence measurement rely heavily on high quality solid-state imagers, including cooled CCD sensors or scientific CMOS image sensors (CIS). For low-light, low-magnitude photocurrent sensing with CMOS image sensors, the integration time must be long, yielding low (<5 Hz) frame rates [1], and precise analog circuits are necessary to reduce temporal readout noise and signal-dependent junction leakage current.