Combined In-Pixel Linear and Single-Photon Avalanche Diode Operation With Integrated Biasing for Wide-Dynamic-Range Optical Sensing

This article presents a fully integrated, wide linear dynamic range (DR) optical sensor array combining linear and single-photon avalanche diode (SPAD) operation within each pixel. A pulse-counting readout scheme provides in-pixel digitization in an area-efficient manner for both the operation modes, enabling fully parallel measurement across the array. The proposed dual-mode optical sensor array alternately requires high-voltage (10-20 V) and low-voltage supply (2-5 V) for reverse bias of the photodiodes, which is provided by a reconfigurable, closed-loop high-voltage charge pump in the same substrate. An 8 × 8 array architecture along with the dual-mode bias generator is fabricated in a general purpose 180-nm CMOS process and demonstrates 129-dB DR while maintaining linear photoresponse operating with a dual-mode frame rate of 20 Hz. We present a pixel design methodology for implementing a dual-mode optical sensor scalable to an array format, as well as high-voltage dc-dc conversion in a low-voltage CMOS process.