2D and 3D integrated image sensor with a bus-sharing mechanism

Abstract

This work develops a 2D/3D integrated image sensor that includes photodiodes, pixel circuits, correlated double sampling circuits, sense amplifiers, a multi-channel Time-to-Digital Converter (TDC), a column decoder, a row decoder, a controller and readout circuits. The photodiode of P-diffusion_N-well_P-substrate is used to sense photos at 2D and 3D modes under different biased voltages. At 2D and 3D modes, a charge supply mechanism and a feedback pull-down mechanism in a pixel circuit are adopted to delay the saturation and accelerate the response, respectively. As well as a multi-channel TDC, rapid parallel reading at a 3D mode is accomplished by using a bus-sharing mechanism. Based on the TSMC 0.35μm 2P4M CMOS technology, a 352×288-pixel 2D and 88×72-pixel 3D integrated image sensor was implemented to have a die size of 12mm×12mm. The dynamic range at a 2D mode can reach 110dB and the depth resolution can be around 4cm at a 3D mode. Therefore, the proposed integrated image sensor can effectively switch between 2D and 3D sensing operations for various multimedia capturing applications.