Global shutter‐mesh architecture with surround‐boosted driving scheme for time‐of‐flight depth sensors

Abstract

Presented is an architecture with mesh-structured electronic shutters and surround shutter drivers with positive/negative boosting to enhance the depth accuracy in three-dimensional (3D) depth sensors with a time-of-flight (TOF) measurement scheme. High-frequency modulation in the TOF scheme degrades the charge-transfer efficiency in high-resolution sensors because of the large parasitic resistance and the capacitance of the electronic shutters and shutter lines. This degradation suppresses modulation contrast, which induces depth errors. The global shutter-mesh architecture and surround-boosted driving scheme is implemented for high-modulation contrast in large-format depth sensors with a 1280 × 960 resolution.

Optically triggered global shutter image sensor using single‐photon avalanche diodes

“…The pixel signalling becomes crucial with increasing the image sensor output frame rate [11]. This is due to the operating frequency increase of global shutter (in burst and continuous imaging modes) and readout circuits (rather in continuous imaging mode) to several kHz for continuous imaging mode [12], and to several GHz for burst imaging mode [13].…”

“…Nowadays, millions of pixels are integrated in complementary metal oxide semiconductor (CMOS) image sensors and the shutter signal should drive them simultaneously. Not only the shutter signal must drive the large capacitance of pixel shutter input, but also the resistances of wires that connect the pixels to the shutter driver making the signalling more difficult [11]. It should also be noted that insertion of the repeaters in the shutter driver for the pixel path is difficult due to decrease of the pixel fill factor (the ratio of photosensitive to whole pixel area), array discipline symmetrical design, and crosstalk vulnerability.…”

“…There are three shutter engineering strategies to drive all pixel shutters simultaneously: vertical overflow drain (VOD) [14], shutter‐mesh [11], and 3D‐stacked integration [15]. In the VOD mechanism, by applying a voltage pulse to an image sensor substrate all transfer gates are triggered and shuttering occurs.…”

“…In the VOD mechanism, by applying a voltage pulse to an image sensor substrate all transfer gates are triggered and shuttering occurs. In contrast, shutter mesh uses a mesh of vertical and horizontal metal lines with surrounding drivers from four sides of a pixel array, which is implemented in a hybrid 3D/2D CMOS image sensor in [11]. Moreover, to overcome the RC delay of wires, the 3D‐stacked integration is used in [13] as a CMOS‐CCD hybrid approach.…”