A 70mW Indirect Time-of-Flight Image Sensor with Depth Dynamic Range Enhancement and Fixed Depth Noise Compensation

Indirect time-of-flight (iTOF) is a 3D depth-sensing technology that provides the distance to the object by measuring the phase difference of emitted and reflected waves of light. Usually, iTOF sensors consume power over 200 mW owing to high frequency modulation, which prevents them from the application to the energy limited wearable devices for VR/AR. To minimize column fixed depth noise (FDN), the TX driver typically has a double-sided clock tree that provides TX signals from both the left and the right sides of the pixel array [1], [2]. However, the double-sided driver consumes significant power even though the column FDN is still present. Moreover, the clock tree generates a huge peak current to induce depth noise. Some sensors employed a clock chain to distribute the peak current [3], [4]. Because the chain induces inherent row FDN, they used a DLL [3] or two opposite-directional chains [4] for the post compensation. However, these schemes still have column FDN, power consumption from the double-sided driver, and PVT variation. Another important issue is a limited depth dynamic range (DDR) because reflected light power falls along with the squared distance. Saturation occurs for short range (SR) whereas noise overwhelms signal for long range (LR). For the WDDR, two or multiple shots of images should be synthesized while consuming additional power.