What is a ToF sensor?

ToF sensors measure the time it takes for light to travel a distance in a medium. Typically, this is a measurement of the time it takes for the pulsed emitted light to reach the object and reflect back to the ToF sensor. ToF cameras use the ToF measurement principle (ToF image sensor) to determine the distance between the camera and the object or the surrounding environment, and generate a depth image or 3D image from the measured points.
Applications for ToF cameras include laser-based non-scanning lidar imaging systems, motion sensing and tracking, object detection for machine vision and autonomous driving, and terrain mapping.
But how to achieve depth measurement in the above application areas?Below, three methods for determining distance by measuring flight time are described.

The first method is represented at the top of the figure above, emitting pulses of light and measuring the time interval between their reflections and their return.
The second method, shown in the middle of the figure above, modulates the amplitude of the light source and records the phase shift of the reflected light wave.
A third method is represented at the bottom of the image above, firing a square wave with a 50% duty cycle and recording the amount of returned light that arrives within a specific interval.

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