ToF system, useful for distance measurement and object detection
Can measure distances from less than 10cm to less than 15m
Need for assistance in solution to prevent distortion of measurement results


Distance measurement and object detection play a vital role in a variety of applications, including factory automation, robotics, and logistics. Safety-related applications in particular may require technology to detect and respond to objects or people at a certain distance. For example, a robot arm may need to stop immediately when a worker enters a danger zone.

Time of Flight (ToF) technology is increasingly being used for these purposes. ToF technology uses a modulated light source, such as a laser, to emit light, which then bounces off one or more objects and is captured by a sensor or camera.

Knowing the time difference, ∆t, between when the light is emitted and when the reflected light is received, we can find the distance. This time delay is twice the distance between the camera and the object (round trip). Therefore, the distance can be calculated using the formula d = (c × ∆t) / 2, where c is the speed of light. The ToF camera outputs 2D data along with the required depth information.

ToF captures the entire image at once, scanning line by line, and does not require relative movement between the sensor and the target object. ToF is classified as Light Detection And Ranging (LiDAR), but is strictly a "flash" LiDAR-based technique, not a "scanning" one.

There are basically two methods that can be used to measure the time of flight of an optical pulse using ToF: pulse operation based on CCD (Charge Coupled Device) technology, and CW (Continuous Wave) operation. Pulse mode measures the time elapsed between the time an optical pulse is emitted and received, while CW mode calculates the phase shift between the emitted modulated optical pulse and the received modulated optical pulse. Both methods have their own advantages and disadvantages.

Pulse mode emits light with high energy and short pulses, and is more robust to ambient light, making it more suitable for outdoor applications. On the other hand, CW mode is easier to implement, as the light source does not need to be extremely short, and the rising/falling edges are fast. However, it becomes difficult to implement when high-precision requirements require high-frequency modulation signals.

High chip resolution is possible depending on the existing pixel size, so it can recognize objects and movements as well as measure distances. The measurement distance can be from less than a few centimeters (<10cm) to less than a few meters (<15m). However, not all objects can be detected at the same level. The measurement results can vary depending on the condition, reflectivity, speed, etc. of the object. Measurement results can also be distorted by environmental factors such as fog or strong sunlight.

Analog Devices (ADI) offers comprehensive 3D ToF solutions to support rapid implementation of 3D ToF systems. These solutions integrate data processing, laser drivers, power management, and software/firmware into a single unit. Therefore, only an emitter to emit frequency-modulated optical signals and a detector to detect reflected signals are required as separate additional components. The figure below shows a block diagram of the solution.

Such systems can be easily developed using an analog front end (AFE) with depth calculation capabilities. The ADI 'ADDI9036' is such a product, a comprehensive CCD ToF signal processor that integrates a laser diode driver, a 12-bit ADC, and a high-precision clock generator (for timing the CCD and laser). The ADDI9036 processes raw image data from a VGA CCD sensor to generate depth/pixel data.

ADI also works with design partners to provide integrated modules or development platforms. Users can develop their own specific algorithms using these evaluation systems and use these modules and platforms to reduce development time. This is useful for the development of industrial facilities and electrical equipment where pressure for rapid development is increasing.



This article is a summary of the article titled 'Time of Flight System for Distance Measurement and Object Detection' by Thomas Brand, FAE, Analog Devices (ADI).

References, " 3D Imaging with ADI Time of Flight Technology " ADI, 2020.