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TOF (time of flight)

The ESPROS chips are based on the 3D Time-of-Flight (ToF) principle of light. These chips were designed to enable simple and cost effective 3D ToF cameras. Together with a microprocessor and a few external components a fully functional ToF camera can be built. The measurement functionality supports distance and ambient light measurement with variable integration time and on-chip temperature measurement for drift compensation.

The latest news to: TOF (time of flight)

Cliff detection with 3D time-of-flight imager from ESPROS
Today's best robot vacuums are full of high-tech features. Connected to WiFi they can be controlled by smartphone and even via a voice assistant. The combination of many sensors and software allows to drive around obstacles, map the rooms and plan the most economic cleaning path...
Distance measurement made easy with TOF range 611
With the TOF>range 611 of the Swiss photonic specialist Espros distances up to 15m can be measured...
Miniature ToF imager TOF frame 611 with improved performance
For the 8x8 pixel miniature time-of-flight imager module TOF>frame 611 of the Swiss photonics specialist Espros the range could be increased from 2m to 3m by improved calibration and compensation algorithms. The module has...
TOF CAM 635 - Easy and cost-effective introduction to TOF technology
The time-of-flight technology is gaining more and more importance in the field of 3D imaging. However, the development of a ToF camera requires extensive know-how regarding optics, illumination and signal processing. With the new TOF>cam 635 from the Swiss photonics specialist ESPROS Photonics Corporation, these time-consuming and cost-intensive hardware engineering tasks have already been solved and a cost-effective and powerful 3D time-of-flight camera module is available to the user...
Time-of-Flight (ToF) Imager epc611
At the end of 2017, ESPROS Photonics AG introduced the new Time-of-Flight (ToF) Imager epc611. It has an 8x8 pixel CCD photodiode array and is available as usual in a chip-scale BGA package. The pixel size is 20um x 20um, resulting in an active area of ​​160um x 160um...

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Time-of-Flight (ToF) technology

Time-of-Flight (ToF) is a technology that originated in the 1980s. It is based on the pulse transit time measurement of the light. Light is emitted by a transmitter and reflected by one or more objects. The reflected light beams are detected by a receiver and then the distance is determined.

Single or multiple pulse operation

There are basically two types of transit time measurement: single and multiple pulse operation. In single-pulse operation, the time between the emitted and the received individual light pulse is determined. Due to the constancy of the speed of light (about 300 000 km / s), the elapsed time is proportional to the distance. The situation is different in multi-pulse mode: Here, the phase shift between emitted and received modulated light pulses is determined. This also corresponds to a time and is therefore also proportional to the distance.

ToF pixel sizes

The structure of a ToF pixel in silicon is significantly more complex than the structure of a pixel of a camera chip. For the special chip technology of ESPROS Photonics AG, ToF pixel sizes of 20 x 20 μm were realized. This results in chip resolutions of up to 320 x 240 pixels (QVGA). With this resolution not only distances can be measured, but also objects or gestures can be detected. This complex implementation tasks can be implemented, such. Device control via gestures, monitoring and intelligent control of elevators and escalators, controls of safety areas around robots and cost-effective implementation of automated guided vehicles. The ToF chips from ESPROS Photonics AG are designed as CSP / BGA (Chip Scale Package / Ball Grid Array) and have a thickness of only approx. 50 μm. This allows much smaller and more compact sensor systems to be developed than was possible in the early days of ToF technology.

Principle of distance measurement

In a ToF system, optics, hardware and software design must work together in an appropriate way. First, the maximum distance to the measurement object must be defined. Multi-pulse operation provides a complete 360 ​​° phase for maximum, one-way distance. An example: The 360 ​​° correspond to a maximum distance of 15 m, which means a defined modulation frequency (1 / tMOD). The ToF chip provides 4 samples, so-called DCSx, which are each advanced by 90 ° phases. From these samples, both the amplitude (signal quality) and the distance can be calculated. The output of the 4 DCSx values ​​is done for each of the pixels. Distances can be determined unambiguously up to 15 m. However, if the object is at a distance of 16 m, the ToF system can not unambiguously determine the distance and indicates a distance of 1 m = 16 m - 15 m.


Another aspect is the field of view (FOV) of the ToF camera system. In general, the sensitivity of the ToF chip is not the critical size, but rather the amount of emitted light. The transmitter module must provide sufficient light for reflection in the receiver. The following applies: The greater the distance and the field of view, the greater the amount of light that is necessary for the detection of the object. Since it is an optically measuring system, the laser class must also be taken into account when persons can enter the field of view of the camera system.

Influencing variables of the test object

Naturally, the quality, reflectance and speed of the object also influence the measurement result. There are strong and weakly reflective materials. If the light from the object is reflected too weak, this can be difficult or impossible to detect. This must be taken into account in the design phase through appropriately selected integration times. A high speed of movement of the object requires a sufficiently high computing power or the choice of a suitable controller, which processes the measured values ​​sufficiently fast and delivers meaningful results. Recordings of slow or static objects are much easier to process.


For example, if ToF systems are used inside a building, environmental factors need not be considered. In outdoor use, however, appropriate measures must be taken in hardware and software. Strong sunlight can be suppressed by integrated "Ambient Light Suppression" at the chip level. On the other hand, the measured values ​​for temperature changes must be corrected by means of suitable software routines, depending on the accuracy requirements. Often it is sufficient to work with a higher integration of measured values ​​and to use corresponding correction factors for temperature compensation.

Videos about ToF

Time-of-flight application areas

Automotive Automotive
Transportation Transportation
People counting People counting
Object recognition Object recognition
Control Control
Security Security
Automation Automation
Medicine Medicine
Household Household
Measuring technology Measuring technology
Many more Many more