How LiDAR Works: The Time-of-Flight (ToF) Principle

One of the most commonly used techniques in LiDAR technology is Time-of-Flight (ToF). This method measures the time elapsed between the emission of a photon pulse from the LASER and its detection upon returning after reflection from a target.

Given that photons travel at the speed of light, the distance to the object can be calculated by simply multiplying the ToF by the speed of light.

Key Components of a LiDAR System

A LiDAR system comprises three fundamental components:

1. The LASER

2. The Photodetector

3. The Sensor Read-out and Processing Electronics

1. The LASER

The LASER can be either an external component or integrated within the sensor. Critical parameters include:

• Pulse Width: Narrow pulses improve measurement accuracy.

• Power Output: Determines the maximum measurable distance.

• Beam Coverage: Ensures illumination of the entire FOV.

2. The Photodetector

The photodetector is responsible for converting absorbed photons into an electrical signal. It can be a conventional photodiode, but for advanced applications, Move-X utilizes SPADs (Single Photon Avalanche Diodes). These sensors are capable of detecting individual photons, allowing for unparalleled accuracy and extended measurement range.

Other optical components such as lenses, microlenses, and optical filters play a crucial role in optimizing performance by:

• Expanding the active detection area

• Eliminating unwanted background light

• Enhancing the signal-to-noise ratio

3. Sensor Read-out and Processing Electronics

The processing electronics depend significantly on the type of photodetector used. For SPADs, the output is inherently digital and consists of two major elements:

• Time-to-Digital Converter (TDC)

• Histogrammer

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‍Time-to-Digital Converter (TDC)

The TDC measures the ToF and converts it into a digital code. One of the simplest architectures for achieving this involves a delay line, composed of multiple cells with known delays. The number of activated cells between LASER emission and detection gives the ToF measurement.

While this technique offers excellent precision (with delays as small as a few picoseconds per cell), it is limited for long-range measurements due to the excessive number of required delay cells. Alternative techniques include:

• Vernier Cell

• Gated Ring Oscillator (GRO) TDC

• Nutt Interpolation

Regardless of the TDC architecture, the system outputs a digital code representing the measured distance.

Histogrammer: Filtering Background Noise

In real-world environments, LiDAR sensors must contend with background light in addition to LASER photons. Optical filtering and photon coincidence circuits—which use multiple photodetectors in parallel—help mitigate unwanted signals.

However, some residual noise remains, making it difficult to distinguish between LASER and background photons. A histogrammer is employed to address this issue:

• Instead of a single measurement per frame, multiple measurements are recorded.

• The results are stored in a counter, forming a histogram.

• Since background noise is randomly distributed, the highest peak in the histogram corresponds to the correct distance measurement.

Applications of LiDAR Technology

LiDAR technology enables highly accurate, efficient, and precise environmental mapping, even over long distances. Its compact form factor and versatile capabilities make it ideal for various applications, including:

🚗 Automotive: Integral to ADAS (Advanced Driver Assistance Systems) and autonomous driving.

🎮 Consumer Electronics: Enhancing AR/VR experiences with advanced spatial mapping.

🏭 Industrial Automation: Used for precision manufacturing, robotic vision, and automated navigation.

Conclusion

LiDAR technology represents a breakthrough in distance measurement and environmental sensing, unlocking new possibilities across multiple industries. With Move-X's cutting-edge advancements in SPAD-based LiDAR systems, we are pushing the boundaries of accuracy, efficiency, and innovation. 🚀

Stay tuned for the future of LiDAR technology—where precision meets performance!

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