Lidar Detection Using Encoded Pulses and SPAD Arrays
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Solution Overview
Problem
Current lidar systems face challenges with high power consumption, reliability, and cost due to the need for high peak power laser pulses to detect low reflectivity objects at long distances, which also pose eye safety concerns and limit the density and efficiency of photodetector arrays.
Innovation Solution
The system employs a digital encoded pseudo-random sequence of pulses and uses a high-density array of Single Photon Avalanche Detectors (SPADs) to reduce peak power requirements, enabling low-cost, low-power detection and ranging with improved reliability and accuracy, while using SPADs to enhance weak signal detection and reduce false echo discrimination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high peak power laser pulses are used to detect low reflectivity objects at long distances, then detection capability is improved, but power consumption and eye safety risks worsen
Solution Approach 1:
The patent uses periodic pulsed laser emission instead of continuous wave, with pulse width of a few nanoseconds and repetition time of a few tenths of microseconds. This periodic action allows high peak power only during brief pulses while maintaining acceptable average power consumption, resolving the contradiction between detection capability and power consumption.
Solution Approach 2:
The patent segments the detection process into discrete time slots corresponding to each laser pulse emission and its echo reception. By processing multiple pulses and integrating signals over time, the system achieves improved detection capability for low reflectivity objects without requiring continuously high power, thus reducing overall power consumption.
2Measurement precision
If high peak power laser pulses are used to detect low reflectivity objects at long distances, then detection capability is improved, but eye safety risks worsen
Solution Approach 1:
By using periodic pulsed emission with very short pulse width (a few nanoseconds) and appropriate repetition time, the system delivers high energy in brief intervals while keeping average power low. This temporal segmentation reduces cumulative exposure to the eye while maintaining detection capability through signal integration over multiple pulses.
Solution Approach 2:
The patent applies partial action by using high peak power only during the brief pulse duration necessary for detection, rather than maintaining high power continuously. The excessive peak power is tolerated only for the minimal time required to obtain sufficient signal, thereby achieving detection capability while limiting eye safety risks through restricted exposure time.
3Device complexity
If APD arrays are used with limited spatial size, then device complexity is reduced, but detection precision and density worsen
Solution Approach 1:
The patent merges multiple detection functions into a single integrated photodetector array that processes both spatial and temporal information. By combining the photodetector array with time-correlated single-photon counting electronics and signal integration circuits, the system achieves high detection precision without proportionally increasing device complexity, as the additional functionality is integrated into the existing array architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for long-range detection with lower transmission power, simpler sensor elements, and reduced power consumption, achieving reliable and accurate distance and speed measurements with improved cost-effectiveness and reduced eye safety risks.
Implementation Method 1
The emitted laser pulses are concentrated in a small light spot, that hits the target placed at a distance D, and is scattered back to a receiver
Implementation Method 2
Measuring the delay τD between the emitted pulse and the received echo makes it possible to calculate the distance between, e.g., a car and a target object
Implementation Method 3
an array of photodetectors (e.g., Avalanche Photo Detectors—APDs) and linear TIAs (TransImpedance Amplifiers)
Implementation Method 4
a SPAD sensor operating, e.g., in the Geiger mode, with the echo possibly validated (only) if coherent with the transmitted signal
Data Source
AI summary
A system for detecting objects, for driver assistance equipment in motor vehicles for example, includes a transmitter for transmitting towards an object an optical signal having a signal energy. The optical signal transmitted includes at least one encoded pulse sequence with the signal energy distributed over the pulse sequence. A receiver receives an echo signal resulting from reflection of the optical signal at the object with the time delay of the echo signal is indicative of the distance to the object.