SPAD Receiver with Adjustable Subareas for LiDAR Aiming Error Compensation
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Solution Overview
Problem
Existing scanning measuring devices face limitations in detecting weak backscattered pulses at large distances due to noise interference and require larger receiver areas, which increase background light and reduce signal-to-noise ratio, especially in airborne LiDAR systems where aiming errors due to finite transit time complicate precise distance measurement.
Innovation Solution
A measuring device with a receiver based on an array of single photon avalanche photodiodes (SPAD) that allows for adjustable active subareas, synchronized with the beam steering element, enabling precise detection of weak signals and compensating for aiming errors by optimizing the receiver area based on the transmission direction, thereby reducing background light and enhancing measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the receiver area is increased to detect weak backscattered pulses at large distances, then the detection capability is improved, but the background light increases and the signal-to-noise ratio decreases
Solution Approach 1:
The receiver area is divided into multiple individually addressable subareas (pixels) on the photodetector array. Only the specific subarea corresponding to the current beam direction is activated for signal acquisition, while other subareas remain inactive. This segmentation allows the effective receiver area to be minimized for each measurement, reducing background light intake while maintaining the capability to detect weak signals from large distances.
Solution Approach 2:
The active subarea of the receiver is dynamically adjusted and synchronized with the beam steering element in real-time. As the beam direction changes during scanning, the active subarea is repositioned to match the new direction. This dynamic adaptation ensures that the receiver always captures signals from the correct direction with minimal background light, resolving the contradiction between detection capability and background light reduction.
2Reliability
If a larger receiver area is used to capture returning radiation, then the signal strength is improved, but the background light interference increases
Solution Approach 1:
Instead of uniformly activating the entire receiver area, the system applies local quality by selectively activating only the specific subarea that corresponds to the current beam direction. This localized activation ensures that the receiver captures the maximum possible signal from the intended direction while minimizing exposure to background light from other directions, thus improving signal strength without proportionally increasing background light interference.
Solution Approach 2:
The system performs preliminary action by pre-calculating and pre-positioning the active subarea before each signal acquisition event. The control unit determines the required active subarea based on the beam steering element's position and activates it in advance, ensuring optimal signal capture while minimizing background light interference from the outset of each measurement cycle.
3Productivity
If the beam steering element operates rapidly to achieve high acquisition rates, then the productivity is improved, but the aiming error due to finite transit time increases
Solution Approach 1:
The system implements feedback by continuously monitoring the position of the beam steering element and using this information to dynamically adjust the active subarea position on the receiver. The control unit receives position information from the beam steering element and synchronizes the active subarea accordingly, compensating for aiming errors caused by rapid steering movements and finite light transit time. This feedback mechanism maintains measurement precision while enabling high acquisition rates.
Solution Approach 2:
The system performs preliminary action by predicting and pre-positioning the active subarea based on the beam steering element's motion trajectory and the expected light return time. By anticipating the beam direction at the moment the reflected light returns, the system compensates for aiming errors before they affect measurement accuracy, allowing rapid beam steering without sacrificing precision.
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
Enables fast and precise distance measurements over extended ranges with improved signal-to-noise ratio and reduced background light, allowing for accurate detection of weak signals and minimizing aiming errors, even at large distances.
Implementation Method 1
a receiver (30) based on an array of single photon avalanche photodiodes (SPAD) that is configured to detect a received signal based on at least a part of the returning transmitted radiation
Implementation Method 2
a beam steering element (38) which is configured to deflect the transmitting radiation and to set a time-varying transmitting direction of the transmitting radiation
Implementation Method 3
a radiation source (26) for generating a transmitting radiation
Data Source
Figure 1a
Figure 1b~1c
Figure 1d
AI summary
The invention relates to a measuring device with scanning functionality for the optical measurement of an environment, wherein the measuring device has a sensor with an arrangement of microcells as a receiving surface and direction-dependent active sub-areas of the receiver are defined depending on the transmission direction of the transmission radiation in order to adjust the active receiver surface to a varying imaging position of the received radiation.