Lidar Receiver Ambient Light Compensation Threshold Adjustment
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Solution Overview
Problem
Lidar and optical rangefinder systems face challenges in effectively rejecting spurious inputs from detector noise and ambient light, which can vary with environmental conditions, leading to inaccurate distance measurements and increased noise levels.
Innovation Solution
The system employs a combination of methods to adjust the threshold level based on DC-coupled signal measurements and timer count values during periods without light-pulse detection, using filtering and nonlinear amplification to differentiate between noise and signal components, and classifying timer count values to calibrate and adjust the threshold for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed threshold is used to differentiate signal pulses from noise, then the system structure remains simple, but the reliability of signal detection deteriorates under varying ambient light conditions
Solution Approach 1:
The system performs preliminary measurement of the ambient light level before signal detection. The ambient-light compensator measures the DC-coupled signal during intervals when no light pulses are present, establishing a baseline noise level. This preliminary action enables the threshold to be set appropriately for current conditions, improving detection reliability without requiring complex real-time adjustment mechanisms during active measurement.
Solution Approach 2:
The system implements feedback by continuously monitoring the DC-coupled signal level and using this information to adjust the threshold dynamically. The measured ambient light level feeds back to the threshold setting mechanism, allowing the system to adapt to changing environmental conditions. This feedback loop maintains high detection reliability while keeping the overall system structure relatively simple by using the existing detector output rather than adding separate sensing elements.
2Measurement precision
If the threshold is lowered to detect small signal pulses, then sensitivity improves, but false triggers from noise increase
Solution Approach 1:
The system changes the threshold parameter dynamically based on measured ambient light conditions rather than using a fixed value. By adjusting the threshold as a variable parameter that adapts to environmental conditions, the system maintains high sensitivity for detecting small signal pulses while compensating for increased noise levels. The threshold is set proportional to the measured DC signal level, ensuring appropriate discrimination between signal and noise across varying conditions.
3Measurement precision
If ambient light measurement is performed continuously, then noise compensation accuracy improves, but the response time for distance measurement decreases
Solution Approach 1:
The system performs ambient light measurement periodically during intervals when no light pulses are being detected or transmitted. Rather than continuous measurement, the ambient-light compensator samples the DC-coupled signal at discrete times when the detector is not expecting signal pulses. This periodic approach provides adequate noise compensation accuracy while preserving response time for distance measurements, as the measurements occur during natural idle periods in the measurement cycle.
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 significantly improves signal detection by reducing false triggers and maintaining sensitivity to small signal pulses, even in the presence of varying ambient light and noise sources, thereby enhancing the accuracy and reliability of distance measurements.
Implementation Method 1
an optical detector that converts light to an electrical signal
Data Source
AI summary
A lidar and optical rangefinder receiver improves signal detection in the presence of varying levels of environmental light and other noise sources. The occurrence of false triggers, due to noise, during periods when no optical pulse is emitted is used to adjust the pulse detection threshold level and simultaneously calibrate the time-of-flight timer. The photodetector's response to ambient light is also used to adjust the threshold level. Example systems include signal detection electronics with dynamic thresholding and real-time calibration of timing electronics, in which the threshold level for signal detection is adjusted in response to both information acquired during calibration cycles and ambient light measured between active rangefinding cycles.