SPAD Time-of-Flight Sensing With Dynamic Ambient-Light Thresholding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing SPAD-based distance-measuring sensors struggle with distinguishing desired light events from unwanted interference events, particularly in varying ambient light conditions, leading to unreliable measurements due to the pile-up effect and challenges in setting an effective threshold.
Innovation Solution
An optoelectronic sensor with a control and evaluation unit that dynamically adjusts the threshold based on ambient light levels, using lookup tables to parameterize the threshold with a safety margin, ensuring reliable detection of light transit times by separating useful light signals from interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a static threshold is used to separate useful light events from interference events, then the device complexity is reduced, but the measurement precision deteriorates under varying ambient light conditions
Solution Approach 1:
The patent implements dynamic threshold adjustment by continuously adapting the threshold value based on the currently detected ambient light level. The control unit monitors the ambient light situation and automatically modifies the threshold for separating useful light events from interference events, ensuring optimal measurement precision without requiring manual intervention or complex calibration procedures.
Solution Approach 2:
The system employs feedback mechanisms where the detected ambient light level is fed back to the control unit, which then adjusts the threshold accordingly. This closed-loop control ensures that the threshold always adapts to current measurement conditions, maintaining high measurement precision while keeping the device complexity manageable through automated control.
2Measurement precision
If manual threshold adjustment is implemented to adapt to ambient light conditions, then the measurement precision is improved, but the ease of operation deteriorates
Solution Approach 1:
The sensor system performs self-adjustment of the threshold value based on the ambient light conditions it detects. The control unit automatically monitors the ambient light level and modifies the threshold without requiring any manual intervention from the user. This self-service mechanism maintains high measurement precision while preserving ease of operation, as the system adapts autonomously to changing conditions.
3Reliability
If the threshold is set too low to detect weak useful light signals, then the sensitivity is improved, but false detections from interference events increase
Solution Approach 1:
The threshold is dynamically adjusted based on the detected ambient light level. When ambient light conditions change, the threshold automatically adapts to maintain optimal separation between useful light signals and interference events. This dynamic behavior allows the system to detect weak useful light signals while minimizing false detections, as the threshold is continuously optimized to the current measurement situation.
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 reliable distance measurements in varying ambient light conditions, allowing detection of low-reflecting objects at great distances and reducing false detections by minimizing computational effort.
Implementation Method 1
In an avalanche photodiode (APD), the incident light triggers a controlled avalanche effect. This multiplies the charge carriers generated by incoming photons, creating a photocurrent that is proportional to the light reception intensity
Implementation Method 2
a light transmitter (12) emits a light signal (14), which is received in a light receiver (22) after diffuse remission or direct reflection from an object whose distance is to be measured
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An optoelectronic sensor (10) for measuring the distance of an object (18) in a detection area (16) using a time-of-flight method is specified, wherein the sensor (10) comprises a light transmitter (12) for emitting a light signal (14) into the detection area (16), a light receiver (22) with a first plurality of avalanche photodiodes (24) in Geiger mode for detecting received light (20) from the detection area (16), a second plurality of time-of-flight measuring units (28) for determining individual light travel times between the emission of a light signal (14) and the triggering of a detection event in an avalanche photodiode (24), and a control and evaluation unit (32) which is designed to collect individual light travel times in a histogram, to localize a useful light signal (44) in the histogram using a threshold (38), and to determine a distance value to the object from the useful light signal (44). (18) to be determined.First, an extraneous light level is estimated from the histogram and then, based on the extraneous light level, the threshold (38) is set so that it lies with a safety margin above an expected exponentially decreasing number of noise and extraneous light events.