Time-of-Flight Camera Reference Photosensor Saturation Control
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Solution Overview
Problem
Time-of-flight cameras face challenges in comparing measurement results due to varying integration times, leading to unreliable distance measurements, especially when the reference photosensor reaches saturation.
Innovation Solution
A time-of-flight camera system with both a photosensor and a reference photosensor, both configured as photomixing detectors, share the same integration time to prevent saturation and ensure comparable measurements, with the integration time being dimensioned to maintain the reference photosensor within its optimal working range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the integration time is increased to improve distance measurement accuracy, then the measurement precision is improved, but the reference photosensor reaches saturation
Solution Approach 1:
The system divides the photosensing function into two separate sensors: a photosensor for distance measurement and a reference photosensor for reference signal acquisition. This segmentation allows each sensor to be optimized for its specific function, with the reference photosensor protected from saturation by dedicated signal path isolation.
Solution Approach 2:
A beam splitter is introduced as an intermediary element to separate the incoming light into two paths: one leading to the photosensor and another to the reference photosensor. This intermediary allows the reference photosensor to receive a controlled portion of the light signal without being exposed to the full intensity that would cause saturation.
2Reliability
If different integration times are used for photosensor and reference photosensor, then saturation can be avoided, but measurement reliability decreases
Solution Approach 1:
The system dynamically adjusts the integration time based on the specific measurement conditions and light intensity levels. The control unit monitors the reference signal and automatically optimizes the integration time to maintain measurement reliability while preventing saturation, adapting to changing environmental conditions in real-time.
Solution Approach 2:
The integration time parameter is made variable and is adjusted according to the measured light conditions. By changing this parameter dynamically rather than using a fixed value, the system maintains optimal measurement precision across varying illumination levels while preventing reference photosensor saturation.
3Measurement precision
If the reference photosensor is exposed to high light intensity, then reference signal quality improves, but the sensor reaches saturation
Solution Approach 1:
The beam splitter acts as an intermediary that divides the incident light between the photosensor and reference photosensor. This allows the reference photosensor to receive sufficient light for quality reference signals while the optical division prevents excessive intensity that would cause saturation.
Solution Approach 2:
Different optical path qualities are provided for the two sensors: the photosensor receives the full light signal for distance measurement, while the reference photosensor receives a divided portion optimized for reference signal generation. This local optimization of light distribution prevents saturation while maintaining reference signal quality.
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 ensures reliable distance measurements by maintaining the reference photosensor below saturation, allowing for accurate comparison and dynamic adaptation to light conditions, thereby improving the reliability and accuracy of distance determination.
Implementation Method 1
a semiconductor is configured to receive and convert electromagnetic radiation into an electric measured quantity
Implementation Method 2
systems that measure distances directly from the time of flight (TOF) but also and especially all time-of-flight camera systems or 3D-TOF camera systems that acquire time-of-flight information from the phase shift of emitted and received radiation
Data Source
AI summary
A time-of-flight camera includes a photosensor and a reference photosensor. Each of the photosensors have accumulation gates and each are configured as a photomixing detector (PMD). A readout device is connected to the accumulation gates of the photosensor and to the accumulation gates of the reference photosensor. The readout device is configured to read out an electric quantity that corresponds to a charge that is present at respective ones of the accumulation gates. An integration time of accumulating the charges is the same for the photosensor and for the reference photosensor and is dimensioned so as to prevent the reference photosensor from reaching saturation during operation of the time-of-flight camera.