Optical Sensor Crosstalk Correction via Reference Pulse
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Solution Overview
Problem
Time-of-flight (TOF) sensors face errors in distance measurement due to mixed signals from target objects and cover panels, leading to incorrect distance calculations, and existing methods require high resolution and increased costs or periodic updates for crosstalk value calculation.
Innovation Solution
An optical sensor with a reference pulse generation circuit, a light-emitting element, a cover panel, and a photon-counting first light-receiving element, which uses a determination circuit to differentiate between target object and cover panel reflected light, allowing for accurate distance measurement by updating the crosstalk value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cover panel is added to the TOF sensor, then light transmission and reflection are improved for sensing, but signal mixing occurs between target object reflected light and cover panel reflected light causing measurement errors
Solution Approach 1:
The system performs preliminary measurement in a state where no target object is present to obtain the cover panel reflected light signal characteristics before actual measurement. This preliminary action allows the system to store reference data (cover panel reflected light intensity and timing) that can be used to subtract or filter out the cover panel signal during subsequent measurements, thereby eliminating its interfering effect on distance measurement accuracy
Solution Approach 2:
The invention extracts and separates the cover panel reflected light signal from the mixed signal received during measurement. By using the preliminarily obtained cover panel signal characteristics, the system can identify and remove the cover panel reflection component from the total received signal, leaving only the target object reflected light signal for accurate distance calculation
2Measurement precision
If histogram method is used to separate cover panel and target object reflected light, then correct distance measurement is achieved, but resolution decreases compared to DLL circuit scheme
Solution Approach 1:
The invention introduces an intermediary approach by using the cover panel reflected light signal as a reference mediator. The system uses the preliminarily obtained cover panel signal to mediate the separation of target object signal from the mixed signal, enabling accurate distance measurement without requiring the complex high-resolution histogram method while maintaining better resolution than conventional approaches
3Manufacturing precision
If DLL circuit is used for distance measurement, then high resolution is achieved, but erroneous distance calculation occurs due to mixed signals from cover panel reflection
Solution Approach 1:
The system applies preliminary anti-action by obtaining the cover panel reflected light signal characteristics in advance (when no target object is present) and using this information to counteract or compensate for the cover panel reflection interference during actual measurement. This preliminary counter-measure prevents the mixed signal from causing erroneous distance calculations while preserving the high resolution capability of the DLL circuit
4Measurement precision
If crosstalk value calculation is performed periodically, then accurate distance measurement is maintained, but measurement time and processing overhead increase
Solution Approach 1:
The system performs the crosstalk value calculation (cover panel signal characterization) in advance as a preliminary action, storing the results for reuse during subsequent measurements. This eliminates the need for periodic recalculation during normal operation, significantly reducing measurement time and processing overhead while maintaining accurate distance measurement by using the pre-computed crosstalk value
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 accurate distance measurement to a target object based on time-of-flight by correctly distinguishing between target object and cover panel reflected light, improving measurement resolution and reducing costs associated with high-resolution requirements.
Implementation Method 1
a light-emitting element 3 that emits light toward a target object 19 on the basis of the reference pulse signal TX
Implementation Method 2
a cover panel 4 that transmits a portion of the light emitted from the light-emitting element 3 and reflects the remaining portion
Implementation Method 3
a photon-counting type of first light-receiving element 5 that is provided in such a way as to be able to receive target object reflected light L1 that is reflected by the target object 19 and cover panel reflected light L2 that is reflected by the cover panel 4
Implementation Method 4
A TOF sensor measures the distance between the TOF sensor and a target object by calculating the distance on the basis of the time difference between the time at which light is emitted toward the target object and the time at which reflected light, produced by the emitted light being reflected by the target object, is received
Data Source
AI summary
An optical sensor for appropriately updating a crosstalk value is provided with: a photon-counting type of first light-receiving unit for receiving target object reflected light and cover panel reflected light; and a determination circuit that determines whether or not the target object reflected light is received by the first light-receiving unit, on the basis of a first received light pulse signal that is based on at least one of the target object reflected light and the cover panel reflected light, and a reference pulse signal.