SPAD ToF Sensor Asymmetric Signal Path Calibration
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Solution Overview
Problem
The physical layout of single photon avalanche diode (SPAD) Time of Flight sensors is complex and often results in non-optimal arrangements that lead to significant deterioration in device cost and quality due to constraints such as equal signal path lengths between reference and return arrays, causing underutilization of available area and routing channel issues.
Innovation Solution
Implementing an asymmetrical signal path configuration by minimizing the path distance between the return array and readout circuitry and providing a calibration signal path that matches the reference array signal path, allowing for calibration of signal path differences to minimize timing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If equal signal path lengths are enforced between reference and return arrays, then timing differences are minimized, but area utilization deteriorates and routing complexity increases
Solution Approach 1:
The patent applies asymmetry by allowing different signal path lengths for reference and return arrays. Instead of enforcing equal path lengths, the system uses independent routing for each array, accepting asymmetric path lengths to achieve better area utilization and simpler routing while compensating for timing differences through calibration
2Measurement precision
If equal signal path lengths are enforced between reference and return arrays, then timing differences are minimized, but routing complexity increases
Solution Approach 1:
The system accepts asymmetric routing configurations where reference and return arrays have different path lengths and routing complexities. This approach simplifies the overall routing design by eliminating the constraint of equal path lengths, allowing each array to be routed independently to optimal locations
3Area of stationary object
If asymmetrical signal path configuration is implemented, then area utilization improves, but timing differences increase
Solution Approach 1:
The system performs preliminary calibration to measure and compensate for timing differences caused by asymmetric signal paths. By characterizing the timing offsets during calibration and applying compensation algorithms, the system achieves both good area utilization and acceptable measurement precision
Solution Approach 2:
The system uses feedback through calibration measurements to determine actual signal path timing differences. This feedback information is then used to adjust and compensate for timing offsets, allowing the system to maintain measurement precision despite asymmetric routing configurations
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 configuration enables better utilization of available area, reduces routing resources, and compensates for signal path mismatches, improving the overall performance and efficiency of the SPAD sensor module.
Implementation Method 1
Single photon avalanche diode (SPAD) Time of Flight (ToF) sensors typically comprise arrays of single photon avalanche diodes
Implementation Method 2
an illumination source in the form of a vertical cavity surface emitting laser (VCSEL)
Implementation Method 3
Single photon avalanche diode (SPAD) Time of Flight (ToF) sensors typically comprise arrays of single photon avalanche diodes
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A single photon avalanche diode based range detecting apparatus comprising: a reference array of single photon avalanche diodes configured to receive light from a illumination source via an internally coupled path; a return array of single photon avalanche diodes configured to receive light from the illumination source via an external free space path; a calibration pulse generator configured to generate a calibration signal pulse; and readout circuitry configured to receive: an output of the reference array via a reference signal path; an output of the return array via a return signal path; and an output of the calibration pulse generator via a calibration signal path, the calibration signal path comprising a first signal path substantially following the reference signal path, wherein the readout circuitry is configured to determine a delay difference value between the reference signal path and the return signal path based on the output of the calibration pulse generator via the calibration signal path.