Time-of-flight circuitry photon count comparison for power reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Direct time-of-flight (dToF) systems face challenges in high-resolution and high-ambient light environments due to data congestion and power dissipation issues, particularly with single photon avalanche diodes (SPADs) triggering on thermally generated minority carriers and ambient light, which affects accurate distance measurement and increases power consumption.
Innovation Solution
The implementation of time-of-flight circuitry that determines a test number of photons at a test point of time and a reference number of photons at a reference point of time within measurement intervals, comparing these to calculate the roundtrip delay of emitted photons, while adapting a confidence value based on the comparison to optimize measurement cycles and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SPADs are used for direct time-of-flight measurement, then distance measurement capability is improved, but power dissipation increases due to triggering on thermally generated minority carriers and ambient light
Solution Approach 1:
The measurement process is segmented into multiple discrete measurement time intervals, with each interval containing a test point of time and a reference point of time. This segmentation allows the system to divide the continuous measurement task into manageable chunks, processing photons in discrete bins rather than continuously, thereby reducing overall power consumption while maintaining measurement accuracy.
Solution Approach 2:
The system employs periodic measurement cycles that repeat the determination of test and reference photon numbers across multiple measurement time intervals. This periodic action allows the system to systematically scan through different time points, comparing photon counts to identify the roundtrip delay, while the repetitive nature enables optimization of power usage by stopping measurement when confidence thresholds are met.
2Measurement precision
If multiple measurement time intervals are processed, then measurement accuracy is improved, but data congestion increases
Solution Approach 1:
The invention extracts and processes only the essential information from each measurement time interval - specifically the photon numbers at the test point of time and reference point of time. By taking out only these critical counts and comparing them directly, the system avoids the data congestion that would result from processing complete photon arrival histories, while still achieving accurate roundtrip delay determination through the comparison results.
Solution Approach 2:
The system creates a simplified representation of the measurement data by copying only the necessary photon count information from each time interval into a comparison structure. This copying approach reduces the data volume significantly compared to storing complete photon arrival records, while preserving the essential comparison needed to determine roundtrip delay through the test versus reference photon number comparison.
3Measurement precision
If measurement cycles are continuously increased, then distance measurement accuracy is improved, but power consumption increases
Solution Approach 1:
The system incorporates feedback through confidence values that are updated based on the comparison of test and reference photon numbers across measurement time intervals. When the confidence value indicates sufficient accuracy has been achieved, the system can terminate or reduce measurement cycles, thereby avoiding unnecessary power consumption. This feedback mechanism dynamically adjusts the measurement process to achieve the minimum required accuracy without excessive power usage.
Solution Approach 2:
The measurement process is made dynamic by allowing the number of measurement cycles to be adjusted based on real-time confidence assessment. Rather than running a fixed number of cycles, the system adapts the measurement duration based on whether the current confidence level is sufficient, enabling the system to use fewer cycles when high accuracy is already achieved and more cycles only when necessary, thus optimizing the power consumption-performance tradeoff.
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 enables efficient and accurate distance measurement with a significant reduction in SPAD power dissipation, achieving a twenty to hundred-fold decrease in power usage and improving the system's ability to operate under high ambient light conditions by selectively increasing measurement cycles when confidence in distance change is detected.
Implementation Method 1
a time-of-flight imaging element... capable to detect single photons... the time of photon arrival is known
Data Source
AI summary
The present disclosure generally pertains to time-of-flight circuitry for determining a roundtrip delay of photons emitted by a light source and incident on a time-of-flight imaging element, the time-of-flight circuitry being configured to: determine a test number of photons at a test point of time and a reference number of photons at a reference point of time, the test point of time and the reference point of time being included in a measurement time interval of at least two measurement time intervals for which the test point of time is varied; and compare, for determining the roundtrip delay of the emitted photons, the test number of photons with the reference number of photons.