SPAD Photon Counter with Peak Current Suppression for Accurate ToF
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Solution Overview
Problem
Existing image sensors face challenges in accurately determining time of flight (ToF) due to photon pileup and ambient noise, which distort histogram peaks, leading to large depth errors and increased power consumption.
Innovation Solution
A method involving a single photon avalanche diode (SPAD) controller with peak current suppression technique, utilizing coarse and fine histogram time to digital conversion (TDC) to enhance timing resolution and reduce power consumption, by generating coarse and fine histograms with different resolutions to accurately determine ToF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional histogram peak detection is used for ToF calculations, then additional hardware is required, but this increases device complexity and cost
Solution Approach 1:
The patent combines multiple histogram processing functions (peak detection, timing resolution enhancement, and distortion correction) into a single integrated circuit block within the image sensor. This merging eliminates the need for separate external hardware components while maintaining accurate ToF measurement capabilities through coordinated operation of histogram generation, peak detection, and refinement modules
Solution Approach 2:
The histogram processing circuit is designed to perform multiple functions simultaneously: generating histograms from photon detection events, detecting peak positions for ToF calculation, correcting histogram distortion from photon pileup, and enhancing timing resolution. This multi-functional approach replaces what would traditionally require multiple separate hardware components, reducing overall device complexity
2Reliability
If wider laser pulses are used for detection, then detection range is improved, but timing resolution is degraded
Solution Approach 1:
The patent segments the timing measurement process into multiple histogram bins that capture different time intervals. By dividing the time-of-flight range into discrete bins and analyzing the distribution of photon events across these bins, the system can detect wider laser pulses while maintaining timing resolution through the statistical analysis of the histogram peak position and shape
3Productivity
If ambient light photons are detected immediately after laser pulse transmission, then continuous detection is achieved, but histogram distortion occurs due to photon pileup
Solution Approach 1:
The patent applies preliminary anti-action by detecting and correcting histogram distortion before final ToF calculation. The system proactively identifies photon pileup effects through histogram analysis and applies correction algorithms to remove the distortion caused by ambient light photons detected immediately after laser pulses, thereby preserving measurement accuracy while maintaining continuous detection capability
Solution Approach 2:
The system uses feedback by continuously monitoring the histogram distribution and using the detected peak position and shape information to adjust and correct for photon pileup distortion. The histogram processing circuit analyzes the accumulated photon events and applies corrective measures based on the observed distortion patterns, improving histogram accuracy while maintaining continuous detection
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 improves ToF accuracy by reducing histogram distortion and power consumption, allowing for precise distance calculations without additional costly hardware.
Implementation Method 1
single-photon avalanche diode (SPAD) ends up capturing an ambient light photon
Data Source
AI summary
A sensor for time of flight calculation, including a laser configured to emit a plurality of pulses of light at a target, one or more SPADs configured to detect a TDC trigger event, where the first TDC trigger event includes one or more photons detected as an initial pulse of light of the plurality of pulses of light is reflected to the one or more SPADs, a counter configured to count the one or more photons of the first TDC trigger event and generate a first histogram of the one or more photons at a first resolution, a global window processor configured to read the first histogram and detect a peak of the first histogram, and a global histogram processor configured to detect a peak of the second histogram, wherein the peak of the second histogram determines a distance between the sensor and the target.