Capacitor-Based Comparator for Photon Sensing Threshold Detection
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Solution Overview
Problem
In long-range time of flight applications, such as LiDAR, it is challenging to detect weak reflected light signals amidst high levels of ambient background light, which interferes with the ability to accurately sense objects like pedestrians in bright conditions.
Innovation Solution
A capacitor-based comparator is integrated into a threshold detection circuit within a photon sensing system, allowing for the effective measurement of return signals from photon sensors even in bright ambient light conditions, using Geiger-mode Single Photon Avalanche Diodes (SPADs) in pixel arrays to differentiate between signal and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodiodes are used in time of flight sensors to detect reflected light, then transfer efficiency from photo detection regions to sensing nodes is improved, but the ability to detect weak signals in high ambient light conditions deteriorates
Solution Approach 1:
The patent segments the detection process into multiple stages: photodiodes capture photons and generate signals, capacitors accumulate and integrate these signals over time, and comparators threshold the integrated signals. This segmentation allows each component to optimize its function, with the capacitor integration stage specifically designed to accumulate weak signal photons while averaging out random ambient light fluctuations, thereby resolving the contradiction between maintaining high transfer efficiency and achieving reliable detection in ambient light
Solution Approach 2:
The patent applies preliminary action by performing signal integration and accumulation in the capacitor stage before final threshold comparison. The capacitors pre-process the weak photon signals by integrating them over the measurement period, building up sufficient signal amplitude before the comparator stage. This preliminary integration ensures that weak reflected light signals reach detectable levels while ambient light noise remains statistically distributed, enabling reliable detection without sacrificing photodiode transfer efficiency
2Measurement precision
If multiple cameras are used for stereo imaging to create 3D images, then depth sensing capability is improved, but device complexity and processing requirements worsen
Solution Approach 1:
The patent replaces the mechanical/stereo imaging approach with a temporal measurement system. Instead of using multiple spatially separated cameras requiring complex triangulation calculations, the invention uses single-photon avalanche diodes with time-correlated single-photon counting to measure the time-of-flight of light. This substitution of mechanical stereo vision with temporal photon timing simplifies the device architecture while maintaining or improving depth sensing precision
Solution Approach 2:
The patent employs periodic action by using pulsed light illumination and time-gated photon detection. The system emits periodic light pulses and detects reflected photons within specific time windows corresponding to different depth ranges. This periodic temporal sampling approach enables 3D depth mapping with simplified hardware compared to continuous stereo imaging, reducing device complexity while preserving depth sensing capability
3Measurement precision
If signal integration time is increased to improve weak signal detection, then signal-to-noise ratio is improved, but real-time detection capability worsens
Solution Approach 1:
The patent applies preliminary action by pre-positioning and pre-charging multiple capacitors in parallel before the measurement interval begins. During the measurement window, these capacitors simultaneously integrate signals from their respective photodiodes. This preliminary preparation allows the system to perform parallel integration across multiple detection channels, achieving high signal-to-noise ratios through extended integration time while maintaining real-time capability through the parallel architecture that processes multiple time bins simultaneously
Solution Approach 2:
The patent transitions from temporal integration alone to a two-dimensional approach combining temporal integration with spatial parallelism. Multiple capacitors are arranged in a matrix corresponding to different photodiodes and different time bins. This dimensional expansion allows the system to integrate signals over extended time periods for high signal-to-noise ratio while simultaneously processing multiple depth ranges in parallel, thereby achieving both precision and real-time performance
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 solution enables accurate detection of objects in high ambient light environments by distinguishing a weak signal from a strong background, enhancing the capability to generate 3D images and determine depth information in real-time, even under conditions like bright sunlight.
Implementation Method 1
A capacitor-based comparator is integrated into a threshold detection circuit within a photon sensing system, allowing for the effective measurement of return signals from photon sensors
Implementation Method 2
using Geiger-mode Single Photon Avalanche Diodes (SPADs) in pixel arrays to differentiate between signal and noise
Data Source
AI summary
A threshold detection circuit includes a plurality of capacitors. A plurality of switching circuits is coupled to the capacitors such that a first end of each of the capacitors is coupled to a corresponding photon sensor during detection intervals, and the first end of each capacitor is coupled to a variable initialization value during reset intervals. A threshold number of the capacitors are initialized to a first value and the remaining capacitors are initialized to a second value during reset intervals. A comparator is coupled to a second of the capacitors to generate a detection event in response to the threshold number of photon sensors sensing one or more incident photons during detection intervals.