Avalanche Photodiode Random Number Generation for Sensor Interference
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Solution Overview
Problem
Existing distance-measuring sensors face ambiguities and mutual interference due to the reliance on complex pseudo-random number generators and the sensitivity to interference from extraneous light photons, which complicates object detection and distance measurement.
Innovation Solution
The use of avalanche photodiode elements as both measurement receiving elements and random generation elements, where the random generation elements are shielded from measurement light to utilize dark noise for generating random numbers, thereby reducing ambiguities and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pseudo-random number generators are used to vary timing behavior and encoding, then ambiguities and mutual interference between sensors are reduced, but device complexity increases significantly
Solution Approach 1:
The patent extracts the random number generation function from complex electronic circuits and relocates it to the physical layer by utilizing the inherent randomness of photon arrival times at SPAD elements. This eliminates the need for complex pseudo-random number generators while maintaining the ability to distinguish between sensors through unique timing patterns.
Solution Approach 2:
The system uses the natural quantum properties of light and the inherent timing jitter of SPAD detectors to generate random numbers automatically. The random number generation is a byproduct of the detection process itself, requiring no additional complexity or external random number generation circuits.
2Reliability
If multiple SPADs are evaluated together to limit interference from extraneous photons, then measurement reliability improves, but device complexity and processing requirements increase
Solution Approach 1:
The patent divides the detection task into two distinct functional segments: SPAD elements that are optically exposed to detect reflected light, and SPAD elements that are optically shielded to generate random numbers. This segmentation allows each group to perform its specialized function without interference, simplifying the overall evaluation process.
Solution Approach 2:
The patent introduces an optical shielding mechanism as an intermediary that physically separates the random number generation function from the measurement function. This mediator (optical shield) allows the system to maintain reliability through multiple SPAD evaluations while avoiding the complexity of processing interference from extraneous photons in the random number generation path.
3Measurement precision
If avalanche photodiodes are operated in Geiger mode with bias above breakdown voltage, then sensitivity to single photons is achieved, but susceptibility to interference from minimal events increases
Solution Approach 1:
The patent extracts the dark noise signal from the measurement path by using optically shielded SPAD elements. The dark noise events occur in these shielded elements and are used exclusively for random number generation, while the optically exposed elements focus solely on detecting reflected light without the confounding influence of dark noise.
Solution Approach 2:
The patent converts the harmful effect of dark noise events into a beneficial resource for random number generation. By directing dark noise events from shielded SPAD elements to seed random number generators, the system transforms what would normally be interference into a useful source of entropy for coding and modulation.
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 allows for the generation of reliable and simple random numbers, reducing sensor interference and ambiguities, and enabling unique coding for each sensor to prevent confusion between identical sensors.
Implementation Method 1
The incident light triggers a controlled avalanche breakdown (avalanche effect). This multiplies the charge carriers generated by the incident photons, resulting in a photocurrent that is proportional to the light reception intensity
Implementation Method 2
In this mode, the avalanche photodiode is biased above its breakdown voltage, so that even a single charge carrier released by a single photon can trigger an uncontrolled avalanche. Due to the high field strength, this avalanche then recruits all available charge carriers.
Implementation Method 3
Distance sensors based on the time-of-flight principle measure the travel time of a light signal, which corresponds to the distance via the speed of light
Implementation Method 4
in a phase-modulated method, the transmitted light is amplitude-modulated, and a phase shift between the transmitted and received light is determined, with the phase shift also serving as a measure of the light travel time
Data Source
Figure 1~2
Figure 3~4
AI summary
An optoelectronic sensor (10) for detecting objects (18) in a monitoring area (16) is described, comprising a light receiver (22) with a plurality of avalanche photodiode elements (24, 26), each of which can be biased with a voltage above a breakdown voltage and thus operated in a Geiger mode. At least one avalanche photodiode element is configured as a measuring receiver element (24) that receives measuring light (20) from the monitoring area (16). The sensor also includes an evaluation unit (28) configured to derive information about the objects (18) from the received signal of the measuring receiver element (24). At least one avalanche photodiode element is configured as a random number generator (26), and the evaluation unit (28) generates a random number from the received signal of the random number generator element (26).