Geiger Mode Avalanche Photodiode Readout Circuit with Electronic Aperture
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Solution Overview
Problem
Conventional readout circuits for avalanche photodiodes are slow and unable to process high-frequency signals, making it difficult to distinguish measurement photons from interference events and ambient light, and they are insensitive during a dead time period, which limits their application in sensitive photodetection systems.
Innovation Solution
A light receiver with multiple avalanche photodiode elements biased in Geiger mode and associated readout circuits that include a measurement path and a blanking path, along with a switching element, allowing selective routing of the Geiger current to either path, enabling an electronic aperture to mask or differentiate regions, thereby simplifying reception optics and improving signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional readout circuits are used for avalanche photodiodes, then the circuit structure is simple, but the signal processing speed is slow and unable to process high-frequency signals
Solution Approach 1:
The readout circuit is segmented into multiple parallel paths (measurement path and blanking path) that can independently process signals from different avalanche photodiode elements. This segmentation allows simultaneous processing of multiple high-frequency signals without mutual interference, thereby increasing overall signal processing speed while keeping each individual path relatively simple.
Solution Approach 2:
The patent introduces a temporal dimension to the readout process by implementing time-multiplexed switching between measurement and blanking paths. This allows the system to process high-frequency signals by rapidly alternating between different signal acquisition modes, effectively increasing the processing bandwidth without requiring overly complex circuitry in each path.
2Measurement precision
If multiple avalanche photodiode elements are interconnected and statistically evaluated, then the detection sensitivity is improved, but the ability to associate light reception with specific triggering SPADs is lost
Solution Approach 1:
Each avalanche photodiode element is assigned a dedicated readout path that maintains a direct association between the detected signal and the triggering SPAD. This segmentation preserves spatial information and allows the system to identify which specific SPAD was triggered while still benefiting from the combined sensitivity of multiple elements.
Solution Approach 2:
The patent introduces switching elements as intermediaries between the avalanche photodiode elements and the measurement/blanking paths. These switches maintain the association between triggering SPADs and their corresponding signals by routing each SPAD's output through controlled paths, thereby preserving spatial resolution information while enabling flexible signal processing.
3Measurement precision
If the avalanche photodiode is biased above breakdown voltage for high sensitivity, then single photon detection capability is achieved, but interference events from ambient light and dark noise cannot be distinguished from measurement photons
Solution Approach 1:
The patent segments the signal processing into distinct measurement and blanking paths. The blanking path is specifically designed to capture and evaluate interference events from ambient light and dark noise, while the measurement path processes signals from the actual measurement photons. This segmentation allows the system to maintain high detection sensitivity while separately analyzing and filtering out interference components.
Solution Approach 2:
The system implements feedback mechanisms where the evaluation of interference events from the blanking path is used to adjust and optimize the measurement process. By continuously monitoring dark noise and ambient light interference through the blanking path, the system can adaptively compensate for these harmful factors, thereby maintaining high detection sensitivity while reducing the impact of interference.
4Productivity
If the avalanche diode is used during dead time for further measurements, then the measurement continuity is improved, but the signal accuracy deteriorates due to incomplete recovery
Solution Approach 1:
The patent segments the operational modes into distinct measurement and blanking periods, with controlled switching between them. This segmentation allows the system to alternate between high-precision measurement phases and recovery/blanking phases, ensuring that measurements are only taken when the avalanche diode has fully recovered, thereby maintaining signal accuracy while achieving measurement continuity through time-multiplexed operation.
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 allows for fast signal detection, reduced mechanical complexity, increased reliability, and cost-effective manufacturing, enabling the processing of high-frequency signals and distinguishing between triggered and untriggered regions, thus enhancing the sensitivity and accuracy of photodetection systems.
Implementation Method 1
In an avalanche photodiode (APD), the incident light triggers a controlled avalanche breakdown (avalanche effect). This multiplies the charge carriers generated by incident photons
Implementation Method 2
WO 2011/117309 A2 proposes to provide a third electrode on the SPAD detector element in addition to the anode and cathode for the providing the bias voltage, the third electrode being used for a capacitively coupled output of the Geiger current
Data Source
AI summary
A light receiver (100), comprising:a plurality of avalanche photodiode elements (10) each being biased with a bias voltage above a breakdown voltage and thus operated in a Geiger mode in order to trigger a Geiger current upon light receptionand a plurality of readout circuits (42, 44, 46) associated with individual avalanche photodiode elements (10) or a group of avalanche photodiode elements (10) for reading out a Geiger current generated upon light reception,wherein the readout circuits (42, 44, 46) each comprise a measurement path (42) and a blanking path (46) as well as a switching element (44) for selectively supplying the Geiger current, or a measurement current corresponding to the Geiger current, to the measurement path (42) or the blanking path (46).