Series-Coupled Photodetector Grid for Scalable Position Sensing
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Solution Overview
Problem
Conventional position-sensitive photodetector arrays face limitations in scalability due to high capacitance, leading to reduced bandwidth and spatial resolution, particularly in large-area applications such as gamma cameras, where accurate localization of gamma rays is critical for medical imaging.
Innovation Solution
A photodetector grid is designed with horizontal and vertical arrays of photodetectors electrically coupled in series, forming an alternating sequence to reduce effective capacitance and enhance temporal resolution, allowing for high spatial and temporal resolution without the need for common connections that limit scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the photosensitive area of the SiPM is increased to improve detection coverage, then the capacitance increases, resulting in reduced bandwidth and degraded timing performance
Solution Approach 1:
The patent divides the photodetector array into multiple smaller photodetector elements connected in series, where each element has low capacitance. This segmentation allows the total photosensitive area to be large while maintaining low effective capacitance, thus preserving high bandwidth and timing performance.
Solution Approach 2:
The patent transitions from parallel connection topology to series connection topology, fundamentally changing the electrical dimension of the array configuration. This series connection arrangement transforms the capacitance scaling behavior from additive (parallel) to divisive (series), enabling large area with low effective capacitance.
2Measurement precision
If the photodetector array size is increased to improve spatial resolution, then the circuitry complexity and power dissipation increase, making it prohibitive for large-area applications
Solution Approach 1:
The patent segments the large photodetector array into multiple smaller elements that can be independently connected in series, reducing the need for complex individual readout circuits for each element. This segmentation strategy simplifies the overall circuitry while maintaining high spatial resolution through the series connection architecture.
3Device complexity
If larger-area photodetectors are used to reduce the number of readout circuits, then the capacitance increases, causing signal distortion and reduced bandwidth
Solution Approach 1:
Instead of using fewer large photodetectors, the patent segments the detection area into multiple smaller photodetectors connected in series. This maintains signal fidelity by keeping individual element capacitances low while achieving large total area, avoiding the signal distortion that would result from using fewer large elements.
Solution Approach 2:
The patent merges multiple low-capacitance photodetector elements in series to create a large-area detector with low effective capacitance. This combining strategy achieves the area reduction benefit while preserving signal fidelity, as the series connection prevents the capacitance addition problem that would occur with parallel connections.
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 configuration maintains high temporal resolution and reduces signal propagation delays, enabling improved spatial resolution and scalability in large photodetector arrays, particularly in applications like positron emission tomography (PET) and gamma cameras.
Implementation Method 1
Photodetectors are used to sense light or other electromagnetic radiation
Implementation Method 2
larger-area SiPMs suffer from large capacitance (e.g., 5-50 nF/cm2), and therefore low bandwidth and low signal amplitudes
Data Source
AI summary
A position-sensitive photodetector device includes a grid of series-connected photodetectors that are electrically coupled to either a vertical photodetector array (VA photodetectors) or to a horizontal photodetector array (HA photodetectors). The VA and HA photodetectors are arranged in an alternating sequence along rows and/or columns throughout the grid. A horizontal-position readout line is electrically coupled to a termination of each vertical photodetector array, and a vertical-position readout line is electrically coupled to a termination of each horizontal photodetector array.