Solid State Photomultiplier Subpixel Buffering
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Solution Overview
Problem
Conventional solid state photomultipliers (SSPMs) experience degraded readout pulse shape response due to increased parasitic capacitance and inductance as the size of the SSPM increases, leading to non-uniform gain and signal response across pixels.
Innovation Solution
The implementation of a silicon photomultiplier array with subpixels coupled to respective buffer amplifiers, allowing for multiplexed buffer amplifiers that can be monitored and adjusted to compensate for temperature and process nonuniformity, and disabled if necessary, thereby improving pulse shape readout without increasing the complexity of readout electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the size of the SSPM is increased to improve detection capability, then the number of pixels increases, but parasitic capacitance and inductance increase causing degraded pulse shape response
Solution Approach 1:
The patent divides each pixel into multiple subpixels (e.g., 2x2 or 2x3 grids) and assigns a dedicated buffer amplifier to each subpixel. This segmentation reduces the capacitance load on each buffer amplifier, maintaining fast rise times and improved pulse shape response while preserving the total detection capability of the larger SSPM array.
2Device complexity
If conventional buffer amplifiers are used for each pixel, then the circuit is simple, but the readout pulse shape exhibits slow rise time due to parasitic capacitance
Solution Approach 1:
Instead of using a single buffer amplifier per pixel, the patent segments each pixel into multiple subpixels, each with its own buffer amplifier. This reduces the effective capacitance seen by each amplifier, enabling faster rise times (e.g., <100 ps) while maintaining a relatively simple overall circuit architecture.
Solution Approach 2:
The patent introduces a hierarchical buffer amplifier structure with first-level buffers at the subpixel level and second-level buffers that aggregate signals from multiple subpixels. This multi-dimensional approach maintains fast response characteristics while managing the complexity of reading out large numbers of subpixels.
3Reliability
If buffer amplifiers are added to each subpixel to improve pulse shape, then the number of electronics increases, but the complexity of readout electronics becomes excessive
Solution Approach 1:
The patent combines multiple subpixel signals through hierarchical buffering, where first-level buffer amplifiers process individual subpixel signals and second-level buffer amplifiers aggregate these signals. This merging approach maintains the pulse shape benefits of individual subpixel buffering while reducing the total number of independent readout channels required.
Solution Approach 2:
The patent implements a two-level hierarchical buffer structure that adds a temporal and organizational dimension to the readout process. First-level buffers operate at the subpixel level for fast response, while second-level buffers provide signal aggregation and further processing, effectively managing complexity through structured organization rather than simple linear scaling.
4Reliability
If temperature variations occur, then gain uniformity degrades, but monitoring and adjustment mechanisms are needed
Solution Approach 1:
The patent incorporates monitoring circuitry that tracks the output signals from buffer amplifiers and provides feedback for detecting subpixel failures or performance degradation. This feedback mechanism enables real-time identification of problematic subpixels, allowing for compensation or disablement to maintain gain uniformity across the SSPM array.
Solution Approach 2:
The patent enables dynamic adjustment of buffer amplifier parameters (such as gain or bias voltage) in response to monitored conditions. By changing these parameters based on temperature variations or subpixel performance, the system maintains uniform gain across all pixels without requiring complex external calibration systems.
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 enhances the pulse shape response and maintains uniform gain and signal response across SSPM subpixels, effectively addressing the degradation issues caused by increased parasitic capacitance and inductance, while allowing for continuous monitoring and adjustment to compensate for temperature variations.
Implementation Method 1
The Silicon Photomultiplier (SiPM) is a multipixel array of avalanche photodiodes with a number up to a few thousand independent micropixels
Data Source
AI summary
Embodiments of a solid state photomultiplier are provided herein. In some embodiments, a solid state photomultiplier may include a plurality of pixels, wherein each pixel of the plurality of pixels comprises a plurality of subpixels; and a first set of buffer amplifiers, wherein each buffer amplifier of the first set of buffer amplifiers is respectively coupled to a subpixel of the plurality of subpixels.