Photon Counting Circuit for Charge-Sharing Error Correction
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Solution Overview
Problem
Photon counting devices face challenges in accurately counting photons due to charge sharing between neighboring pixels, leading to interpretation errors, especially in multiple-level detection systems where sensitivity and pixel size are critical.
Innovation Solution
A photon counting circuit with an analog pulse signal generation stage, a digital stage comprising comparators, a differentiating circuit, AND-type logic gates, and counters, where the differentiating circuit and comparators receive the same signal, and thresholds are incrementally adjusted to correct for stacking phenomena, allowing real-time counting without post-processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is decreased to improve sensitivity and avoid multiple photons being counted as a single high-energy photon, then measurement precision is improved, but charge sharing between neighboring pixels increases causing interpretation errors
Solution Approach 1:
The patent applies preliminary action by performing differentiation and sign detection on the pulse signal before the counting process. The circuit detects the derivative of the signal and identifies periods where the derivative maintains the same sign, which corresponds to individual photon interaction events. This preprocessing step distinguishes separate photon interactions even when their pulses overlap in time, preventing misinterpretation of multiple photons as a single high-energy photon and eliminating charge sharing errors between pixels.
2Measurement precision
If multiple-level detection is implemented to improve energy resolution, then measurement precision is improved, but device complexity increases due to multiple comparators and processing paths
Solution Approach 1:
The patent applies segmentation by dividing the energy detection range into multiple levels using several comparators, each with a different threshold value. Each comparator independently processes the differentiated signal to detect photons exceeding its specific energy threshold. This segmented approach allows multiple energy levels to be detected simultaneously through parallel comparison paths, maintaining measurement precision while organizing the complexity into manageable, modular segments.
Solution Approach 2:
The patent applies dynamics by using a differentiating circuit that dynamically processes the input signal in real-time. The derivative calculation and sign detection adapt to the temporal characteristics of each pulse signal, automatically adjusting to distinguish between single and multiple photon interactions based on the signal's instantaneous behavior. This dynamic processing enables the system to handle varying photon arrival patterns without requiring fixed, pre-configured processing paths for each scenario.
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
The solution effectively addresses stacking issues in photon counting, providing accurate photon counting in real-time across multiple energy levels, improving device resolution and reducing errors, while maintaining compatibility with existing systems and pixel sizes.
Implementation Method 1
a differentiating circuit for determining the periods when the derivative of the pulse signal has a same sign
Implementation Method 2
at least one first comparator of the amplitude of the pulses with respect to a first threshold
Implementation Method 3
at least one first AND-type logic gate for combining the outputs of the first comparator and of the differentiating circuit
Implementation Method 4
at least one first counter of the number of pulses present at the output of the combination element
Implementation Method 5
an analog pulse signal generation stage, each of the pulses of the pulse signal having an amplitude proportional to the energy released by an interaction of at least one photon in the detector
Data Source
AI summary
A circuit for counting photons, including: an input terminal intended to be connected to a detector of ionising radiation; an analogue stage for generating a pulsed signal, each pulse of which has an amplitude proportional to the energy released by an interaction of at least one photon in the detector; and a digital stage including: at least one first comparator for comparing the amplitude of the pulses to a first threshold; a differentiator circuit for determining periods in which the derivative of the pulse signal is of a given sign; at least one first logic gate for combining the outputs of the first comparator and the differentiator circuit; and at least one first counter for counting the number of pulses present on the output of the combining element.