Photon Counting Detector Pixel Dark Current Compensation
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Solution Overview
Problem
Existing energy-resolving photon counting detectors face challenges in accurately compensating for dark current, especially at higher photon incidence rates, leading to measurement errors and potential saturation of the charge sensitive amplifier (CSA).
Innovation Solution
A detector pixel with a dark current compensation unit (DCCU) that utilizes a signal following unit to provide an intermediate signal with asymmetric response characteristics, allowing for accurate estimation and compensation of dark current while mitigating the effect of signal pulses from incident photons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low-pass filter architecture is used for dark current compensation, then the dark current can be estimated and compensated, but at higher photon incidence rates the signal average is further removed from the baseline value causing mismatch between estimated and actual dark current
Solution Approach 1:
The patent implements dynamic dark current compensation by adjusting the compensation signal based on the actual operating conditions. The system dynamically adapts the compensation amount using a scaling factor that accounts for the ratio between actual and estimated dark current, allowing the compensation to remain accurate across varying photon incidence rates and operational states.
Solution Approach 2:
The patent employs feedback mechanisms to improve dark current compensation accuracy. The system monitors the CSA output signal, estimates dark current using low-pass filtering, compares it with actual dark current measurements, and adjusts the compensation signal accordingly. This closed-loop feedback ensures accurate compensation even at high photon incidence rates where static compensation methods fail.
2Measurement precision
If dynamic dark current compensation is implemented to account for varying dark current, then compensation accuracy improves, but circuit complexity increases
Solution Approach 1:
The patent achieves dynamic dark current compensation using existing circuit components with multiple functions. The low-pass filter serves both signal conditioning and dark current estimation purposes. The CSA output signal is reused for both energy measurement and dark current compensation calculations. This multi-functional approach implements dynamic compensation without requiring entirely separate dedicated circuits, thereby limiting the increase in overall device complexity.
Solution Approach 2:
The patent implements dynamic compensation by changing operational parameters rather than adding complex hardware. The system adjusts the dark current compensation signal magnitude using a scaling factor that varies with operating conditions. By modifying signal parameters and gain values dynamically, the system achieves adaptive compensation while maintaining relatively simple circuit architecture.
3Quantity of substance
If the CSA integrates dark current over time, then the dark current contribution accumulates, but the output voltage may exceed the supply voltage causing saturation
Solution Approach 1:
The patent applies preliminary anti-action by implementing dark current compensation before the CSA output voltage reaches saturation levels. The system continuously estimates and subtracts the dark current contribution from the CSA output signal, preventing the accumulated dark current charge from driving the output voltage beyond the supply voltage limits. This proactive compensation maintains CSA operation within the linear region.
Solution Approach 2:
The patent extracts the dark current component from the total CSA output signal through low-pass filtering and separate processing. By isolating and removing the dark current contribution before it accumulates to saturation levels, the system prevents the harmful effect of dark current integration while preserving the useful signal information for energy measurement.
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 proposed solution enables more accurate dark current compensation and improved measurement accuracy by effectively distinguishing between dark current changes and signal pulses, thus enhancing the energy resolution of the detector pixel.
Implementation Method 1
a photodetector configured to convert an incident photon into a first signal indicative of an energy of the incident photon
Data Source
AI summary
The present disclosure relates to a detector pixel for an energy-resolving photon counting detector, and to a photon counting detector comprising the same. The pixel comprises: a photodetector configured to convert an incident photon into a first signal indicative of an energy of the incident photon; a charge sensitive amplifier (CSA) configured to convert the first signal at an input of the CSA into a CSA output signal at an output of the CSA; and a dark current compensation unit (DCCU) for compensating a dark current of the photodetector. The DCCU comprises a signal following unit configured to provide an intermediate signal that is configured to follow a signal indicative of the CSA output signal, with a first maximum signal change rate in a first direction and a second maximum signal change rate, lower than the first maximum signal change rate, in a second direction opposite the first direction, wherein the second direction is a direction in which the signal indicative of the CSA output signal is configured to change when a photon is incident on the photodetector. The DCCU further comprises a signal generation unit configured to generate a dark current compensation signal based on the intermediate signal and to provide said dark current compensation signal to the CSA.