Automatic Gain Switching for X-ray Pixel Detector Dynamic Range
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Solution Overview
Problem
Current X-ray detector systems face inefficiencies at high photon flux rates due to signal overlap and saturation limitations, restricting their dynamic range and photon flux capabilities.
Innovation Solution
The implementation of a high-gain, low-noise readout system with automatic gain switching capabilities, allowing each pixel to dynamically adjust its gain based on the integrated charge, thereby extending the dynamic range and handling high photon flux without significant adjustments to frame rate or saturation levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a charge integrating system is used to extend count rate capabilities, then the maximum incoming flux increases, but the dynamic range is limited by the saturation level of the integrating preamp
Solution Approach 1:
The patent implements automatic gain switching that dynamically adjusts the amplifier gain based on the integrated charge level. The system transitions from a fixed gain architecture to a dynamic one where the gain is adjusted in real-time during the integration period, allowing the detector to adapt to varying photon flux conditions and extend the usable dynamic range beyond the fixed saturation point.
Solution Approach 2:
The invention changes the operating parameter (amplifier gain) during the measurement process. By switching between different gain settings based on the accumulated charge, the system can measure both low-flux and high-flux conditions within the same integration period, effectively expanding the dynamic range without requiring separate measurement modes.
2Productivity
If the frame rate is increased to handle higher photon rates, then the photon flux capability increases, but the data volume and power consumption increase
Solution Approach 1:
The automatic gain switching operates continuously during the integration period without requiring frame rate increases. The system maintains continuous monitoring and adjustment of the gain based on the integrated charge, allowing high photon flux handling within the existing frame rate structure, thereby avoiding the power consumption penalty associated with higher frame rates.
3Productivity
If the saturation level is increased to handle more photons, then the photon flux capability increases, but the feedback capacitor size must be increased which is limited by pixel area
Solution Approach 1:
Instead of statically increasing the capacitor size to raise the saturation level, the invention dynamically adjusts the effective saturation level by changing the amplifier gain. This allows the system to handle higher photon fluxes without requiring larger capacitors, as the gain adjustment effectively raises the saturation threshold in software rather than hardware.
4Productivity
If signal overlap is reduced to improve measurement accuracy, then the count rate capability improves, but the shaping time must be reduced which affects low flux sensitivity
Solution Approach 1:
The patent segments the measurement process into different gain phases. By using high gain for low-flux conditions and switching to low gain for high-flux conditions, the system can maintain single-photon resolution sensitivity when needed while handling high count rates when the flux is high, effectively segmenting the operational regimes to optimize both precision and productivity.
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 significantly increases the dynamic range and photon flux handling capacity, enabling detection of up to 2.4E8 photons per second per pixel without increasing power consumption, data volume, or degrading data quality, while maintaining single-photon resolution for low flux measurements.
Implementation Method 1
a layer of photosensitive material; an N×M array of photo-detector diodes arranged in said layer of photosensitive material; Each pixel in the sensor can be directly connected (bump bonding or flip chip bonding) to the corresponding pixel in the readout chip. The readout chip (ROC) contains an array of N×M independently working channels (pixels).
Data Source
AI summary
An X ray detector with single photon measurement capabilities includes a layer of photosensitive material and an N×M array of photo-detector diodes in the layer of photosensitive material. The photo-detector diodes have a bias potential interface and a diode output interface. An N×M array of high gain, low noise readout unit cells are assigned to the photo-detector diodes. Each readout unit cell has an input interface connecting the diode output interface to a high-gain charge-to-voltage amplifier with integration capacitors. The high-gain charge-to-voltage amplifier can switch between different gains. A comparator and a digital block monitors the charge of the integration capacitance and switches the gain depending from the monitored charge of the integration capacitance. The pixel detector provides the possibility of in pixel intermediate evaluation of an automatic gain switching circuit state to increase the dynamic range of the detector in case of quasi continuous incoming particle flux.