X-ray Detector Readout Chip for Single Photon Resolution
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Solution Overview
Problem
Current X-ray detectors face limitations in frame rate due to significant readout time, analogue signal pileup at high photon rates, charge sharing between channels, and inability to perform simultaneous measurements in non-constant conditions, especially at high photon frequencies and in pump and probe applications.
Innovation Solution
A charge integrating system is employed instead of single photon counting, integrating charge on a capacitor and allowing continuous acquisition with low noise, enabling single photon counting resolution and interpolation of photon position, and using multiple counters for enhanced data processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single photon counting system is used, then single photon resolution is achieved, but readout time causes significant dead time limiting frame rate
Solution Approach 1:
The readout process is segmented into two independent phases: acquisition mode where counters count incoming photons, and readout mode where counting is disabled and count values are read out. This segmentation allows the acquisition to continue in parallel with readout operations on other channels, reducing the effective dead time per channel while maintaining single photon counting capability.
Solution Approach 2:
The system maintains continuous photon counting across all channels by rapidly switching between readout modes for different channels. While one channel is being read out, other channels continue acquiring photons, ensuring that the useful action of photon detection continues without interruption across the detector array, thereby reducing overall dead time.
2Measurement precision
If single photon counting system is used, then photon counting capability is achieved, but analogue signal pile up occurs at high photon rates
Solution Approach 1:
The system performs preliminary action by rapidly switching between acquisition and readout modes before signal pileup can occur. The readout operation is initiated in advance for channels that have accumulated sufficient counts, preventing the analogue signal from staying continuously above the comparator threshold and causing saturation.
Solution Approach 2:
The system implements periodic switching between acquisition mode and readout mode for each channel. This periodic action ensures that even at high photon rates, there are regular intervals where the counter is read out and reset, preventing continuous signal accumulation and maintaining accurate photon counting capability.
3Manufacturing precision
If small pixel size is used, then detector resolution is improved, but charge sharing between channels increases
Solution Approach 1:
The system uses feedback from the counted photon events to adjust and optimize the readout timing for adjacent channels. By monitoring the count rates and signal characteristics, the system can dynamically adjust the acquisition and readout schedule to minimize charge sharing effects between adjacent small pixels, maintaining measurement precision despite reduced pixel size.
4Device complexity
If internal counter is used for accumulation, then photon counting is simplified, but simultaneous measurements in different conditions are impossible
Solution Approach 1:
The single internal counter is segmented in time through rapid switching between acquisition modes for different measurement conditions. The counter can be allocated to different measurement channels (e.g., pumped and unpumped states) in alternating time intervals, enabling simultaneous measurements of multiple conditions using the same physical counter resource.
Solution Approach 2:
The system dynamically switches the counter between different acquisition modes and measurement conditions based on the experimental requirements. This dynamic allocation allows the same counter to participate in multiple simultaneous measurement scenarios by rapidly changing its operational state, enhancing system versatility without increasing hardware complexity.
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 extends count rate capability, improves spatial resolution, and allows simultaneous measurements by reducing dead time and analogue signal pileup, enabling accurate single photon counting and energy resolution across a wide dynamic range.
Implementation Method 1
the free load generated by the photon absorption can also range within appropriate and determinable limits
Data Source
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Figure 3~4
AI summary
According to the present invention, an X-ray detector is disclosed, comprising: a) a layer of photosensitive material (4); b) an NxM array of photo-detector diodes (2) arranged in said layer of photosensitive material (4); each of said photo-detector diodes (2) having a bias potential interface (12) and a diode output interface, said bias potential interface (12) of each photo-detector diode (2) being connected to a bias potential (V bias ); c) an NxM array of high gain, low noise readout unit cells (RO), one readout unit cell (RO) for each photo-detector diode (2); d) each readout unit cell (RO) comprising: d1) an input interface (IN) connected to said diode output interface, a high-gain voltage amplifying means (PA) comprising an integration capacitor (C fb ), d2) a first switch (S1) in parallel to the integration capacitor (C fb ), d3) a sample/hold capacitor (C S ) disposed between a second switch (S2) and third switch (S3), wherein the sample/hold capacitor (C S ) is connectable to an output (OUT) of the high-gain voltage amplifying means (PA) via the second switch (S2) and is connectable to a signal output line (SO) via the third switch (S3); e) a multiplexing means (MM) comprising a row select and a column select circuit allowing to access each readout cell unit (RO), i.e. to read out the analog signal as actually stored in the sample/hold capacitor (C S ) to a data processing means (DPM) controlling the multiplexing means.