Pulse Processing for X-ray Detectors with Noise Estimation
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Solution Overview
Problem
Existing methods for analyzing analogue signals in high-count rate scenarios, such as X-ray detection, provide less reliable event height estimates due to high variance caused by noise sources, especially when the time between events is small.
Innovation Solution
A noise contribution model is used to estimate and subtract noise from the signal integration over a specific time interval, leveraging samples before and after the event to improve the accuracy of event height estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If signal integration time is increased to reduce variance in signal level estimates, then measurement precision improves, but noise contributions from low-frequency noise and leakage increase
Solution Approach 1:
The patent divides the signal processing into two distinct pathways: a fast pathway that processes individual pulses with short integration time to capture high-count rate events, and a slow pathway that processes baseline drift with long integration time to remove low-frequency noise. This segmentation allows each pathway to be optimized for its specific function without compromise.
Solution Approach 2:
The patent introduces an intermediary processing stage where the fast pathway output is corrected by the slow pathway output. The slow pathway acts as a mediator that estimates and removes baseline drift from the fast pathway signal, enabling accurate pulse height measurement even in the presence of low-frequency noise.
2Productivity
If counting rate is increased to improve productivity, then output per unit time improves, but event height estimation reliability deteriorates due to high variance from noise
Solution Approach 1:
The patent implements dynamic signal processing where the integration time and filtering parameters are adaptively adjusted based on the instantaneous count rate. When count rate is high, the fast pathway uses shorter integration times to capture events before they overlap, while the slow pathway continuously adapts to remove the resulting baseline fluctuations, maintaining measurement reliability across varying productivity levels.
3Productivity
If integration time is shortened to capture high count rate events, then productivity improves, but measurement precision deteriorates due to high variance in signal level estimates
Solution Approach 1:
The patent merges the outputs of two processing pathways: the fast pathway provides timely detection of high-count rate events with short integration, while the slow pathway provides precise baseline estimation with long integration. By combining these complementary results, the system achieves both high productivity and measurement precision that neither pathway could achieve alone.
Data Source
AI summary
The invention relates to a method for analyzing an analogue signal comprising randomly spaced events having an event height. The method includes irradiating a sample with a focused beam of energetic electrons, detecting emission from the sample in response to such irradiation, and converting an analog signal of the emissions to a stationary time signal. The method further includes determining an estimated noise contribution for the stationary time signal, and determining an estimated event height of an event based on the stationary time signal and the estimated noise contribution for the stationary time signal, and determining, based on the estimated event height, an energy of the emission detected by the detector. This method is particularly useful for X-ray detectors, such as Silicon Drift Detectors, used in a SEM. By estimating the noise contribution to the signal, the step height is estimated with improved accuracy.