Silicon Drift Diode Detector Switching Between Pulse Height and Current Modes
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Solution Overview
Problem
Silicon Drift Diode (SDD) detectors are limited in count rate due to the time electrons take to reach the anode and the ballistic deficit effect, and they are not equipped to detect backscattered electrons (BSEs) with currents exceeding 1 pA, which can 'blind' the detector, necessitating the use of external windowing or deflection to avoid BSEs.
Innovation Solution
Incorporating a voltage/current converter between the I/O port and the anode with a switchable analog feedback loop allows the SDD to operate in either pulse height measurement mode or current measurement mode, enabling detection of BSEs without the need for reset and improving count rate capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the SDD is used to detect X-rays with high precision, then measurement precision is improved, but the count rate is limited due to electron drift time and ballistic deficit effect
Solution Approach 1:
The patent implements dynamic operation modes that can be switched based on detection needs. The SDD can operate in pulse height measurement mode for energy discrimination or in current measurement mode for high count rate applications, allowing the system to adapt its characteristics dynamically rather than being fixed in one operational state
Solution Approach 2:
The patent changes the operational parameters of the SDD by introducing a voltage/current converter and switchable feedback loop. By adjusting the feedback configuration and operating mode, the detector can optimize between energy resolution and count rate capability, effectively changing its performance characteristics to match the detection requirements
2Adaptability or versatility
If the SDD detects BSEs with current exceeding 1 pA, then detection capability is improved, but the detector becomes 'blinded' by the high electron current
Solution Approach 1:
The patent introduces a switchable feedback loop with a voltage/current converter that provides analog feedback to the SDD anode. This feedback mechanism stabilizes the detector operation under high electron currents by compensating for charge accumulation, preventing the detector from becoming blinded while maintaining reliable response
Solution Approach 2:
The voltage/current converter acts as an intermediary between the SDD and the readout electronics. It converts the charge signals from the SDD into voltage signals with appropriate scaling and impedance matching, enabling the detector to handle high BSE currents without saturation or blinding while maintaining signal integrity
3Reliability
If a window is added to block BSEs from reaching the detector, then detector reliability is improved, but device complexity increases
Solution Approach 1:
Instead of adding a physical window to block BSEs, the patent extracts and utilizes the BSE signals directly by operating the SDD in current measurement mode with appropriate feedback. This approach removes the need for additional physical components like windows or deflection elements, reducing device complexity while maintaining detector reliability
4Measurement precision
If external reset circuitry is used to reset the integrating capacitor, then measurement precision is maintained, but the count rate is further limited due to reset time
Solution Approach 1:
The patent merges the reset function with the signal readout path by implementing self-biasing reset through the FET drain leakage current. This integration eliminates the need for separate external reset circuitry and its associated dead time, allowing continuous operation at higher count rates while maintaining the ability to perform precise measurements through the voltage/current converter
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 configuration allows for selective detection of X-rays and electrons, enhancing the detector's ability to handle high BSE currents without being 'blinded' and maintaining performance in high-count rate scenarios.
Implementation Method 1
A SDD shows an active volume where impinging radiation, such as X-ray photons, generate electron-hole pairs
Implementation Method 2
As a result of the internal electric field in the diode the electrons drift to the anode where they charge the anode to a corresponding potential
Implementation Method 3
the voltage on the anode is converted into a voltage signal with appropriate scaling and impedance matching
Data Source
AI summary
A detector with a Silicon Diode and an amplifier, and a feedback element in the form of, for example, a resistor or a diode, switchably connected to the output of the amplifier. When the feedback element is selected via a switch, the detector operates in a Current Measurement Mode for determining electron current, and when the element is not selected the detector operates in its well-known Pulse Height Measurement Mode for determining the energy of X-ray quanta.