Pulse Shaper Circuit for Direct Conversion Detector
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Solution Overview
Problem
Direct conversion radiation detectors face the ballistic deficit effect, leading to noise and image quality issues in computed tomography systems due to variations in output pulse amplitudes for X-rays of the same energy, which existing solutions fail to adequately address.
Innovation Solution
A pulse shaper circuit with an integrator amplifier, feedback capacitance, and switching units that control the feedback circuit to remove the discharge resistance when the output signal exceeds a threshold, allowing for the integration of a substantial part of the signal and subsequent discharge of the feedback capacitance, thereby reducing the ballistic deficit effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a feedback discharge unit is used to reduce ballistic deficit, then output pulse amplitude consistency improves, but device complexity increases due to additional control units and switching mechanisms
Solution Approach 1:
The feedback discharge control is segmented into discrete operational states: a feedback discharge state where the switching unit connects the feedback resistance to discharge the feedback capacitance, and a feedback hold state where the switching unit disconnects the feedback resistance. This segmentation allows precise control over the timing and duration of feedback discharge, improving output pulse amplitude consistency while maintaining manageable circuit complexity through clear state transitions.
Solution Approach 2:
The feedback resistance is made dynamically controllable through a switching unit that can change its connection state based on the integration signal characteristics. The switching unit transitions between connecting and disconnecting the feedback resistance from the feedback capacitance, enabling adaptive adjustment of the feedback discharge process. This dynamic control allows the system to optimize ballistic deficit compensation in real-time without requiring permanently complex circuitry.
2Object-affected harmful factors
If the feedback resistance is continuously active, then noise reduction improves, but ballistic deficit increases due to continuous discharge of feedback capacitance
Solution Approach 1:
The feedback discharge occurs periodically rather than continuously. The switching unit activates the feedback resistance only during specific time windows when discharge is beneficial, then disconnects it to prevent excessive discharge. This periodic activation pattern allows the system to reap the noise reduction benefits of feedback discharge while avoiding the ballistic deficit problems associated with continuous discharge, achieving a temporal balance between the two competing requirements.
Solution Approach 2:
The system uses feedback control where the state of the switching unit is determined by monitoring the integration signal and feedback capacitance voltage. When the feedback capacitance voltage reaches a threshold indicating sufficient charge accumulation, the switching unit activates to discharge the capacitance through the feedback resistance. This feedback mechanism ensures discharge occurs at optimal moments, reducing noise while preventing excessive discharge that would cause ballistic deficit.
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 reduces the ballistic deficit effect, improving image quality by providing output pulses that are more proportional to the energy of the detected radiation and reducing image artifacts in medical imaging systems.
Implementation Method 1
an amplifier with an amplifier input connected to the shaper input and an amplifier output connected to the shaper output. The amplifier is configured as an integrator
Implementation Method 2
There is a feedback capacitance between the input and the output of the amplifier
Implementation Method 3
a feedback circuit connected in parallel with the feedback capacitance or with the input and output of the amplifier. The feedback circuit may be a current source in some examples or a discharge resistance
Implementation Method 4
A second switching unit may be connected to the input and output of the amplifier, when the second switching unit is closed the second switching unit functions as a short circuit to rapidly reset the integrator or equivalently discharge the feedback capacitance
Data Source
AI summary
Disclosed herein is a radiological instrument (100, 200, 300, 400, 600, 700, 800) comprising at least one pulse shaper circuit (102) configured for a direct conversion radiation detector (108). The at least one pulse shaper circuit comprises an amplifier (110). The pulse shaper further comprises a feedback circuit (118) connected in parallel with the amplifier; a first switching unit (120) connected in series with the feedback circuit; a second switching unit (122) connected in parallel with the amplifier; a discriminator circuit (124) that provides a discriminator signal (128) when the output exceeds a controllable signal threshold; and a control unit (124) for controlling the first switching unit and the second switching unit, wherein the control unit controls the second switching unit such that a substantial part of the signal is integrated, when the second switching unit is closed.