Preamplifier Feedback Control for Fast Reset and Low Noise
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Solution Overview
Problem
Existing preamplifier circuits for radiation detectors face challenges in achieving short reset periods and prompt resumption of normal operation after reset, often resulting in oscillations and increased noise due to high loop gain and slow reset times.
Innovation Solution
A preamplifier circuit design incorporating an amplifier, feedback capacitor, adjustable feedback circuit, and loop controller that selectively adjusts the transfer function and bias of the reset switch to manage operating modes, allowing for controlled reset periods and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a conventional reset switch is used to discharge the feedback capacitor, then the preamplifier can be reset, but the reset period becomes long and oscillations occur due to high loop gain
Solution Approach 1:
The patent applies dynamics by making the loop gain adjustable rather than fixed. The loop gain control circuit dynamically changes the gain value based on the operating mode (normal or reset), allowing the system to adapt its characteristics to different operational requirements. This resolves the contradiction by enabling fast reset (high gain during reset) while preventing oscillations (controlled gain during normal operation).
Solution Approach 2:
The patent changes the loop gain parameter based on the operating mode. During reset mode, the loop gain is increased to enable fast discharge of the feedback capacitor. During normal operation mode, the loop gain is reduced to prevent oscillations. This parameter change approach directly addresses the technical contradiction by optimizing the gain parameter for different operational phases.
2Speed
If the loop gain is increased to speed up reset, then the reset time decreases, but oscillations and noise increase
Solution Approach 1:
The loop gain is made dynamic rather than static, allowing it to take different values during reset mode versus normal operation mode. This dynamic adjustment enables the system to achieve fast reset speed when needed while suppressing oscillations and noise during normal operation, effectively resolving the contradiction between speed and harmful factors.
Solution Approach 2:
The system employs periodic switching between different gain states corresponding to reset mode and normal operation mode. During reset periods, high gain is applied temporarily to speed up capacitor discharge, then switched to low gain for normal operation. This periodic action pattern allows the system to achieve fast reset without sustained oscillations.
3Device complexity
If the reset switch bias is kept simple, then the device complexity is low, but the reset performance is slow and cannot be optimized
Solution Approach 1:
The reset switch bias voltage is changed based on the operating mode. During reset mode, the bias is adjusted to optimize the reset switch performance for fast discharge. During normal operation, the bias is set to minimize leakage and maintain stability. This parameter change approach improves reset speed without significantly increasing device complexity.
Solution Approach 2:
The loop gain control circuit serves multiple functions: it adjusts the loop gain for both oscillation control during normal operation and reset speed optimization during reset mode. The same control infrastructure is used for both purposes, improving reset performance without proportionally increasing device complexity.
Data Source
AI summary
Disclosed preamplifier circuit comprises amplifier arranged in first current path between input node and output node of the preamplifier circuit. Feedback capacitor is arranged in second current path between said input and output nodes. Feedback circuit having adjustable transfer function is arranged in third current path between said input and output nodes. Reset switch arranged in said third current path enables selectively coupling output of the feedback circuit to input of the amplifier and decoupling output of the feedback circuit from input of the amplifier. Loop controller is arranged selectively, in dependence of voltage in the preamplifier circuit, one of open reset switch to set preamplifier circuit in normal operating mode and close reset switch to set preamplifier circuit in reset mode. Loop controller is arranged to adjust the transfer function of the feedback circuit at least in part in dependence of the current operating mode of the preamplifier circuit.