Charge-Sensitive Amplifier Biasing for Stable Radiation Sensing
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Solution Overview
Problem
Existing charge sensitive amplifiers in radiation sensors experience significant variations in signal voltage due to PVT variations, leading to reduced sensitivity and longer discharge times, making high-speed sensing impractical.
Innovation Solution
A charge sensitive amplifier design that applies a bias direct current, rather than a DC voltage, to the gate of a feedback transistor, using a current mirror circuit insensitive to PVT variations, and employing a feedback MOS transistor in parallel with a feedback capacitor to minimize signal voltage fluctuations and expedite charging to a common voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC voltage is applied to the gate of the feedback transistor, then the feedback transistor can operate, but the signal voltage varies significantly due to PVT variations
Solution Approach 1:
The patent changes the biasing parameter from DC voltage to DC current. By applying a bias current to the gate of the feedback transistor instead of a DC voltage, the system becomes insensitive to PVT variations. The current mirror circuit generates a bias current that compensates for process, voltage, and temperature variations, thereby stabilizing the signal voltage and improving both reliability and measurement precision.
2Duration of action of stationary object
If a feedback resistor is used in the charge sensitive amplifier, then the output voltage can be charged to common voltage, but the layout area becomes large and signal voltage is small
Solution Approach 1:
The patent replaces the physical feedback resistor with an active feedback mechanism using a MOS transistor. Instead of relying on a large physical resistor to charge the output voltage to common voltage, the system uses a MOS transistor with bias current control. This substitution dramatically reduces the layout area while maintaining the charging function, and actually improves signal voltage by eliminating the parasitic resistance issues associated with large physical resistors.
3Adaptability or versatility
If the feedback transistor driving current changes according to PVT variations, then the transistor can adapt to different conditions, but the feedback resistance changes sensitively causing signal voltage variation
Solution Approach 1:
The patent implements a current mirror circuit that provides feedback to maintain stable bias current despite PVT variations. The current mirror monitors and adjusts the bias current to compensate for changes in process, voltage, and temperature. This feedback mechanism ensures that the feedback transistor operates with consistent current, stabilizing the feedback resistance and eliminating signal voltage variations while maintaining adaptability to different operating conditions.
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 reduces signal voltage variations and shortens charging time, enabling high-speed sensing by using a constant current from a bandgap reference circuit, resulting in more stable and efficient radiation detection.
Implementation Method 1
a feedback MOS transistor connected in parallel to the feedback capacitor between the first input terminal and the output terminal
Implementation Method 2
a feedback capacitor connected between the first input terminal and the output terminal
Data Source
AI summary
Disclosed are a charge sensitive amplifier capable of minimizing a variation in a signal voltage of an output signal by applying a bias direct current to a gate of a feedback transistor, and a radiation sensor including the same. According to the charge sensitive amplifier and the radiation sensor including the same, it is possible to minimize a variation in a signal voltage of a charge sensitive amplifier output signal by applying a current, which is formed by mirroring a current bias circuit designed to be insensitive to PVT variations, to a gate of a feedback transistor. Furthermore, it is possible to reduce a variation in charging time and enable high-speed sensing by charging the signal voltage to the level of a common voltage VCOM by using a constant current supplied through a bandgap reference (BGR) circuit.