Pseudo Resistor Circuit Stabilizing Charge Amplifier
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Solution Overview
Problem
Existing charge amplifier circuits require high-resistance elements, which increase circuit size and are sensitive to manufacturing variations, power supply changes, and temperature, leading to non-linearity and waveform distortion.
Innovation Solution
A pseudo resistor circuit using a pair of matched field effect transistors with a voltage dividing circuit and operational amplifiers to stabilize the pseudo resistance value, eliminating the need for additional adjustment circuits and reducing waveform distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high-resistance element is mounted in the charge amplifier to reduce cutoff frequency, then the low-frequency detection capability is improved, but the circuit size increases
Solution Approach 1:
The patent changes the operating region parameter of the MOSFET from strong inversion to weak inversion, which fundamentally alters the resistance characteristics. By operating in the weak inversion region, the MOSFET exhibits exponentially high resistance values that enable low cutoff frequency without requiring large physical resistors, thus resolving the contradiction between low-frequency capability and circuit size
Solution Approach 2:
The patent substitutes physical high-resistance elements with an active MOSFET circuit operating in weak inversion. This replacement uses the transistor's inherent exponential current-voltage relationship in weak inversion to generate equivalent high resistance, eliminating the need for large physical resistors and reducing circuit area while maintaining the required electrical characteristics
2Manufacturing precision
If a MOSFET is used as a pseudo resistor in the weak inversion region, then the resistance value is exponentially varied depending on oxide film capacity and voltage factors, but this makes the resistance value very sensitive to manufacturing variations and power supply changes
Solution Approach 1:
The patent introduces feedback mechanisms through operational amplifiers that monitor and adjust the MOSFET gate voltage to compensate for variations. The feedback circuit detects changes in resistance due to manufacturing variations or power supply fluctuations and dynamically adjusts the gate voltage to maintain a stable effective resistance value, thereby resolving the sensitivity issue
Solution Approach 2:
The patent makes the MOSFET resistance dynamically adjustable through gate voltage control. By using dynamic voltage adjustment via feedback circuits, the system can compensate for manufacturing variations and environmental changes in real-time, transforming the static sensitivity problem into a dynamically manageable parameter
3Adaptability or versatility
If an adjustment circuit is added to control the gate voltage of the MOSFET, then the pseudo resistance value can be adjusted, but the device complexity increases
Solution Approach 1:
The patent designs the operational amplifier circuits to serve multiple functions: they provide feedback for stability, enable resistance adjustment, and compensate for variations. By making these circuits multi-functional, the patent avoids adding separate dedicated adjustment circuits, thus achieving adaptability without proportionally increasing complexity
Solution Approach 2:
The patent merges the resistance adjustment function with the existing feedback and amplification circuits. The same operational amplifiers that provide signal amplification also control the MOSFET gate voltage to adjust resistance, combining multiple functions into unified circuit blocks and reducing overall device complexity
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
The pseudo resistor circuit stabilizes the pseudo resistance value, reducing waveform distortion and allowing for reliable amplification of low-frequency signals while minimizing circuit size and integration challenges.
Implementation Method 1
a first field effect transistor Ma which functions as a pseudo resistor and has a drain terminal D, a source terminal S, and a gate terminal G
Data Source
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AI summary
A pseudo resistor circuit and a charge amplifier each include a first field effect transistor (Ma); a second field effect transistor (Mb) having electrical characteristics matched with electrical characteristics of the first field effect transistor (Ma); a voltage dividing circuit (21) in which one terminal of a reference resistor (Rstd) is electrically connected to a source terminal of the second field effect transistor; a first operational amplifier (OP1) an output terminal of which is connected to a gate terminal of the first field effect transistor and a gate terminal of the second field effect transistor and in which midpoint voltage of the voltage dividing circuit is input into one of an inverting input terminal and a non-inverting input terminal and reference voltage is input into the other of the inverting input terminal and the non-inverting input terminal; and a second operational amplifier (OP2) that supplies voltage resulting from inversion and amplification of drain voltage of the first field effect transistor into the other terminal of the reference resistor.