Feedback Amplifier Circuit for Low-Noise High-Linearity Sensing
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Solution Overview
Problem
Conventional low noise amplifier circuits face challenges in achieving high accuracy, high linearity, and low noise levels while maintaining low power consumption, especially when amplifying small signals from sensors, and require high input impedance.
Innovation Solution
The amplifier circuit employs a series connection of PMOS and NMOS transistors with feedback loops and resistor networks, along with a current conveyer circuit to enhance signal-to-noise ratio and linearity, using differential pairs and low voltage threshold transistors to achieve improved noise reduction and power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional feedback loops are used to ensure high accuracy and linearity, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The feedback loop is segmented into two independent loops: a main feedback loop for accuracy and a peaking loop for linearity. Each loop has its own feedback path with dedicated components (main feedback capacitor Cmf, peaking feedback capacitor Cpf), allowing independent optimization of accuracy and linearity without increasing overall system complexity
Solution Approach 2:
The peaking capacitor Cpf is configured to be variable rather than fixed, allowing dynamic adjustment of the peaking loop's feedback strength. This enables the system to adaptively optimize linearity under different operating conditions while maintaining the simplicity of the feedback structure
2Measurement precision
If low noise level is achieved through additional circuit components, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The peaking loop is merged with the main feedback loop by sharing common components such as the operational amplifier, input transistor, and feedback resistor Rf. The peaking capacitor Cpf is connected in parallel with the main feedback capacitor Cmf, creating a unified feedback structure that achieves noise reduction without requiring separate independent circuits
Solution Approach 2:
The feedback network serves dual functions: the main feedback path (through Cmf and Rf) provides accuracy and gain control, while the peaking path (through Cpf) simultaneously optimizes linearity and reduces noise. This multi-functionality is achieved within a single feedback loop structure, avoiding additional power-consuming circuits
3Measurement precision
If high input impedance is maintained for sensor signals, then measurement precision is improved, but device complexity increases
Solution Approach 1:
A buffer stage using a voltage follower configuration (operational amplifier connected with feedback from output to inverting input) is introduced between the high-impedance sensor source and the main amplifier circuit. This buffer acts as an intermediary that maintains the high input impedance required by the sensor while isolating the sensor from the complex feedback network, preventing impedance loading without requiring direct complex circuitry at the sensor interface
Data Source
AI summary
An amplifier circuit includes a circuit path of serially connected complementary type transistors. First and second feedback loops include a loop amplifier, the transistors of the circuit path and a corresponding resistor.