Common-Source MEMS Sensor Preamplifier With Stable Low-Noise Gain
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Solution Overview
Problem
Existing preamplifiers for MEMS capacitive sensors suffer from high flicker noise, large power consumption, and temperature-dependent gain variations due to the use of operational amplifiers and positive feedback circuits.
Innovation Solution
A low noise, low power preamplifier circuit utilizing a charge pump, a single-ended common-source amplification configuration with negative feedback, and a gate voltage compensation circuit to maintain MOSFETs in saturation and reduce temperature dependencies, while employing a charge pump filter resistor and anti-parallel diodes for biasing and feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If operational amplifiers are used to realize preamplifiers, then gain functionality is achieved, but flicker noise increases and power consumption increases
Solution Approach 1:
The patent extracts and removes the operational amplifier component from the preamplifier circuit, replacing it with a simplified circuit using only a MOSFET, capacitors, and resistors. This elimination of the operational amplifier simultaneously reduces both power consumption and flicker noise generation, as the harmful effects were inherent to the operational amplifier's internal MOSFET structure.
Solution Approach 2:
The patent replaces the complex, power-hungry operational amplifier with a simpler, lower-cost circuit configuration using basic components (single MOSFET, capacitors, resistors). This substitution achieves the required preamplification function with significantly reduced power consumption and noise, effectively using a simpler alternative to replace the complex original design.
2Area of stationary object
If operational amplifiers are used to realize preamplifiers, then gain functionality is achieved, but silicon area increases
Solution Approach 1:
The patent removes the operational amplifier block from the circuit design, replacing it with a compact arrangement of individual components (one MOSFET, several capacitors, and resistors). This extraction significantly reduces the silicon area required while also reducing power consumption, as the operational amplifier's large internal transistor structure is eliminated.
Solution Approach 2:
The patent combines multiple functions (amplification, biasing, and signal conditioning) into a single integrated circuit stage using a MOSFET with associated passive components. This merging of functions into a compact configuration reduces the overall silicon area compared to using separate operational amplifier blocks for each function.
3Stability of the object's composition
If positive feedback through capacitors is used to achieve gain, then gain functionality is achieved, but gain varies drastically with temperature
Solution Approach 1:
The patent employs negative feedback through capacitors connected between the drain and gate of the MOSFET, rather than positive feedback. This negative feedback mechanism stabilizes the gain against temperature variations by automatically adjusting the operating point, while the feedback network using capacitors and resistors maintains accurate gain control across temperature ranges.
Solution Approach 2:
The patent uses temperature-compensated biasing circuits and carefully selected capacitor values that maintain stable gain characteristics across temperature variations. By adjusting and optimizing the parameters of the feedback network (capacitor ratios, resistor values), the circuit achieves temperature-independent gain performance.
Data Source
AI summary
A common source preamplifier for a MEMS capacitive sensor is disclosed. The preamplifier is a single-stage amplifier employing negative feedback. The preamplifier provides stable gain independent of temperature and at the same time provides effective buffering for a subsequent stage. Further, the preamplifier may be configured to provide different values of gain. Furthermore, the preamplifier has lower noise and consumes lesser area and lesser power than prior art.