Current-Feedback Instrumentation Amplifier for Low-Noise MEMS Readout
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Solution Overview
Problem
Current MEMS and NEMS-based gyroscopes face challenges in achieving navigation-grade performance due to high noise and power consumption, particularly in the front-end amplifier stage, which is incompatible with monolithic integration and stable temperature requirements.
Innovation Solution
A modified current-feedback instrumentation amplifier (CFIA) is developed, eliminating degeneration resistances to reduce noise sources, featuring a differential pair of transistors connected directly to a differential voltage amplifier and bias current sources without degeneration resistors, optimizing power and noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional instrumentation amplifier is used with high current level to satisfy noise requirements, then noise performance is improved, but monolithic integration becomes incompatible due to power dissipation
Solution Approach 1:
The patent changes the fundamental operating parameters of the instrumentation amplifier by transitioning from a conventional voltage-feedback architecture to a current-feedback architecture. This parameter change allows the amplifier to achieve navigation-grade noise performance (below 50 nV/√Hz) at significantly lower current levels (1-10 µA), resolving the contradiction between noise performance and power consumption that prevented monolithic integration
2Stability of the object's composition
If degeneration resistances are used in the input and feedback transimpedance amplifiers, then circuit stability is improved, but noise performance deteriorates due to additional noise sources
Solution Approach 1:
The patent extracts and removes the degeneration resistances from the input and feedback transimpedance amplifiers. By taking out these noise-generating components, the invention achieves ultra-low noise performance suitable for navigation-grade sensors while maintaining circuit stability through the current-feedback architecture and appropriate compensation techniques
3Device complexity
If a pseudodifferential amplifier architecture is used to embed sensing gauges, then device complexity is reduced, but noise performance is insufficient for navigation grade applications
Solution Approach 1:
The patent creates a universal current-feedback instrumentation amplifier architecture that can accommodate various sensing configurations including embedded sensing gauges. The multi-functional design allows the amplifier to work with different sensor types (capacitive, piezoresistive, piezoelectric) while maintaining navigation-grade noise performance, thus achieving both low complexity and high precision
Data Source
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AI summary
A monolithically-integrated current-feedback instrumentation amplifier comprising two differential pairs of transistors (M1, M2) and (M3, M4). A drain terminal of transistor (M1) is directly connected to a drain terminal of transistor (M3) and to a differential voltage amplifier (303), and is connected to a ground terminal to a first sink resistor (Rsink). A drain terminal of transistor (M2) is directly connected to a drain terminal of transistor (M4) and to the differential voltage amplifier (303), and is connected to a ground terminal to a second sink resistor (Rsink). An output terminal of the differential voltage amplifier (303) is connected to a resistive voltage divider. Source terminals of the transistors (M1, M2) are directly connected together and to a first bias current source (301) without a degeneration resistor, and source terminals of the transistors (M3, M4) are directly connected together and to a second bias current source (302) without a degeneration resistor. The invention also relates to a sensing system comprising a piezoresistive N&MEMS sensor and a monolithically-integrated differential readout circuit comprising said amplifier.