Single Amplifier Capacitive Transducer for Linearity
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Solution Overview
Problem
Self-balanced capacitive bridges face non-linearity issues due to feedthrough capacitance and residual electrostatic forces, which are difficult to address without significant additional circuitry, such as summing amplifiers, that occupy substantial chip area.
Innovation Solution
A capacitive transducer system that includes a neutralization capacitor to cancel feedthrough and parasitic capacitances, and uses a single amplifier to eliminate residual electrostatic forces, reducing non-linearity without requiring extensive additional circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If summing amplifiers are added to cancel residual electrostatic forces, then measurement precision is improved, but device complexity increases and chip area occupied increases
Solution Approach 1:
The patent combines the functions of multiple amplifiers into a single amplifier by integrating the electrostatic force cancellation function with the main signal amplification function. The single amplifier performs both tasks simultaneously, eliminating the need for separate summing amplifiers and reducing circuit complexity while maintaining measurement precision.
Solution Approach 2:
The single amplifier is designed to perform multiple functions: it amplifies the differential signal from the capacitive bridge and simultaneously cancels residual electrostatic forces. This multi-functional approach replaces what would traditionally require separate dedicated circuits, reducing overall device complexity.
2Measurement precision
If summing amplifiers are added to cancel residual electrostatic forces, then measurement precision is improved, but area of stationary object increases
Solution Approach 1:
The patent merges the electrostatic force cancellation circuitry with the main amplifier circuit, eliminating the need for separate summing amplifiers. This integration significantly reduces the chip area required while maintaining the ability to cancel residual electrostatic forces and improve measurement precision.
Solution Approach 2:
The patent extracts and eliminates the redundant summing amplifier components from the traditional design, keeping only the essential single amplifier that performs both signal amplification and electrostatic force cancellation, thereby reducing chip area.
3Measurement precision
If neutralization capacitor is used to cancel feedthrough capacitance, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The neutralization capacitor acts as an intermediary element that cancels the effect of feedthrough capacitance. By introducing this capacitor in parallel with the signal path, the circuit compensates for parasitic effects without requiring complex additional circuitry, thus improving measurement precision with minimal increase in device complexity.
4Device complexity
If traditional capacitive bridge is used, then device complexity is reduced, but measurement precision deteriorates due to non-linearity
Solution Approach 1:
The patent implements feedback through the single amplifier that reads the differential output and simultaneously applies corrective feedback to cancel residual electrostatic forces. This feedback mechanism enables the simple capacitive bridge structure to achieve high measurement precision by dynamically compensating for non-linearities.
Solution Approach 2:
The patent changes the electrical parameters (voltages and currents) through the single amplifier to actively cancel residual electrostatic forces. By dynamically adjusting these parameters based on the differential signal, the system maintains high measurement precision while keeping the overall circuit structure simple.
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 system effectively reduces or eliminates non-linearity due to feedthrough and parasitic capacitances and residual electrostatic forces, achieving improved performance with minimal additional chip area, using a single amplifier and on-chip neutralization.
Implementation Method 1
A capacitive transducer system includes a neutralization capacitor to cancel feedthrough and parasitic capacitances
Implementation Method 2
capacitive transducers produce a change of capacitance, corresponding to the magnitude of the measured input signal. Readout circuits for capacitive transducers transform the capacitance change produced by the transducer to an electrical signal
Implementation Method 3
residual electrostatic forces contributed by sensor circuitry
Data Source
Figure 1~2
Figure 3~4
Figure 5A~6
AI summary
Capacitive transducer systems are disclosed that reduce nonlinearities due to feedthrough capacitances or residual electrostatic forces. The systems can include a core with a first input coupled to a first variable capacitor, a second input coupled to a second variable capacitor, and a core output coupled to a common node; an amplifier with input switchably coupled to common node and an output; a feedback path switchably coupling amplifier output to common node; and a main clock with first and second phases, that controls switches coupling system components. When clock is in first phase, first core input is coupled to reference voltage, second core input is coupled to negative reference voltage, and common node is coupled to amplifier output. When clock is in second phase, core inputs are grounded, and common node is coupled to amplifier input. The system can have single amplifier. Neutralization capacitor can cancel feedthrough and parasitic capacitances.