Capacitive Sensor Feedback Circuit to Eliminate Spring Softening
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Solution Overview
Problem
Conventional electromechanical sensors are susceptible to changes in sensitivity due to die stress, assembly variations, and operating conditions, leading to a 'spring softening' effect that alters the resonant frequency and gain of the sensor, which is exacerbated by charge-to-voltage architectures maintaining constant voltage across capacitive sense elements.
Innovation Solution
The application of a positive feedback voltage using a voltage-to-voltage converter, coupled via a defined feedback capacitance to maintain a constant charge at the sense electrode, effectively reducing the sensitivity of the sensor to mechanical-to-electrical gain variations and eliminating the spring softening effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a charge-to-voltage (C2V) architecture is used to maintain constant voltage across the sense gap, then the voltage stability is improved, but the spring softening effect is worsened
Solution Approach 1:
The patent implements a feedback mechanism where the output voltage from the voltage-to-voltage converter is fed back to the sense electrode through a feedback capacitor. This feedback loop actively compensates for charge variations, maintaining constant charge on the sense electrode while allowing voltage to adjust dynamically, thereby eliminating spring softening without sacrificing voltage stability
Solution Approach 2:
The patent transitions from maintaining constant voltage (C2V architecture) to maintaining constant charge through a voltage-to-voltage converter with feedback. This parameter change from voltage control to charge control fundamentally resolves the spring softening issue while preserving the necessary voltage stability for sensor operation
2Device complexity
If conventional sensor technologies are used, then the device complexity is reduced, but the sensitivity changes due to die stress and assembly variations are worsened
Solution Approach 1:
By implementing a feedback capacitor that connects the converter output to the sense electrode, the system automatically compensates for sensitivity changes caused by die stress and assembly variations. This feedback mechanism maintains constant charge, thereby stabilizing the mechanical-to-electrical gain without significantly increasing device complexity
Solution Approach 2:
The voltage-to-voltage converter with feedback capacitor creates a self-regulating system that automatically adjusts to maintain constant charge on the sense electrode. This self-service mechanism compensates for environmental and manufacturing variations without requiring external calibration or complex control circuits
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
This approach significantly minimizes the sensitivity changes of the sensor, reducing the spring softening effect by maintaining a constant charge, thereby stabilizing the sensor's performance across varying conditions.
Implementation Method 1
applying a positive feedback voltage using a voltage-to-voltage converter, coupled via a defined feedback capacitance to maintain a constant charge at the sense electrode
Implementation Method 2
coupled via a defined feedback capacitance to maintain a constant charge at the sense electrode
Implementation Method 3
reducing the sensitivity of the sensor to mechanical-to-electrical gain variations and eliminating the spring softening effect
Data Source
AI summary
Reducing a spring softening effect on a capacitive sense element of an electromechanical sensor is presented herein. A system, such as a microphone or an accelerometer, comprises an electromechanical sensor and a voltage-to-voltage converter component. The electromechanical sensor comprises a capacitive sense element and a bias voltage component that applies a bias voltage to a sense electrode of the capacitive sense element. The voltage-to-voltage converter component couples a positive feedback voltage to the sense electrode to maintain a constant charge at the sense electrode to facilitate a reduction of charge flow in the electromechanical sensor representing a spring softening effect on the capacitive sense element. In an example, the spring softening effect on the sense element alters a resonant frequency of the sense element and a gain of the sense element. In another example, the charge flow corresponds to a parasitic capacitance that is electrically coupled to the sense electrode.