Capacitive Pressure Sensor Sampling Against Time-Varying Parasitics
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Solution Overview
Problem
Electronic circuits implementing sensors face performance degradation due to time-varying parasitic capacitances, such as those caused by water droplets on capacitive pressure sensors, which existing technologies have not effectively mitigated.
Innovation Solution
A sensor system comprising a sense capacitor with a variable sense capacitance and a readout integrated circuit using a MASH modulator and auto-zeroing technique to generate ADC output signals, which includes an offset capacitor charged or discharged out of phase with the sense capacitor, effectively reducing the impact of time-varying parasitic capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sensor circuits are used, then the sensor can detect pressure changes, but time-varying parasitic capacitances (e.g., from water droplets) degrade measurement accuracy
Solution Approach 1:
The patent applies auto-zeroing techniques that sample and store the parasitic capacitance value during a calibration phase, then subtract this stored parasitic value from subsequent measurements. This converts the harmful parasitic capacitance effect into a correctable offset, effectively eliminating its impact on measurement accuracy.
Solution Approach 2:
The patent implements differential measurement modes that switch between measuring the sense capacitor in isolation versus in combination with reference capacitors. By changing the measurement parameter configuration and taking differential differences, the time-varying parasitic capacitances appear as common-mode errors that cancel out in the final measurement.
2Measurement precision
If parasitic compensation techniques are implemented, then measurement accuracy improves, but circuit complexity increases
Solution Approach 1:
The patent combines multiple functions into the same hardware blocks: the sense amplifier performs both signal amplification and parasitic compensation, the MASH modulator handles both modulation and digital filtering, and the capacitor array serves both as signal storage and as reference elements for differential measurements. This integration avoids the need for separate compensation circuits.
Solution Approach 2:
The reference capacitor array serves multiple purposes: it provides reference capacitance values for differential measurement, enables auto-zeroing calibration, and acts as compensation elements for parasitic effects. This multi-functionality reduces the need for dedicated parasitic compensation hardware.
3Speed
If sampling rate is increased to capture fast-changing signals, then signal fidelity improves, but the impact of low-frequency parasitic variations increases
Solution Approach 1:
The patent implements periodic calibration cycles where the auto-zeroing function samples and stores parasitic capacitance values at regular intervals. Between calibration cycles, the stored parasitic values are used to compensate measurements. This periodic action effectively tracks and compensates for low-frequency parasitic variations even at high sampling rates.
Solution Approach 2:
The MASH modulator implements feedback mechanisms where previous measurement results and calibration data are fed back to adjust and compensate current measurements. This feedback loop continuously corrects for parasitic capacitance effects, maintaining accuracy despite high sampling rates and varying environmental conditions.
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 solution significantly reduces the negative impacts of time-varying parasitic capacitances, maintaining accurate pressure measurements by mitigating errors caused by water droplets and other low-frequency impairments, ensuring robust performance of the sensor system.
Implementation Method 1
a sensor system comprising a sense capacitor with a variable sense capacitance and a readout integrated circuit using a MASH modulator and auto-zeroing technique to generate ADC output signals, which includes an offset capacitor operatively charged or discharged out of phase with the sense capacitor
Data Source
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AI summary
Methods and devices to mitigate time varying impairments in sensors are described. The application of such methods and devices to pressure sensors facing time varying parasitic capacitances due to water droplets is detailed. Benefits of auto-zeroing technique as adopted in disclosed devices is also described.