Capacitive Pressure Sensor Calibration for Stress Drift Compensation
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Solution Overview
Problem
Pressure sensors face challenges in maintaining accuracy due to mechanical and thermal stress changes during assembly and over time, leading to deviations in pressure readings, which existing calibration methods fail to compensate for effectively.
Innovation Solution
A sensor arrangement utilizing a differential capacitance-to-digital converter design with a variable voltage reference, allowing for the measurement of transducer characteristics during calibration and assembly, and on-chip read-out circuitry to compensate for stress changes and extract membrane compliance and pressure sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive pressure sensor is used, then sensitivity and measurement capability are improved, but the sensor becomes sensitive to mechanical and thermal stress changes that cause accuracy degradation over time
Solution Approach 1:
The patent applies parameter changes by varying the reference voltage to different values (at least two different values with the same sign and different amounts) during testing. This allows the system to measure capacitance at multiple operating points and determine parameters A0 and B0 that characterize the sensor's voltage-dependent behavior, enabling compensation for stress-induced drift.
Solution Approach 2:
The patent implements feedback by using the measured capacitance values at different reference voltages to calculate correction parameters (A0, B0) that are stored and applied during normal operation. The digital circuit continuously compensates for stress effects by adjusting readings based on the pre-determined voltage-dependent characteristics.
2Measurement precision
If calibration is performed using external equipment, then initial accuracy can be achieved, but the system cannot compensate for stress changes occurring during assembly and over the sensor's lifetime
Solution Approach 1:
The patent applies preliminary action by performing the calibration procedure during the manufacturing or assembly phase, before the sensor is deployed. The system determines the voltage-dependent parameters (A0, B0) and stores them in memory during this initial phase, preparing the compensation mechanism in advance so that it can automatically correct for stress effects that will occur during assembly and operation.
Solution Approach 2:
The patent implements self-service by enabling the sensor system to perform its own calibration and compensation without requiring external equipment during operation. The on-chip read-out circuitry and digital circuit automatically measure capacitance, calculate correction parameters, and apply compensation to maintain accuracy throughout the sensor's lifetime.
3Object-affected harmful factors
If on-chip read-out circuitry is integrated, then connection length is reduced and noise is minimized, but device complexity increases
Solution Approach 1:
The patent applies merging by integrating the read-out circuitry, reference voltage generator, capacitance-to-digital converter, and digital processing functions directly onto the same chip as the pressure sensor. This consolidation eliminates external connections, reduces parasitic effects and noise, and enables the sensor to perform self-calibration and compensation functions.
Solution Approach 2:
The patent implements universality by designing the integrated circuit to perform multiple functions: generating reference voltages, measuring capacitance at different voltage levels, converting analog signals to digital, storing calibration parameters in memory, and performing real-time compensation calculations. This multi-functional approach reduces the need for separate external components.
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 enhances the accuracy and reliability of pressure sensor readings by compensating for mechanical and thermal stress changes, improving sensitivity and linearity, and reducing noise, thereby maintaining precise pressure measurements over the lifetime of the sensor.
Implementation Method 1
A pressure sensor typically has a membrane... The membrane is deflected in the case of a pressure difference between the two sides of the membrane. A pressure sensor is often realized as a capacitive pressure sensor. Thus, the deflection of the membrane results in a change of a capacitance value of the pressure sensor.
Implementation Method 2
The reference voltage generator is configured to set a value of the reference voltage as a function of the control signal. At least two different values of the reference voltage have the same sign and different amounts... the distance of a first electrode of the sensor to a second electrode of the pressure sensor can be varied by the at least two different values of the reference voltage.
Data Source
AI summary
In an embodiment a sensor arrangement includes a pressure sensor realized as a capacitive pressure sensor, a capacitance-to-digital converter coupled to the pressure sensor and implemented as a delta-sigma analog-to-digital converter and a reference voltage generator having a control input configured to receive a control signal and an output configured to provide a reference voltage, wherein the output of the reference voltage generator is connected to an input of the capacitance-to-digital converter, wherein the reference voltage generator is configured to set a value of the reference voltage as a function of the control signal, and wherein at least two different values of the reference voltage have the same sign and different amounts.