Capacitive Pressure Sensor Non-Linearity Correction
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Solution Overview
Problem
Automotive pressure sensors exhibit significant non-linearity errors due to their capacitive-based parallel plate configuration, leading to inaccuracies in pressure measurement.
Innovation Solution
Incorporating a linear mapping function of 1/CX value in the integrated circuit of the pressure sensor, which reduces non-linearity errors and enables two-point calibration of the relationship between pressure and capacitance, using a pair of parallel electrodes, ceramic plates, and rigid glass seals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a capacitive-based parallel plate configuration is used in the pressure sensor, then the sensor structure is simple and manufacturing is easy, but significant non-linearity errors occur in capacitance to voltage conversion
Solution Approach 1:
The patent changes the mathematical parameter used for conversion from direct capacitance (C) to the inverse of capacitance (1/C). This parameter transformation linearizes the relationship between pressure and output signal, eliminating non-linearity errors while maintaining the simple capacitive parallel plate structure. The IC now processes 1/C values instead of C values, fundamentally changing the conversion approach.
2Ease of operation
If traditional capacitance to voltage conversion is used, then the conversion process is straightforward, but non-linearity errors significantly degrade measurement accuracy
Solution Approach 1:
The conversion process now operates on 1/C values instead of C values. This parameter change transforms the non-linear capacitance-pressure relationship into a linear relationship, making the conversion operation as straightforward as before but with significantly improved measurement precision. The IC executes linear mapping functions on 1/C values to produce accurate pressure readings.
3Measurement precision
If multiple calibration points are used to correct non-linearity, then measurement accuracy improves, but device complexity and calibration time increase
Solution Approach 1:
By changing the conversion parameter from C to 1/C, the patent achieves linearization that requires only two calibration points (zero span and full span) instead of multiple points. This dramatically reduces calibration complexity and time while maintaining high measurement precision across the entire pressure range.
Solution Approach 2:
The patent performs preliminary linearization by converting to 1/C values before final pressure calculation. This preliminary action eliminates the need for complex multi-point calibration procedures, as the linear relationship is established through the mathematical transformation itself rather than through extensive calibration data collection and polynomial fitting.
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 effectively minimizes non-linearity errors associated with capacitance conversion, allowing for accurate two-point calibration and reducing the need for additional calibration points, thereby enhancing measurement precision and accuracy.
Implementation Method 1
an automotive pressure sensor (APT) is a capacitive-based sensor that provides a linear voltage output directly proportional to applied pressure
Implementation Method 2
Because of the construction of a capacitive pressure element, and particularly a parallel plate configuration
Data Source
AI summary
Methods and apparatus for reduction of non-linearity errors in automotive pressure sensors. A pressure sensor includes a pressure sensing element including a pair of parallel electrodes, a pair of ceramic plates, rigid glass seals and a connection between the pair of parallel electrodes and an integrated circuit (IC). The IC executes a linear mapping function of a 1/CX value after a CX value is captured from the pressure sensing element, C representing a capacitance, the linear mapping function reducing a non-linearity error to enable two point calibration of a relationship between pressure and capacitance.