Capacitive Pressure Cell Calibration With Square-Wave Gain And Offset
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Solution Overview
Problem
Existing capacitive pressure sensors face challenges in achieving efficient offset compensation and gain adjustment due to production tolerances, requiring complex methods like laser trimming, and the relocation of analogue function blocks to microcontrollers necessitates further optimization.
Innovation Solution
A method involving an electronic architecture that uses alternating square-wave signals for signal amplification and offset correction, with gain and offset corrections performed through multiplicative and additive influences on capacitance quotients, utilizing a microcontroller for clock generation and digital potentiometers for amplitude adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If laser trimming is used for offset compensation and gain adjustment, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces the mechanical laser trimming process with an electronic/software-based calibration approach. Fixed voltage values are stored in a memory unit and used to generate square-wave signals for offset and gain correction, eliminating the need for physical laser trimming while achieving the same calibration precision.
Solution Approach 2:
The patent changes the calibration parameters from physical resistance values (adjusted by laser trimming) to electrical voltage parameters (stored in memory and applied via square-wave signals). This allows for more flexible and programmable offset and gain adjustment without modifying the physical structure of the sensor.
2Device complexity
If analogue function blocks are relocated to microcontroller, then device complexity is reduced, but manufacturing precision may deteriorate
Solution Approach 1:
The patent replaces analogue function blocks with digital processing in the microcontroller. The microcontroller generates square-wave signals, stores calibration values in memory, and performs the offset and gain corrections digitally, eliminating the need for separate analogue circuitry while maintaining precision through software-based calibration.
Solution Approach 2:
The microcontroller is designed to perform multiple functions: generating the excitation square-wave signal, storing calibration parameters in memory, performing digital signal processing, and executing offset and gain corrections. This multi-functionality consolidates what would otherwise require separate dedicated analogue circuits.
3Manufacturing precision
If complex calibration methods are used, then manufacturing precision is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent performs the complex calibration work in advance by storing fixed voltage values in a memory unit during manufacturing. These pre-calculated calibration parameters are then automatically applied during operation through simple square-wave signal generation, separating the complex calibration step from the manufacturing process.
Solution Approach 2:
The system performs automatic offset and gain correction using pre-stored calibration values without requiring manual intervention during operation. The microcontroller autonomously generates the correction signals and applies them, making the calibration process self-executing after initial setup.
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 reduces sensitivity to interference, enhances robustness against environmental influences and aging, saves costs and space, and ensures a defined signal-to-noise ratio while allowing adjustments to be made remotely from the pressure measuring cell.
Implementation Method 1
Capacitive pressure sensors, or pressure measuring devices, are used in many areas of industry for pressure measurement. They frequently have a ceramic pressure measuring cell as a transducer for the process pressure
Implementation Method 2
the signal amplification being performed by means of an amplitude adjustment for the internal excitation voltage UE0
Implementation Method 3
the offset compensation being performed by way of a further square-wave signal UOF
Data Source
AI summary
A method for operating a pressure measuring cell of a capacitive pressure sensor. The pressure measuring cell includes a pressure-dependent measuring capacitor and a reference capacitor, with an internal alternating square wave excitation voltage applied. The pressure measured value is obtained from capacitance values of the measuring capacitor and the reference capacitor. The measurement signal is an alternating square-wave signal supplied to an evaluation unit. The alternating square-wave signal is supplied to an amplifier unit where signal amplification is performed by amplitude adjustment for the internal excitation voltage and offset compensation is performed by a further square-wave signal and gain correction is performed by multiplicative influencing of the quotient of the capacitance values of the reference capacitor and the measuring capacitor, and the offset correction is performed by virtue of the square-wave signal being supplied to the amplifier unit and thus being added to the square-wave signal.