Capacitive Sensor Calibration via Independent Offset and Sensitivity Adjustment
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Solution Overview
Problem
Capacitive sensing devices often deviate from design specifications due to manufacturing and assembly errors, leading to capacitance and sensitivity variations that require effective calibration to rectify zero-offset and sensitivity errors.
Innovation Solution
A calibration apparatus and method using a calibration capacitor device, integration circuit with latch function, and switching circuits to transform sensitivity and zero-offset calibration parameters into analog signals, allowing independent adjustment of these parameters to match specifications, utilizing two independent digital calibration codes to control voltages on capacitive device electroplates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods using dependent digital codes and code mirrors are used, then zero-offset and sensitivity can be calibrated, but the calibration complexity and margin tolerance increase
Solution Approach 1:
The patent divides the calibration process into two independent parts: zero-offset calibration and sensitivity calibration. Each part uses separate digital codes (first digital code for zero-offset, second digital code for sensitivity) rather than dependent codes, allowing independent adjustment and reducing the complexity of the calibration circuit.
Solution Approach 2:
The patent changes the calibration parameters from dependent digital codes to independent digital codes, and from voltage-based calibration to capacitance-based calibration using a calibration capacitor device. This parameter change simplifies the calibration circuit and reduces margin tolerance while maintaining high precision.
2Productivity
If manufacturing and assembly processes are used, then capacitive sensing devices are produced, but capacitance and sensitivity deviations occur
Solution Approach 1:
The patent implements a self-calibration mechanism where the capacitive sensing device automatically adjusts its own zero-offset and sensitivity parameters through the calibration circuit. The device uses its own sensing capacitors and calibration capacitor to perform calibration without requiring external intervention, ensuring consistent precision across mass production.
Solution Approach 2:
The patent compensates for manufacturing deviations by dynamically adjusting calibration parameters (capacitance values) rather than relying on precise manufacturing. The calibration capacitor device allows post-manufacturing adjustment of capacitance parameters to correct deviations caused by non-ideal manufacturing and assembly processes.
3Measurement precision
If calibration circuits adjust voltages on capacitor plates, then zero-offset and sensitivity errors are rectified, but the calibration process becomes complex
Solution Approach 1:
The patent replaces the traditional voltage-based calibration mechanism with a capacitance-based calibration mechanism. Instead of adjusting voltages on capacitor plates through complex circuitry, the system adjusts the capacitance value of the calibration capacitor device, simplifying the calibration process while maintaining high precision for zero-offset and sensitivity correction.
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 enables precise calibration of capacitive sensing devices by independently adjusting zero-offset and sensitivity, reducing calibration complexity and margin tolerance, and allowing for high-precision voltage output while facilitating self-test modes.
Implementation Method 1
a calibration capacitor device, an integration circuit with latch function
Data Source
AI summary
A calibration apparatus and method for a capacitive sensing device, in which a calibration capacitor device connects to the capacitive sensing device which is connected to an integration circuit that generates a voltage output and a latch output, a transforming circuit transforms a sensitivity calibration parameter into a pair of corresponding analog signal outputs, and an offset calibration parameter into a corresponding analog signal output, at least two first switches between the pair of corresponding analog signal outputs and a fixed potential according to system clock's levels, and at least a third switch switches between the corresponding analog signal output and another fixed potential according to the system clock's levels. The apparatus determines the switch between the pair of signal outputs according to the latch output.