Capacitance-to-Digital Converter With Voltage Scaling for Wider Range
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Solution Overview
Problem
Conventional capacitance to digital converters require reference capacitors with larger capacitance values than the sensor, limiting their flexibility in measuring large capacitances and necessitating external, large-capacitance components.
Innovation Solution
The proposed solution involves downscaled voltages for charging both the capacitive sensor and reference capacitors, allowing for ratiometric processing independent of actual reference voltage values, enabling smaller reference capacitances and integrating them into an integrated circuit, with a scaling factor that can be adjusted for different applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference capacitors are used with capacitance values equal to or larger than the sensor capacitance, then the measurement range is limited to small capacitance values, but the device complexity and external component requirements are reduced
Solution Approach 1:
The patent changes the voltage parameter used for charging the sensor capacitor, applying a downscaled voltage instead of the full reference voltage. This allows the reference capacitors to have smaller capacitance values while still accurately measuring larger sensor capacitances, thereby expanding the measurement range without requiring large external reference capacitors
Solution Approach 2:
The patent introduces a voltage scaling dimension by applying different voltage levels to the sensor capacitor compared to the reference capacitors. By charging the sensor with a downscaled voltage and compensating through ratiometric processing with a known scaling factor, the system can measure larger capacitance values using smaller reference capacitors
2Measurement precision
If large capacitance values are measured, then the measurement range is expanded, but reference capacitors with large capacitance values are required
Solution Approach 1:
The patent changes the voltage parameter applied to the sensor capacitor, using a downscaled reference voltage for charging the sensor instead of the full reference voltage. This parameter change allows the use of smaller reference capacitance values while maintaining the ability to measure larger sensor capacitance values, effectively decoupling the reference capacitance size from the measurement range
3Device complexity
If reference capacitors are integrated into an integrated circuit, then device complexity is reduced, but the measurement of large capacitances becomes difficult
Solution Approach 1:
The patent applies a downscaled voltage to the sensor capacitor during measurement, which allows integrated reference capacitors with small capacitance values to accurately measure larger sensor capacitances. This voltage scaling approach enables full integration of the CDC circuit while expanding the measurable capacitance range beyond what would be possible with conventional equal-capacitance reference capacitors
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 expands the measurement range of capacitive sensors, reduces the need for large external capacitors, and allows for a cost-effective, flexible CDC that can handle a wide range of capacitance values without increasing device cost.
Implementation Method 1
A scaling block provides at a third and a fourth reference terminal downscaled voltages from the first and second reference voltages depending on a scaling factor
Implementation Method 2
the charge that is stored on a capacitance depends on both the capacitance value and the voltage, with which the capacitance is charged
Data Source
AI summary
A capacitance to digital converter, CDC, has a first and a second reference terminal for receiving first and second reference voltages, a reference block comprising one or more reference charge stores and being coupled to the first and second reference terminals via a first switching block, a scaling block for providing at third and fourth reference terminals downscaled voltages from the first and second reference voltages depending on a scaling factor, first and second measurement terminals for connecting a capacitive sensor element, the first measurement terminal being coupled to the third and fourth reference terminals via a second switching block, and a processing block coupled to the reference block and to the second measurement terminal and being configured to determine a digital output signal based on a charge distribution between the sensor element and the reference block and based on the scaling factor, the output signal representing a capacitance value of the sensor element.