Capacitance-to-Digital Converter With Scaled Reference Charging
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Solution Overview
Problem
Conventional capacitance to digital converters require reference capacitors with larger capacitance values than the sensor, limiting flexibility in measuring large capacitances and necessitating external, large-capacitance components.
Innovation Solution
The concept involves downscaled reference 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 various applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If reference capacitors are used with capacitance values equal or larger than the sensor capacitance, then the measurement range is limited to small capacitance values, but using larger reference capacitors increases device size and complexity
Solution Approach 1:
The patent changes the voltage parameter applied to the sensor capacitance during measurement phases. By applying different voltages (first voltage in sampling phase, second voltage in holding phase) to the sensor capacitance, the system can measure a wider range of capacitance values without requiring large reference capacitors. The charge stored on the sensor capacitance is scaled according to the voltage ratio, enabling measurement of both small and large capacitance values with the same reference capacitor.
2Adaptability or versatility
If large capacitance values are measured, then reference capacitors must have large capacitance values, but this requires external circuit elements and reduces integration possibilities
Solution Approach 1:
The patent enables integration by changing the voltage parameter instead of the capacitance parameter. By applying scaled voltages to the sensor capacitance during different phases, the system can measure large capacitance values while keeping reference capacitors small and integrable. The charge relationship Q=C×V allows the same reference capacitor to effectively measure a wide range of sensor capacitance values through voltage scaling.
3Adaptability or versatility
If reference capacitors are provided externally, then large capacitance measurements are possible, but this increases device complexity and cost
Solution Approach 1:
The patent merges the reference capacitor into the integrated circuit with the sensor interface, eliminating the need for external large-capacitance components. By combining the reference capacitor with the sensor capacitance in a shared circuit architecture and using phase-based voltage scaling, the system achieves both integration and wide measurement range capability within a single compact device.
4Ease of operation
If the same voltage is used for charging sensor and reference capacitors, then the measurement is simple, but the measurement range is limited by the reference capacitor value
Solution Approach 1:
The patent uses periodic action by switching between different voltage phases (sampling phase with first voltage, holding phase with second voltage) applied to the sensor capacitance. This periodic voltage variation allows the system to measure a wide range of capacitance values while maintaining a simple charge-compare measurement mechanism. The sequential phase operation preserves measurement simplicity while extending the effective measurement range.
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 solution suitable for a wide range of capacitive sensors by scaling the charge stored on the sensor capacitance, thus enhancing measurement capabilities without increasing costs.
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
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AI summary
A capacitance to digital converter, CDC, has a first and a second reference terminal (T1, T2) for receiving first and second reference voltages (VREFP, VREFN), a reference block (CREF) comprising one or more reference charge stores and being coupled to the first and second reference terminals (T1, T2) via a first switching block (SWB1), a scaling block (SCB) for providing at third and fourth reference terminals (T3, T4) downscaled voltages (SVREFP, SVREFN) from the first and second reference voltages (VREFP, VREFN) depending on a scaling factor, first and second measurement terminals (M1, M2) for connecting a capacitive sensor element (CS), the first measurement terminal (M1) being coupled to the third and fourth reference terminals (T3, T4) via a second switching block (SWB2), and a processing block (PROC) coupled to the reference block (CREF) and to the second measurement terminal (M2) and being configured to determine a digital output signal based on a charge distribution between the sensor element (CS) and the reference block and based on the scaling factor, the output signal representing a capacitance value of the sensor element (CS).