ADC Sampling Capacitor Charge Transfer for Precise Touch Sensing
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Solution Overview
Problem
Existing capacitive touch sensing technologies face challenges in detecting small changes in capacitance due to instability in reference time bases, non-ideal behavior of relaxation oscillators, electrical noise, and sensitivity to external noise, which require costly and complex components.
Innovation Solution
A method utilizing an internal sampling capacitor of an analog-to-digital converter (ADC) is charged to a reference voltage and then coupled with an external capacitor, allowing for the measurement of voltage differences to determine capacitance changes, minimizing noise pickup and stability issues without the need for external oscillators or high-stability time bases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a relaxation oscillator is used to detect capacitance changes, then capacitance detection can be achieved, but the reference time base requires high stability components (resonator or crystal) which increases cost and complexity
Solution Approach 1:
The patent extracts the time base function from a separate oscillator circuit and integrates it into the ADC's internal sampling capacitor operation. The ADC's clock signal serves as the time base, eliminating the need for external resonators or crystals while maintaining measurement precision.
Solution Approach 2:
The patent makes the ADC's sampling capacitor serve dual functions: its primary function for analog-to-digital conversion and a secondary function as the sensor capacitor for capacitance measurement. This eliminates the need for separate dedicated oscillator components.
2Object-affected harmful factors
If an LC oscillator is used for capacitance detection, then fewer harmonics are generated, but the component cost increases due to required inductor and more complicated oscillator circuit
Solution Approach 1:
The patent removes the LC oscillator circuit entirely and uses the ADC's internal sampling capacitor with its existing clock signal. This eliminates inductors and complex oscillator circuits while maintaining low EMI characteristics through the inherent simplicity of the RC-based timing.
3Measurement precision
If external capacitors are used in charge transfer techniques, then capacitance measurement can be performed, but additional external components are required which increases device complexity
Solution Approach 1:
The patent makes the ADC's internal sampling capacitor serve as both the conversion capacitor and the sensor capacitor for measurement. This eliminates the need for external capacitors while maintaining measurement accuracy through the capacitor's known stable value.
Solution Approach 2:
The ADC's internal resources (sampling capacitor and clock signal) are used to perform the capacitance measurement function, making the system self-sufficient without requiring external components that would increase device complexity.
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 accurate detection of small capacitance changes with improved noise immunity and stability over temperature and voltage, reducing component costs and complexity.
Implementation Method 1
charging from a voltage reference an internal capacitor in an integrated circuit device to a first voltage, wherein the internal capacitor has a known capacitance
Implementation Method 2
coupling the internal capacitor to the external capacitor with a second switch in the integrated circuit device so that some of the charge on the internal capacitor is transferred to the external capacitor
Implementation Method 3
measuring a second voltage charge on the internal capacitor with the ADC in the integrated circuit device
Data Source
AI summary
An internal sampling capacitor of an analog-to-digital converter (ADC) in a digital device is charged to a reference voltage, then some of the voltage charge on the internal sampling capacitor is transferred to an external unknown capacitor through a low resistance switch internal to the digital device. After the charge transfer has stabilized, the voltage charge remaining on the internal sampling capacitor is measured. The difference between the known reference voltage and the voltage remaining on the internal sampling capacitor is used to determine the capacitance value of the external capacitor. Alternatively, the external capacitor may be charged to a reference voltage then the external capacitor is coupled to the internal sampling capacitor, e.g., having no charge or a known charge on it, and the resulting voltage charge on the internal sampling capacitor is measured and used for determining the capacitance value of the external capacitor.