ADC Sampling Capacitor Touch Sensing Without External Oscillators
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Solution Overview
Problem
Existing capacitive touch sensing technologies face challenges in detecting small changes in capacitance due to the need for stable reference time bases, non-ideal behavior with temperature and voltage changes, electrical noise, and sensitivity to external noise, particularly in relaxation and LC oscillators, which require costly and complex components.
Innovation Solution
A method utilizing an internal sampling capacitor of an ADC, charged to a reference voltage, transfers charge to an external capacitor, allowing for capacitance determination without requiring external oscillators or high stability time bases, minimizing noise pickup by maintaining low source impedance and using over-sampling for increased resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If a relaxation oscillator is used to detect capacitance changes, then capacitance detection capability is achieved, but measurement stability deteriorates due to insufficient reference time base stability
Solution Approach 1:
The patent replaces the mechanical relaxation oscillator system with an electronic charge transfer system using an ADC's internal sampling capacitor. This substitution eliminates the need for external oscillators and resonators, achieving both capacitance detection capability and measurement stability through digital conversion and processing.
Solution Approach 2:
The invention utilizes the ADC's internal sampling capacitor and reference voltage, which are already present in the system, to perform capacitance measurement. This self-service approach eliminates the need for external components and ensures stable measurements using existing stable internal resources.
2Difficulty of detecting and measuring
If a relaxation oscillator is used for capacitance detection, then capacitance measurement function is achieved, but device complexity increases due to required resonator or crystal components
Solution Approach 1:
The patent makes the ADC's internal sampling capacitor serve dual purposes: its original function in the ADC conversion process and a new function as the measurement capacitor for capacitance detection. This multi-functionality eliminates the need for separate external capacitors and oscillators, reducing device complexity while maintaining measurement capability.
Solution Approach 2:
The system uses its own internal ADC resources (sampling capacitor, reference voltage, ADC converter) to perform capacitance measurement, eliminating the need for external specialized components and simplifying the overall device architecture.
3Object-generated harmful factors
If the sensor capacitor and voltage amplitude are reduced to minimize noise, then electrical noise is reduced, but measurement precision deteriorates for detecting small capacitance changes
Solution Approach 1:
The patent replaces the analog oscillator-based measurement system with a digital charge transfer system. This substitution allows for precise measurement of small capacitance changes through digital conversion and processing, achieving both low noise and high precision simultaneously.
Solution Approach 2:
The system uses the ADC to convert the voltage signal to digital form, enabling precise measurement and processing. The digital domain provides inherent noise immunity and allows for sophisticated signal processing algorithms to detect small capacitance changes with high precision while maintaining low noise levels.
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 effectively determines small changes in capacitance with improved noise immunity and stability over temperature and voltage, reducing component costs and complexity, while minimizing electromagnetic interference.
Implementation Method 1
charging to a reference voltage an internal sampling capacitor of an analog-to-digital converter (ADC), then transferring some of the voltage charge on the internal sampling capacitor to an external capacitor
Data Source
Figure 1(a)~1(c)
Figure 2(a)~2(d)
Figure 3(a)~3(d)
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.