Variable Sample-and-Hold Capacitor for Noisy Capacitive Touch ADCs
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Solution Overview
Problem
Conventional capacitive touch systems face limitations in resolution, especially in high noise environments with high bulk capacitance, due to the inherent capacitance of sensors and system parasitic capacitances, which affects their accuracy in detecting touch events.
Innovation Solution
A microcontroller system with an adjustable sample-and-hold capacitance that can be programmably enhanced to match the sensor capacitance, using capacitive voltage division (CVD) for improved resolution, and a control unit to automatically measure and adjust capacitances for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional fixed sample-and-hold capacitor is used in the ADC, then the device complexity is low, but the measurement precision is insufficient in high noise environments with high bulk capacitance
Solution Approach 1:
The patent implements a dynamic sample-and-hold capacitor architecture where the capacitance value can be programmably adjusted through software control. Multiple capacitor banks are switchably connected in parallel to the main sample-and-hold capacitor, allowing the total capacitance to be dynamically adapted to match different sensor capacitance values. This resolves the contradiction by enabling measurement precision improvement through capacitance matching while maintaining relatively simple device complexity through modular capacitor banks and control logic.
Solution Approach 2:
The patent changes the electrical parameter (capacitance value) of the sample-and-hold capacitor to optimize measurement precision. By programmably adjusting the capacitance ratio between the sensor capacitor and sample-and-hold capacitor, the system achieves better resolution in capacitive touch sensing. This parameter change approach allows the system to adapt to different sensing conditions without fundamentally redesigning the ADC architecture.
2Measurement precision
If the sample-and-hold capacitance is increased to match high bulk capacitance sensors, then the measurement precision improves, but the device complexity increases due to additional capacitance adjustment circuitry
Solution Approach 1:
The patent segments the sample-and-hold capacitance into multiple discrete capacitor banks that can be independently controlled. Each capacitor bank can be switchably connected in parallel to the main sample-and-hold capacitor, creating a modular architecture. This segmentation allows precise capacitance matching through selective activation of individual banks, improving measurement precision while keeping device complexity manageable through modular design and incremental capacitance adjustment.
3Measurement precision
If a variable sample-and-hold capacitance is implemented to match sensor capacitance, then the resolution is enhanced, but the ease of operation decreases due to software control requirements
Solution Approach 1:
The patent implements self-service through automated capacitance matching where the microcontroller automatically selects and configures the appropriate capacitor bank combinations based on the connected sensor characteristics. The system performs self-calibration and adaptive optimization without requiring manual intervention, thereby maintaining ease of operation while achieving enhanced resolution through variable capacitance matching.
Solution Approach 2:
The patent employs feedback mechanisms where the system monitors the sensor capacitance characteristics and automatically adjusts the sample-and-hold capacitor configuration to achieve optimal matching. This closed-loop control enables the system to adapt to different sensors and operating conditions automatically, improving resolution while minimizing the operational burden on the user through automated adjustment based on real-time feedback.
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
The system achieves enhanced resolution and noise immunity by matching sample-and-hold capacitance with sensor capacitance, allowing for precise detection of touch events even in challenging environments.
Implementation Method 1
analog-to-digital converter (ADC) with an adjustable sample-and-hold capacitor
Implementation Method 2
One such application utilizes capacitive voltage division (CVD) to evaluate whether a capacitive touch element has been touched or not
Data Source
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Figure 3A
AI summary
An ADC module includes an analog to digital converter coupled with an analog bus, wherein the an analog to digital converter comprises a main sample and hold capacitor; and a plurality of additional sample and hold capacitances which can be programmably coupled in parallel with said main sample and hold capacitance.