Dual-Mode Capacitance Sensing Touch Panel Sensor
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Solution Overview
Problem
Capacitive touch panels face challenges in efficiently detecting touch events due to the presence of sensor and parasitic capacitances, which limit the use of larger gain circuits and result in inefficient analog to digital converter (ADC) range, leading to increased component size and cost, and reduced measurement resolution.
Innovation Solution
A touch panel sensor system that provides mutual-capacitance sensing capabilities during one mode of operation and self-capacitance sensing capabilities during another, utilizing a measuring component with multiple integrators and a selection component to generate drive signals with varying amplitudes, and an offset cancellation module to minimize environmental and sensor capacitances, thereby improving dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensor and parasitic capacitances are present in the touch panel, then the touch panel can detect touch events, but the dynamic range and measurement resolution are reduced
Solution Approach 1:
The patent segments the capacitance measurement into two distinct modes: mutual-capacitance sensing and self-capacitance sensing. By separating these measurement functions and applying different drive signal amplitudes to each mode, the system can optimize measurement resolution for each type of capacitance independently, thereby improving overall measurement precision while managing the complexity of parasitic capacitances.
Solution Approach 2:
The patent changes the amplitude parameter of the drive signal based on the sensing mode. During self-capacitance sensing, a lower amplitude drive signal is used compared to mutual-capacitance sensing. This parameter adjustment allows the system to achieve adequate measurement resolution while reducing the impact of parasitic capacitances, thereby improving measurement precision without requiring complete elimination of parasitic elements.
2Measurement precision
If larger gain circuits are used to improve signal detection, then measurement sensitivity increases, but component size and cost increase
Solution Approach 1:
The patent employs dynamic adjustment of drive signal amplitude based on the sensing mode. By making the drive signal amplitude variable rather than fixed, the system achieves high measurement sensitivity when needed while using lower amplitudes during self-capacitance sensing, thereby reducing the need for large gain circuits and associated component size.
Solution Approach 2:
The system changes the drive signal amplitude parameter according to the sensing mode requirements. This parameter adaptation allows the system to achieve adequate signal detection sensitivity without consistently using high-amplitude signals that would require larger gain circuits, thus reducing component size and cost while maintaining measurement precision when necessary.
3Adaptability or versatility
If ADC range is increased to handle capacitance variations, then measurement capability improves, but component cost and complexity increase
Solution Approach 1:
The patent dynamically adapts the drive signal amplitude to match the specific measurement requirements of each sensing mode. This dynamic adjustment ensures that the ADC operates within an optimized range for each mode, improving measurement capability without requiring the ADC to handle the full spectrum of capacitance variations with maximum range, thereby reducing component complexity and cost.
Solution Approach 2:
By changing the drive signal amplitude parameter based on sensing mode, the system optimizes the capacitance measurement range for each specific measurement type. This parameter adaptation allows the use of ADCs with more moderate range requirements, as the system adjusts the input signal to match the ADC's optimal operating range, thereby improving measurement capability while reducing ADC complexity and cost.
4Measurement precision
If mutual-capacitance sensing mode is used, then touch detection accuracy improves, but drive signal amplitude requirements increase
Solution Approach 1:
The patent implements dynamic switching between two drive signal amplitude levels based on the sensing mode. During mutual-capacitance sensing, a higher amplitude is used to achieve superior touch detection accuracy, while during self-capacitance sensing, a lower amplitude suffices. This dynamic adaptation optimizes power consumption by applying high power only when the enhanced accuracy is actually needed.
Solution Approach 2:
The system changes the drive signal amplitude parameter according to the selected sensing mode. This parameter adjustment allows the system to achieve high touch detection accuracy during mutual-capacitance sensing when necessary, while reducing power consumption during self-capacitance sensing where lower amplitude is adequate, thereby balancing measurement precision with power efficiency.
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 enhances the dynamic range and resolution of touch panel sensors by effectively distinguishing between touch event capacitance and parasitic capacitances, allowing for smaller integrating capacitors and improved signal-to-noise ratios, while maintaining efficient component usage and cost-effectiveness.
Implementation Method 1
Capacitive touch panels are often used with touch screen devices. A capacitive touch panel generally includes an insulator, such as glass, coated with a transparent conductor, such as indium tin oxide (ITO). As the human body is also an electrical conductor, touching the surface of the panel results in a distortion of the panel's electrostatic field, measurable as a change in capacitance.
Data Source
AI summary
A touch panel sensor system configured to measure mutual-capacitance and self-capacitance is disclosed. The touch panel sensor system includes a sensor configured to detect a change in capacitance associated with a touch event upon a touch panel and a measuring component. The measuring component is configured to detect mutual-capacitance during the first mode of operation and to detect self-capacitance during the second mode of operation. The system also includes a selection component that is configured to receive a selection signal to cause selection of the mode of operation. The system also includes a driver component coupled to the selection component and configured to generate a drive signal, which is furnished to the sensor during the first mode of operation and furnished to the measuring module during the second mode of operation. The amplitude characteristic of the drive signal may have differing values for the first and second modes of operation.