Capacitive Measurement Circuit Parasitic Capacitance Compensation
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Solution Overview
Problem
Current touch sensors, particularly capacitive touch screens, face challenges in accurately detecting the presence and location of touches or proximity due to variations in parasitic capacitance across non-uniform sense lines, which can lead to inaccurate touch detection and processing.
Innovation Solution
The implementation of a measurement circuit with compensation buffers and current summer/divider circuits that adjust and calculate average capacitance to compensate for parasitic capacitance differences, ensuring accurate detection and processing of touch inputs by normalizing capacitance signals across sense lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If capacitive touch sensors use non-uniform sense lines for touch detection, then the sensor can cover larger areas and support multiple touch points, but parasitic capacitance variations cause inaccurate touch detection and processing
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the drive signal parameters (frequency, amplitude, or phase) based on the detected touch location and parasitic capacitance variations. The controller modifies these parameters to compensate for non-uniform parasitic capacitance distribution across different sense lines, thereby maintaining accurate touch detection across the entire sensor area despite variations in parasitic effects.
Solution Approach 2:
The patent implements feedback mechanisms where the controller continuously monitors the capacitance changes from multiple sense lines and uses this information to adjust the drive signals. The system processes the raw capacitance data, identifies parasitic capacitance variations, and modifies subsequent measurements and drive signals to compensate for these variations, ensuring consistent touch detection accuracy across non-uniform sense line configurations.
2Reliability
If the sensor applies drive signals to sense lines to detect capacitance changes, then touch detection is enabled, but parasitic capacitance introduces errors in the measurement
Solution Approach 1:
The patent introduces intermediary elements including reference capacitance circuits and compensation networks that act as mediators between the sense lines and the measurement system. These intermediaries provide reference values and compensation signals that help filter out parasitic capacitance effects from the actual touch-induced capacitance changes, enabling reliable measurement despite the presence of parasitic interference.
Solution Approach 2:
The patent extracts and separates parasitic capacitance effects from the total measured capacitance signal. By using multiple sense lines with known parasitic characteristics and reference measurements, the system isolates and removes the parasitic capacitance component from the measurement, leaving only the genuine touch-induced capacitance changes for accurate processing.
3Productivity
If the sensor uses multiple sense lines to improve detection coverage, then the sensor can detect more touch points simultaneously, but the complexity of compensating for parasitic capacitance variations increases
Solution Approach 1:
The patent segments the touch sensor into multiple independent sense line channels, each with its own dedicated processing path. This segmentation allows the system to handle parasitic capacitance compensation for each sense line individually using standardized compensation circuits and algorithms, making the overall complex task of multi-line compensation manageable through modular, parallel processing of each segment.
Solution Approach 2:
The patent employs universal compensation circuits and algorithms that can be applied across all sense lines regardless of their specific parasitic characteristics. The same basic compensation mechanism (reference capacitance circuits, signal processing algorithms) serves multiple sense lines, reducing the overall system complexity compared to having separate compensation mechanisms for each line while still achieving accurate compensation across diverse sense line configurations.
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 solution enhances the accuracy of touch detection and processing by minimizing the impact of parasitic capacitance variations, leading to improved reliability and precision in determining the presence and location of touches on capacitive touch sensors.
Implementation Method 1
When an object touches or comes within proximity of the surface of the capacitive touch screen, a change in capacitance may occur within the touch screen at the location of the touch or proximity
Data Source
AI summary
In one embodiment, a method for determining the location of a touch on a touch sensor includes receiving input signals in response to a touch proximate to a location on the touch sensor. Each input signal may have a total capacitance that includes a first capacitance associated with the touch and a second capacitance that is parasitic capacitance. The parasitic capacitance of one or more of the input signals may be adjusted to result in the second capacitance of each of the input signals being substantially equal. An average capacitance of the adjusted input signals may be calculated. The location of the touch on the touch sensor may then be determined based on a comparison of the total capacitance of each of the input signals and the average capacitance of the input signals.