Capacitive Touch Panel Driver Array Using Segmented Drive Signals
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Solution Overview
Problem
Capacitative touchscreens face challenges in sensing multi-touch inputs on large panels due to reduced measurement time, increased susceptibility to interference, stronger coupling between conductors, and higher power consumption, which existing methods attempt to address by increasing voltage but lead to electromagnetic interference and circuit difficulties.
Innovation Solution
A multi-touch sensing system that estimates touch locations by measuring changes in mutual capacitances between rows and columns using a driver array with overlapping but mathematically independent row drive signals, a receiver array for digital signal processing, and a signal processing system to correlate signals and reject noise, thereby reducing electromagnetic interference and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the panel size is increased to support large displays, then the display area is improved, but the measurement time available for each capacitance decreases and electromagnetic interference increases
Solution Approach 1:
The patent divides the large panel into multiple zones or regions, allowing simultaneous or interleaved measurement of different segments. This segmentation enables the system to handle the increased panel area without proportionally increasing total measurement time, as multiple regions can be measured in parallel or with optimized scanning patterns.
Solution Approach 2:
The patent employs periodic drive signals at optimized frequencies to excite the capacitance elements. By using periodic actions with carefully selected frequencies, the system achieves sufficient measurement resolution within the reduced time window, while the periodic nature allows for synchronized sampling across the large panel area.
2Measurement precision
If higher voltages are used to compensate for reduced measurement time, then the signal strength is improved, but electromagnetic interference and circuit difficulties increase
Solution Approach 1:
The patent changes the voltage parameters by using lower drive voltages combined with optimized signal frequencies and extended integration times. This parameter transformation allows achieving sufficient signal strength for accurate capacitance measurement without the harmful electromagnetic interference associated with high-voltage approaches.
Solution Approach 2:
The patent replaces the mechanical/electrical approach of increasing voltage to improve signal strength with a signal processing approach. By using correlated sampling, digital filtering, and frequency-domain analysis, the system achieves high measurement precision without relying on high voltages, thereby eliminating the associated electromagnetic interference problems.
3Productivity
If higher test-signal frequencies are used to increase measurement speed, then the measurement time is improved, but electromagnetic interference and row interaction increase
Solution Approach 1:
The patent uses periodic drive signals at carefully selected frequencies that balance measurement speed with interference minimization. By optimizing the frequency of periodic excitation signals, the system achieves fast measurement cycles without the excessive electromagnetic interference and row coupling effects that occur at higher frequencies.
Solution Approach 2:
The patent employs feedback mechanisms where the measured signals are correlated with the known drive signals, and the results are used to adjust subsequent measurements. This feedback approach allows the system to achieve high effective measurement speed through signal processing rather than raw frequency increases, avoiding the harmful effects of high-frequency operation.
4Stability of the object's composition
If the scan time is fixed by physical factors, then the measurement stability is improved, but the power consumption increases for larger panels
Solution Approach 1:
The patent segments the panel measurement into multiple smaller measurement cycles or regions. By dividing the total measurement task into segments that can be performed with lower power per cycle, the system maintains measurement stability through multiple passes while reducing the instantaneous power consumption compared to attempting to measure the entire large panel simultaneously at high power 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
The system enables reliable and precise multi-touch sensing on large panels with reduced electromagnetic interference and power consumption, allowing for longer sensing times and improved spatial resolution.
Implementation Method 1
measuring changes in mutual capacitances between rows and columns of a grid of conductors on the panel
Implementation Method 2
estimate coupling capacitances by correlating digitized received signals with the overlapping but mathematically independent drive signals
Data Source
AI summary
A multi-touch sensing system and a method for estimating a location of at least one touch point are provided. The multi-touch sensing system includes a panel, a grid of conductor disposed on the panel, a driver array connected to the grid, a receiver array connected to the grid, a signal processing system, and a controller. The method involves transmitting drive signals to the grid, receiving signals from the grid, estimating a capacitance, and transforming the capacitance into touch coordinates.