Multitouch Capacitive Detection Resolving Phantom Presses
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Solution Overview
Problem
Multitouch touch devices employing projected capacitive detection struggle to accurately distinguish between real and phantom presses, especially when multiple presses occur, leading to incorrect detection and reduced functionality.
Innovation Solution
A multitouch touch device employing a touch matrix array with voltage-generating means that apply different frequencies to rows and columns to generate output voltages, using synchronous demodulation and reference values to differentiate between real and phantom presses, thereby improving the accuracy of press detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If self-capacitive detection is used to detect multiple presses, then the detection range is improved, but phantom presses cannot be distinguished from real presses
Solution Approach 1:
The patent segments the detection process into two distinct phases: self-capacitance measurement for initial press detection and mutual capacitance measurement for verification. This segmentation allows the system to first identify potential presses using self-capacitance and then verify them using mutual capacitance, thereby distinguishing real presses from phantom presses while maintaining multi-touch capability
Solution Approach 2:
The patent introduces mutual capacitance measurement as an intermediary verification step between initial press detection and final press confirmation. This intermediary measurement acts as a filter that validates whether detected presses are real or phantom, resolving the contradiction between detection range and accuracy
2Reliability
If emission voltages at two different frequencies are applied to eliminate phantom presses, then the reliability of press detection is improved, but the device complexity increases
Solution Approach 1:
The patent employs periodic action by applying emission voltages at two different frequencies in alternating cycles. The system periodically switches between self-capacitance measurement mode and mutual capacitance measurement mode, using frequency-based temporal separation to distinguish real presses from phantom presses without requiring complex hardware modifications
Solution Approach 2:
The patent changes the frequency parameter of emission voltages to differentiate between measurement types. By using distinct frequencies for self-capacitance and mutual capacitance measurements, the system can process and distinguish the resulting signals through frequency-based filtering and demodulation, improving reliability while managing complexity through parameter differentiation rather than structural complexity
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 solution effectively discriminates between real and phantom presses, enabling the accurate detection of multiple presses and enhancing the usability of touch screen devices by reducing electromagnetic interference and improving signal clarity.
Implementation Method 1
detect the local variations in capacitance introduced by the proximity of the fingers of the user or of any other conductive object. Thus, when a finger touches the surface, an electrical capacitance is formed between the finger and the sensor grid
Implementation Method 2
The processing means comprise a first synchronous demodulator configured to operate at the first frequency, receive the first output voltage so as to produce a first DC output voltage
Data Source
AI summary
A multitouch touch device (DIS) employing capacitive detection, including: a touch matrix array and a first voltage-generating source configured to generate, for each row and each column of the matrix array, a first input voltage having a first frequency leading to the generation of a first output voltage. The device also includes a second voltage-generating source for generating, for each intersection between at least two rows and two columns of the matrix array, a second input voltage having a second frequency different from the first frequency leading to the generation of a second output voltage. A processing circuit is configured to determine, depending on first and second reference values, whether the first and second output voltages are representative of a press and of its position.