Touch Panel Pressure Sensing With Differential Piezoelectric Readout
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Solution Overview
Problem
Projected capacitance touch panels struggle to differentiate between light taps and heavy presses due to the inability to sense pressure, leading to inaccurate interaction detection.
Innovation Solution
A method and apparatus that utilize differential piezoelectric measurements to separate and enhance desired pressure signals while reducing interference from external electric fields by combining signals from electrodes on opposite sides of a piezoelectric material layer, employing a differential amplifier configuration to cancel out common-mode interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If projected capacitance touch panels are used to detect touch location, then touch position accuracy is improved, but pressure sensing capability deteriorates (cannot distinguish between light taps and heavy presses)
Solution Approach 1:
The touch panel system is segmented into multiple independent sensing layers: a capacitive sensing layer for detecting touch position and a piezoelectric sensing layer for detecting pressure magnitude. Each layer performs its specialized function independently, with the capacitive sensors tracking finger position and the piezoelectric sensors measuring the force applied, thereby resolving the contradiction between position accuracy and pressure information capture
Solution Approach 2:
The patent merges capacitive and piezoelectric sensing technologies into a single integrated touch panel system. The capacitive and piezoelectric sensor arrays are positioned in close proximity (with spacing less than 1mm) to detect the same touch event from different physical principles, allowing simultaneous acquisition of both position and pressure data without interference
2Measurement precision
If piezoelectric sensors are used to detect pressure, then pressure measurement capability is improved, but susceptibility to external electric field interference worsens
Solution Approach 1:
The patent converts the harmful effect of external electric fields into a useful signal by measuring the differential voltage between two piezoelectric sensors. When an external electric field interferes, it affects both sensors equally, creating a common-mode signal that contains information about the interference itself. By measuring the difference between the two sensors, the system can identify and compensate for this interference, transforming the harmful effect into a calibratable parameter
Solution Approach 2:
The system dynamically adjusts the measurement parameters by switching between absolute pressure measurement mode and differential pressure measurement mode. In environments with significant external electric field interference, the system transitions to differential mode, where the measurement parameter changes from absolute pressure to pressure difference, thereby reducing the impact of common-mode interference while maintaining accurate pressure detection capability
3Adaptability or versatility
If multiple sensor arrays are integrated for combined capacitance and pressure sensing, then sensing versatility is improved, but device complexity increases
Solution Approach 1:
The patent implements a universal sensor interface architecture that can handle both capacitive and piezoelectric sensor signals through a single readout circuitry. The system uses a unified data acquisition and processing framework that automatically adapts to the appropriate sensing mode based on the input signal characteristics, allowing the same hardware infrastructure to support multiple sensing modalities without requiring separate dedicated systems for each type
Solution Approach 2:
The patent replaces complex mechanical pressure sensing mechanisms with piezoelectric material-based sensing. Instead of using mechanical springs, levers, or force sensors, the system utilizes the piezoelectric effect where mechanical stress directly generates electrical signals. This substitution simplifies the mechanical structure while enabling precise pressure measurement, reducing overall device complexity despite the addition of sensing versatility
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
Enables accurate detection of applied forces by minimizing interference, allowing for precise differentiation between varying levels of pressure on touch panels.
Implementation Method 1
A pressure sensitive touch panel includes a layer of piezoelectric material between a common electrode and a number of sensing electrodes
Data Source
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AI summary
Apparatus (104) for processing signals from a touch panel (108) that includes a piezoelectric material layer (16) disposed between a number of sensing electrodes (14,20) and one or more common electrodes (105). The apparatus includes a capacitive touch controller (69) for connection to the sensing electrodes; a switch network (74) including a number of inputs connected to some or all sensing electrodes, and an output connected to system ground or a common mode voltage (VCM); a second circuit (106) for connection to the one or more common electrodes and configured to generate, for each common electrode, a corresponding pressure signal (30) indicative of a pressure applied proximate to that common electrode and a controller (25) configured during the pressure measurement period to control the switch network to couple any connected sensing electrodes to system ground or the common mode voltage and to sample the pressure signals.