Mutual Capacitance Sensing With Operational Amplifier
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Solution Overview
Problem
Capacitive touch screen panels face challenges in accurately detecting touch events due to noise interference across narrow frequency bands, leading to false indications and reduced reliability.
Innovation Solution
The system employs a wideband frequency input signal transmission and reception, using state machines to filter out noise at other frequencies, and directly amplifies mutual capacitance between input and output lines using operational amplifiers to enhance signal detection and reduce electromagnetic emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If narrow frequency band transmission is used, then power consumption is reduced, but signal-to-noise ratio deteriorates and false detections increase
Solution Approach 1:
The system dynamically adjusts the frequency band width based on operating conditions. The wideband frequency input signal is transmitted during phases requiring high reliability, while narrowband transmission is used during power-saving phases. This dynamic switching resolves the contradiction between power consumption and signal-to-noise ratio.
Solution Approach 2:
The patent changes the frequency parameter of the transmission signal from narrowband to wideband to improve signal-to-noise ratio when needed. The state machine controller switches between different frequency band configurations, allowing the system to optimize between power consumption and detection reliability based on current operational requirements.
2Reliability
If wideband frequency input signal is transmitted, then signal-to-noise ratio is improved, but electromagnetic emissions increase
Solution Approach 1:
The system uses periodic wideband frequency input signal transmission rather than continuous transmission. The state machine controller activates wideband transmission only during specific measurement phases, allowing the system to achieve high signal-to-noise ratio when needed while minimizing overall electromagnetic emissions through intermittent operation.
Solution Approach 2:
The system dynamically controls the transmission of wideband signals based on operational requirements. During touch detection phases, wideband signals are transmitted to maximize signal-to-noise ratio, while during idle phases, transmission is reduced or eliminated to minimize electromagnetic emissions. This dynamic control resolves the contradiction between reliability and harmful emissions.
3Measurement precision
If mutual capacitance is directly amplified, then touch detection sensitivity is improved, but circuit complexity increases
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary component to directly amplify the mutual capacitance signal between input and output lines. This intermediary device enhances touch detection sensitivity by amplifying the capacitance change signal while the state machine controller manages the overall system operation, keeping the control logic integrated and minimizing additional circuit complexity.
Solution Approach 2:
The operational amplifier is integrated into the existing touch sensor circuitry, merging the amplification function with the capacitance measurement function. The input line and output line of the touch sensor are directly connected to the operational amplifier, combining multiple functions (capacitance sensing, signal amplification, and measurement) into a unified circuit structure that improves sensitivity without proportionally increasing 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
This approach results in a more reliable touch screen panel with improved signal-to-noise ratio and reduced power consumption, while minimizing false touch event detections and electromagnetic interference.
Implementation Method 1
a mutual capacitance between the input line and the output line is directly amplified using miller amplification
Implementation Method 2
the capacitive touch sensor converts the touch point information into an electrical signal by sensing a change in capacitance formed between a conductive sensing electrode and an adjacent (or overlapping) sensing electrode or ground electrode
Data Source
AI summary
A display device includes: a display panel configured to display an image at an active area; a touch screen panel overlapping the display panel at the active area, the touch screen panel comprising an input line and an output line; and an operational amplifier having an input electrode coupled to the input line and an output electrode coupled to the output line, wherein the display device is configured to measure a voltage at the output electrode of the operational amplifier for detecting a touch event at an intersection between the input line and the output line.