Differential Touch Sensing Front-End for Display Noise Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-speed driving, thinning, and enlargement of display devices lead to reduced touch sensing sensitivity due to increased parasitic capacitance and noise interference from display driving signals, affecting the performance of touch sensors.
Innovation Solution
An input sensing device with driving electrodes and sensing electrodes, featuring an analog front-end that differentially amplifies and filters signals using charge amplifiers and demodulation circuits, and a signal processor to enhance sensing sensitivity by reducing noise and parasitic capacitance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the display device is driven at high speed (increased from 60 Hz to 120 Hz), then the display performance is improved, but the period of the driving signal is reduced and time for touch sensing is reduced
Solution Approach 1:
The patent applies periodic action by using alternating current (AC) driving signals with specific frequencies for both the display panel and touch panel. The touch panel driving signal is synchronized with the display driving signal at a 1:2 frequency ratio, creating periodic cycles where touch sensing occurs during specific time windows within each display refresh cycle. This periodic structure allows the system to maintain high-speed display operation while allocating dedicated time periods for touch sensing.
Solution Approach 2:
The patent implements dynamics by making the touch panel driving signal frequency adaptive and可调 (adjustable) based on the display driving frequency. When the display operates at 60 Hz, the touch panel drives at 60 Hz; when the display increases to 120 Hz, the touch panel automatically adjusts to 120 Hz. This dynamic adjustment maintains optimal sensing conditions across different operating speeds.
2Length of moving object
If the display device is thinned and enlarged, then the device form factor is improved, but the distance between display panel and touch panel is reduced and parasitic capacitance is increased
Solution Approach 1:
The patent converts the harmful effect of increased parasitic capacitance into a beneficial signal. By using AC coupling and differential sensing, the parasitic capacitance between the display panel and touch panel, which would normally degrade sensing performance, is transformed into part of the sensing mechanism. The system measures capacitance changes relative to this parasitic baseline, allowing touch detection to proceed accurately despite the reduced distance.
Solution Approach 2:
The patent applies parameter changes by adjusting the driving frequency and voltage parameters of the touch panel electrodes. The AC driving voltage amplitude is set to 3-5 Vpp, and the frequency is synchronized with the display panel. These parameter optimizations compensate for the reduced distance effect and maintain sensing sensitivity even with increased parasitic capacitance.
3Speed
If the display driving signal frequency is increased, then the display refresh rate is improved, but noise interference to the touch panel is increased
Solution Approach 1:
The patent introduces AC coupling capacitors as intermediary elements between the display driving circuit and the touch panel. These capacitors block direct DC coupling that would transmit noise, while allowing AC touch sensing signals to pass. The differential sensing architecture acts as another intermediary layer that rejects common-mode noise from the display driving signals, isolating the touch sensing path from electromagnetic interference.
Solution Approach 2:
The patent applies equipotentiality by using differential sensing with balanced signal paths. The touch sensing circuit measures the difference between two symmetric signal paths, causing common-mode noise from the display driving signal to cancel out. This equipotential approach ensures that noise affecting both paths equally does not contribute to the measured touch signal.
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 increases sensing sensitivity and accuracy in environments with deteriorated touch sensor performance, ensuring reliable touch input detection even under high-speed and thin-film conditions.
Implementation Method 1
a first charge amplifier configured to differentially amplify a first sensing signal and a second sensing signal provided from two sensing electrodes among the sensing electrodes to first and second input terminals, thus outputting a first differential signal and a second differential signal
Implementation Method 2
a first demodulation circuit configured to filter each of the first and second differential signals in a first mode, and to filter each of the third and fourth differential signals in a second mode
Implementation Method 3
The touch panel may include a plurality of sensing electrodes, and may determine a touched point by sensing a change in capacitance formed on a plurality of touch electrodes
Data Source
AI summary
An input sensing device includes driving electrodes and sensing electrodes, and an analog front-end which processes sensing signals from the sensing electrodes to output a differential output value. The analog front-end includes a first charge amplifier which differentially amplifies first and second sensing signals from two sensing electrodes to first and second input terminals, thus outputting first and second differential signals through first and second output terminals, a second charge amplifier which differentially amplifies the first and second differential signals, thus outputting third and fourth differential signals, a first demodulation circuit which filters the first and second differential signals in a first mode and filters each of the third and fourth differential signals in a second mode, and a first analog-to-digital converter which outputs a first sensing value based on at least one output signal of the first demodulation circuit.