Analog Front-End Differential Sensing for Noisy Thin Displays
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Solution Overview
Problem
High-speed driving and thinning of display devices lead to reduced touch sensing sensitivity due to increased parasitic capacitance and decreased time for touch sensing, exacerbated by the noise interference from display driving signals.
Innovation Solution
An analog front-end system with charge amplifiers and demodulation circuits that differentially amplify and filter sensing signals from touch electrodes, reducing noise interference and enhancing sensitivity by converting and processing touch signals effectively.
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 display driving signal is decreased and the time for touch sensing is reduced
Solution Approach 1:
The patent implements a dual-frequency driving scheme where the display panel is driven at a first frequency (e.g., 60 Hz) and the touch sensing is performed at a second frequency (e.g., 120 Hz). This periodic action with different frequencies allows the touch sensing to complete its measurement cycle within the available time window, effectively resolving the time constraint imposed by high-speed display driving.
2Length of moving object
If the display device becomes thinner and/or increases in size, then the device form factor is improved, but the gap between the display panel and the touch panel is reduced and parasitic capacitance increases
Solution Approach 1:
The patent changes the frequency parameter of touch sensing to a second frequency that is different from (typically higher than) the first frequency of display driving. This parameter change allows the touch sensing operation to be completed within the reduced time window created by the thinner device structure, thereby compensating for the increased parasitic capacitance effect.
3Area of stationary object
If the overlapping area between the display panel and the touch panel increases, then the device coverage is improved, but parasitic capacitance increases and sensing sensitivity decreases
Solution Approach 1:
By implementing touch sensing at a second frequency that operates periodically within the display driving cycle, the patent enables the sensing operation to complete its measurement within the available time window. This periodic action at differentiated frequencies maintains sensing sensitivity even when the overlapping area increases and parasitic capacitance rises.
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 increases touch sensing sensitivity and reduces signal processing load, effectively addressing the challenges of high-speed driving and thin display devices by filtering noise and improving signal quality.
Implementation Method 1
The (1-1)-th charge amplifier is configured to differentially amplify a first sensing signal and a second sensing signal provided to the (1-1)-th input terminal and the (1-2)-th input terminal, respectively
Implementation Method 2
A demodulation circuit is configured to filter the (2-1)-th differential signal and the (2-2)-th differential signal and output demodulated differential signals
Implementation Method 3
the display device may be an input sensing device that detects a touched point on the touch panel and determines a position of the touched point by sensing a change in capacitance formed in a plurality of touch electrodes
Data Source
AI summary
An analog front-end includes a (1-1)-th charge amplifier configured to differentially amplify a first and second sensing signals provided to a (1-1)-th input terminal and a (1-2)-th input terminal, respectively, and output a (1-1)-th differential signal. A (1-2)-th charge amplifier is configured to differentially amplify the second sensing signal and a third sensing signal provided to a (1-3)-th input terminal and a (1-4)-th input terminal, respectively, and output a (1-2)-th differential signal. A second charge amplifier is configured to differentially amplify the (1-1)-th differential signal and the (1-2)-th differential signal provided to a (2-1)-th input terminal and a (2-2)-th input terminal, respectively, and output a (2-1)-th differential signal and a (2-2)-th differential signal. A demodulation circuit is configured to filter the (2-1)-th differential signal and the (2-2)-th differential signal and output demodulated differential signals. An analog-to-digital converter is configured to output a sensing value based on the demodulated differential signals.