Touch Panel Noise-Canceling Circuit With Feedback Voltage Clamping
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Solution Overview
Problem
Touch panels in display systems face interference from underlying display systems due to large voltage pulses, causing saturation and impairing touch detection.
Innovation Solution
Implementing a capacitive touch panel with clamping and correction mechanisms to manage overvoltage and undervoltage, using threshold comparators and transconductance amplifiers to maintain signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the touch panel is placed close to the display system, then the display area is maximized and device integration is improved, but electrical interference from the display system couples to the touch panel electrodes causing circuit saturation
Solution Approach 1:
A ground plane is introduced as an intermediary element between the display system and the touch panel. This ground plane acts as a shield that blocks electrical interference from coupling to the touch panel electrodes while allowing the display system to operate at high voltage pulses. The ground plane mediates the electromagnetic interaction, protecting the touch sensor from harmful signals.
Solution Approach 2:
The patent utilizes the common mode noise generated by the display system in a creative way. By introducing the ground plane, the harmful interference is redirected to serve as a reference signal for noise cancellation techniques. The common mode noise that would normally saturate the circuits is instead used to generate cancellation signals that actively remove the interference from the touch panel electrodes.
2Illumination intensity
If large voltage pulses are used to drive the display system, then display brightness and visibility are improved, but the coupled electrical interference saturates the touch sensor circuits
Solution Approach 1:
The patent implements feedback mechanisms through noise cancellation circuits that continuously monitor the electrical interference on the touch panel electrodes. The system generates cancellation signals based on the detected interference patterns and feeds these back to actively neutralize the coupling noise. This feedback loop allows the system to maintain accurate touch detection even when large voltage pulses are used for display driving.
Solution Approach 2:
The common mode noise generated by the large voltage pulses is converted into a useful reference signal. The noise cancellation circuitry uses this previously harmful interference as the basis for generating cancellation signals that actively remove the interference from the touch sensor electrodes, thereby enabling reliable touch detection alongside high-brightness display operation.
3Speed
If the touch panel electrodes are driven at high frequency, then touch response speed is improved, but the interference from the display system falls within the same frequency band making filtering difficult
Solution Approach 1:
The ground plane serves as an intermediary that spatially separates the electromagnetic fields of the display system from the touch panel electrodes. This physical mediation allows the touch panel to operate at high frequencies without the interference falling directly onto the sensor electrodes, enabling effective filtering even when the interference frequency overlaps with the touch sensing frequency.
Solution Approach 2:
The patent converts the harmful high-frequency interference into a useful reference signal for active noise cancellation. By using the common mode noise as a reference, the system generates cancellation signals that actively subtract the interference from the touch sensor readings, enabling accurate touch detection at high frequencies despite the overlapping frequency bands.
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
Effectively reduces electrical interference, preserving touch sensing functionality by preventing circuit saturation and maintaining signal fidelity.
Implementation Method 1
clamping the feedback voltage to a first upper voltage threshold in response to a first voltage difference between the feedback voltage and the reference voltage being greater than the first upper voltage threshold
Implementation Method 2
an amplifier configured to generate a time-variant line voltage across the capacitive load in response to a reference voltage difference
Implementation Method 3
a capacitive touch panel having a capacitive load, wherein the capacitive load is alterable by a physical touch
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A method for display noise canceling in a touch sensing system includes measuring a first feedback voltage of a feedback node resistively coupled to a line voltage of a capacitive touch panel, the line voltage formed by a continuous wave output of an amplifier responsive to a reference voltage difference between the first feedback voltage and a reference voltage. A second feedback voltage is clamped to a first upper voltage threshold in response to a first voltage difference between the first feedback voltage and the reference voltage being greater than the first upper voltage threshold. The second feedback voltage is clamped to a first lower voltage threshold in response to the first voltage difference being less than the first lower voltage threshold.