Sync Signal Generator for Capacitive Sensor Noise Filtering
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Solution Overview
Problem
One-layer capacitive touch-screen sensor panels lack a GND layer, leading to noise interference from VCOM voltage in LCD modules, which existing systems struggle to filter out without a direct electrical connection for synchronization.
Innovation Solution
A sync signal generator that includes a charge amplifier, comparators, and digital-to-analog converters to generate SYNC signals for synchronizing touch sensor timing with VCOM activity, allowing noise filtering without a separate HSYNC connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a one-layer sensor panel is used to reduce cost and simplify structure, then manufacturing cost and structural complexity are reduced, but noise shielding capability deteriorates due to the absence of a GND layer
Solution Approach 1:
The patent introduces an intermediary GND layer between the LCD module and the sensor panel to shield against VCOM noise. This intermediate layer acts as a mediator that blocks harmful electromagnetic interference from reaching the sensor, resolving the contradiction between simplified one-layer structure and noise shielding capability.
Solution Approach 2:
The patent converts the harmful VCOM noise into a useful synchronization signal by detecting the noise characteristics and using them to generate HSYNC signals for coordinating sensor measurements with LCD refresh cycles, thereby turning the harmful interference into a beneficial timing reference.
2Reliability
If the VCOM voltage changes are detected to filter noise, then noise filtering capability is improved, but the complexity of the synchronization system increases
Solution Approach 1:
The system uses the sensor panel's own receive lines to detect VCOM noise and generate synchronization signals, eliminating the need for external HSYNC connections from the LCD driver. The sensor system serves itself by utilizing its existing infrastructure for both sensing and noise detection, reducing overall system complexity while maintaining reliable noise filtering.
3Measurement precision
If a direct electrical connection is made to the LCD driver for HSYNC signal acquisition, then synchronization accuracy is improved, but adaptability to different LCD modules deteriorates
Solution Approach 1:
The patent creates a copy of the HSYNC signal by detecting VCOM noise characteristics on the sensor panel's receive lines and generating synchronization signals locally. This copied signal achieves the same synchronization function without requiring direct electrical connection to the LCD driver, thereby maintaining synchronization accuracy while improving compatibility with different LCD modules.
4Object-generated harmful factors
If charge is injected into the capacitance formed by receive line and VCOM layer during VCOM switching, then the VCOM signal coupling effect is enhanced, but noise detection accuracy deteriorates
Solution Approach 1:
The patent performs preliminary actions by detecting VCOM switching events and generating synchronization signals before actual capacitance measurements are taken. This allows the system to coordinate measurement timing with VCOM activity, ensuring measurements are taken during stable periods when noise coupling is minimal, thereby maintaining measurement accuracy despite the presence of strong VCOM noise coupling effects.
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 effective noise filtering and synchronization of touch sensor operations with VCOM activity, making the system compatible with all LCD displays without the need for a specific electrical connection.
Implementation Method 1
A portion 100 of the sensor panel according to the prior art is shown in which the VCOM layer 104, capacitive layer 106, and a representative receive line 102 are shown in plan view and in a cross-sectional view. The receive line 102 and the VCOM layer 104 in a laminated capacitive sensor panel form a capacitance CX
Implementation Method 2
a first comparator having a first input for receiving a first threshold voltage, a second input coupled to an output of the charge amplifier, and an output for providing a first sync signal, and a second comparator having a first input for receiving a second threshold voltage, a second input coupled to the output of the charge amplifier, and an output for providing a second sync signal
Data Source
AI summary
A sync signal generator for a capacitive sensor includes a charge amplifier having an input for coupling to an inactive receive line in the capacitive sensor, a first comparator having a first input for receiving a first threshold voltage, a second input coupled to an output of the charge amplifier, and an output for providing a first sync signal, and a second comparator having a first input for receiving a second threshold voltage, a second input coupled to the output of the charge amplifier, and an output for providing a second sync signal. The charge amplifier includes an operational amplifier having a feedback circuit including a capacitor and a switch. The first threshold voltage is provided by a first digital-to-analog converter, and the second threshold voltage is provided by a second digital-to-analog converter.