Current-Driven Touch Sensing With Parasitic Capacitance Separation
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Solution Overview
Problem
In touch sensing devices, parasitic capacitance between the touch screen panel and peripheral conductors can reduce touch sensitivity and saturate the sensing amplifier's output range, leading to increased noise and decreased signal quality.
Innovation Solution
A current driving type touch sensing device that uses an electric charge controller to charge and discharge parasitic capacitors separately, allowing the sensing unit to drive only the intended capacitors, thereby minimizing internal noise and stabilizing the sensing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a feedback capacitor is added to the sensing amplifier to compensate for parasitic capacitance, then the parasitic capacitance effect is reduced, but the output voltage level decreases and device complexity increases
Solution Approach 1:
The patent segments the capacitance compensation function by separating the parasitic capacitance compensation from the sensing amplifier. Instead of adding components to the amplifier, it uses a dedicated parasitic capacitance compensation circuit that operates independently, thus reducing the complexity of the sensing amplifier while still achieving compensation.
Solution Approach 2:
The patent extracts the parasitic capacitance compensation function from the sensing amplifier and implements it as a separate compensation circuit. This extraction allows the sensing amplifier to maintain its original simple structure while the compensation function is handled by the dedicated circuit, resolving the contradiction between compensation effectiveness and device complexity.
2Measurement precision
If an offset removal circuit is added to the sensing amplifier to eliminate parasitic capacitance effects, then the sensing accuracy is improved, but internal noise increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The patent extracts the offset removal function from the sensing amplifier and implements it in a separate compensation circuit. This separation allows the sensing amplifier to operate without the additional noise-generating components, maintaining high signal-to-noise ratio while still achieving accurate touch sensing through the dedicated compensation circuit.
Solution Approach 2:
The patent introduces an intermediary compensation circuit that handles the offset removal and parasitic capacitance compensation functions. This intermediary circuit acts as a mediator between the touch electrode and the sensing amplifier, performing the necessary signal conditioning without introducing the noise that would result from adding circuits directly to the amplifier.
3Reliability
If the feedback capacitor value is increased to compensate for parasitic capacitance, then the compensation effect is improved, but the output voltage level decreases
Solution Approach 1:
The patent changes the approach from adjusting capacitor values to adjusting voltage levels. Instead of increasing the feedback capacitor value (which would reduce output voltage), the compensation circuit adjusts the voltage applied to the touch electrode to compensate for parasitic capacitance effects, thereby maintaining both compensation effectiveness and output voltage level.
Solution Approach 2:
The patent extracts the compensation function from the feedback capacitor and implements it as a separate voltage control circuit. This allows the feedback capacitor to maintain its original value and function while the compensation is achieved through voltage adjustment in the dedicated circuit, preserving the output voltage level.
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 enhances touch sensitivity, reduces internal noise, and increases the signal-to-noise ratio (SNR) of the touch sensing signal, while also reducing the size of the feedback capacitor and increasing the output voltage level.
Implementation Method 1
a parasitic capacitance charger connected to a touch sensing line to charge a parasitic capacitor of a touch electrode connected to the touch sensing line with a predetermined charging current during a charging period
Implementation Method 2
a sensing unit connected to the touch sensing line during a first driving period to drive a capacitor of the touch electrode with a first driving current corresponding to a difference voltage between a first voltage, charged into the parasitic capacitor when a touch does not occur, and a second voltage charged into the parasitic capacitor when a touch occurs
Data Source
AI summary
A touch sensing device of a current driving type, which separately drives a parasitic capacitor by using an electric charge controller, includes a parasitic capacitance charger connected to a touch sensing line to charge a parasitic capacitor of a touch electrode connected to the touch sensing line with a predetermined charging current during a charging period and a sensing unit connected to the touch sensing line during a first driving period to drive a capacitor of the touch electrode with a first driving current corresponding to a difference voltage between a first voltage, charged into the parasitic capacitor when a touch does not occur, and a second voltage charged into the parasitic capacitor when a touch occurs and to sense a first touch voltage of the capacitor based on the first driving current during a first sensing period.