Charge Transfer Circuit With AVF for Parasitic Capacitance Compensation
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Solution Overview
Problem
Capacitive sensors, such as touch screen panels, face reduced touch sensitivity and accuracy due to parasitic capacitance and resistance, which are exacerbated by the use of discrete time integrators that only utilize half of the supply voltage in a touch state, leading to deteriorated performance.
Innovation Solution
A charge transfer circuit with an active output voltage feedback (AVF) system, including a variable capacitor, X-drive and Y-drive units, and parasitic resistors and capacitors, where the AVF part feeds back the output voltage to charge the parasitic capacitor, maintaining voltage equality and minimizing parasitic effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If discrete time integrators are used to reduce parasitic effects, then parasitic capacitance impact is reduced, but touch sensitivity deteriorates due to using only half of supply voltage
Solution Approach 1:
The patent implements active output voltage feedback (AVF) that continuously monitors the output voltage and feeds it back to the summing node through a feedback capacitor. This feedback mechanism compensates for parasitic capacitance effects by dynamically adjusting the integration process, allowing the system to maintain both low parasitic impact and high touch sensitivity across the full supply voltage range.
Solution Approach 2:
The patent changes the operating parameters by utilizing the full supply voltage range through the AVF configuration. The feedback mechanism enables the integrator to operate effectively across the complete voltage swing, doubling the effective voltage utilization compared to conventional discrete time integrators and thereby improving touch sensitivity while maintaining parasitic rejection.
2Area of stationary object
If electrodes with parasitic elements are used in touch screen panels, then display unit size can be increased, but touch sensitivity and accuracy reduce due to parasitic capacitance and resistance
Solution Approach 1:
The AVF circuit continuously monitors output voltage and compensates for parasitic effects through feedback action. This allows large display units with necessarily larger parasitic elements to maintain high touch sensitivity and accuracy, as the feedback mechanism dynamically counteracts the parasitic capacitance and resistance effects across the entire display area.
Solution Approach 2:
The patent extracts and separately manages the parasitic effects by introducing dedicated feedback capacitors and resistors that specifically target parasitic capacitance compensation. This separation allows the main electrodes to be sized for large displays while the feedback network handles the parasitic compensation independently.
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 maintains linearity and enhances touch sensitivity over a wide dynamic range by effectively eliminating the parasitic effect, as demonstrated by the voltage difference and sensitivity analysis in the charge transfer circuit diagrams and graphs.
Implementation Method 1
a variable capacitor disposed between the output terminal of an X-drive line and the input terminal of a Y-drive line
Implementation Method 2
an active output voltage feedback (AVF) part connected between the output terminal of the Y-drive line and a voltage output terminal; wherein the output terminal of the AVF part is connected to the output terminal of the Y-drive line
Data Source
AI summary
A charge transfer circuit for capacitive sensing is disclosed. The charge transfer circuit for capacitive sensing includes a variable capacitor, an X-drive unit, and an active output voltage feedback (AVF) part. The variable capacitor is disposed between the output terminal of an X-drive line and the input terminal of a Y-drive line. The X-drive unit is connected between the input unit of the X-drive line and a voltage input terminal. The active output voltage feedback (AVF) part is connected between the output terminal of the Y-drive line and a voltage output terminal. The output terminal of the AVF part is connected to the output terminal of the Y-drive line.