Touch Panel Sensing Circuit With Parasitic Capacitance Cancellation
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Solution Overview
Problem
Conventional touch panel sensing circuits are hindered by parasitic capacitance, leading to reduced sensitivity and slower sensing speeds due to the influence of parasitic capacitance on the coupling capacitance and charge integrator, resulting in smaller voltage variations and longer detection times.
Innovation Solution
A touch panel sensing circuit design that incorporates an input voltage source, multiple voltage switches, a common voltage source, an amplifier, and feedback capacitors to accumulate and amplify charge differences over multiple clock cycles, while switching mechanisms and virtual grounding minimize the impact of parasitic capacitance, allowing for faster and more sensitive detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sensing circuit uses coupling capacitance and charge integrator, then the circuit can detect touch, but the parasitic capacitance of sensing lines reduces the coupling charge amount and output voltage variation
Solution Approach 1:
The patent extracts and separates the parasitic capacitance measurement from the mutual capacitance measurement by introducing dedicated test signal paths. The test signal is applied to sensing lines individually while isolating them from the normal touch detection path, allowing the parasitic capacitance to be measured and compensated independently without affecting the primary touch sensing function.
Solution Approach 2:
The patent changes the operational parameters by introducing test signals with specific frequencies and amplitudes that allow differentiation between parasitic capacitance and mutual capacitance effects. By varying the signal state (active/test modes) and measuring different parameter combinations, the system can separate and compensate for parasitic effects mathematically.
2Power
If the charge integrator divides coupling charge with parasitic capacitance, then the circuit operates, but the output voltage variation becomes smaller reducing amplifier detection capability
Solution Approach 1:
The patent implements feedback by measuring the parasitic capacitance values and using this information to compensate for their effect on the charge integrator output. The system feeds back the measured parasitic parameters to adjust the detection algorithm or signal processing, thereby recovering the voltage variation that would otherwise be lost to parasitic effects.
Solution Approach 2:
The patent introduces test signals and measurement circuits as intermediaries between the sensing lines and the charge integrator. These intermediaries allow the system to characterize and account for parasitic capacitance effects without letting them directly degrade the main detection signal, acting as a buffer that separates the harmful effect from the useful measurement.
3Measurement precision
If additional clock cycles are required to accumulate sufficient charge, then the sensing speed and sensitivity are reduced
Solution Approach 1:
The patent performs preliminary measurement of parasitic capacitance values before the main touch detection process. By characterizing the parasitic effects in advance during manufacturing or initialization, the system can compensate for them during normal operation without requiring additional measurement time, thus maintaining fast sensing speed while achieving accurate charge accumulation.
Solution Approach 2:
The patent uses periodic test signals to measure parasitic capacitance at regular intervals rather than continuously. This periodic measurement approach allows the system to update compensation parameters efficiently without occupying the sensing lines continuously, maintaining high sensing speed while periodically refreshing the parasitic capacitance data for accurate charge accumulation compensation.
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 enhances the sensitivity and speed of touch detection by increasing the accumulated charge difference with each clock cycle, effectively canceling the effect of parasitic capacitance and improving signal-to-noise ratio, thus enabling quicker operation and reduced power consumption.
Implementation Method 1
a coupling capacitor formed between a first directional signal line and a second directional signal line separated from the first directional signal line by a dielectric
Implementation Method 2
senses a voltage variation of a coupling capacitor formed between a first directional signal line and a second directional signal line separated from the first directional signal line by a dielectric
Data Source
AI summary
A touch panel sensing circuit senses a voltage variation of a coupling capacitor formed between a first directional signal line and a second directional signal line separated from the first directional signal line by a dielectric when an object approaches. The sensing circuit eliminates the parasitic capacitance effect on the signal lines and rapidly accumulates charges for an amplifier in sensing to thereby increase the operational speed of the sensing circuit.