Touch Panel Capacitance Measurement Circuit
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Solution Overview
Problem
Conventional touch panels consume high energy due to their inability to accurately detect small capacitance differences, leading to inefficient operation and increased energy consumption.
Innovation Solution
A touch panel design incorporating a first clock phase generator, six switches, and a control circuit that generates phase signals to accurately determine the capacitance of a panel capacitor by charging and discharging capacitors in a controlled manner, using a second capacitor to compensate for capacitance differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the ADC converts the capacitance of the UUT continuously, then the touch panel can detect capacitance variations, but the energy consumption increases significantly
Solution Approach 1:
The patent implements periodic sampling of the panel capacitor's voltage instead of continuous conversion. The control circuit samples the voltage at specific time points during charging/discharging cycles, converting capacitance values periodically rather than continuously. This periodic action maintains detection capability while significantly reducing ADC operation frequency and energy consumption.
Solution Approach 2:
The patent performs preliminary charging and discharging of the panel capacitor through controlled switch operations before measurement. By pre-charging the capacitor to a known voltage state and then discharging through a known resistance, the system establishes predictable voltage-time characteristics that enable accurate capacitance measurement at specific sampling points without requiring continuous monitoring.
2Device complexity
If the touch panel uses a simple capacitance measurement method, then the device complexity is reduced, but the sensitivity to detect small capacitance differences deteriorates
Solution Approach 1:
The patent makes the existing panel capacitor serve multiple functions: it acts as both the display capacitor and the measurement capacitor. By utilizing the panel capacitor's inherent voltage characteristics during normal operation cycles, the system performs capacitance measurement without requiring separate dedicated measurement capacitors or complex external circuitry, thus maintaining low device complexity while improving measurement sensitivity.
Solution Approach 2:
The patent implements a feedback mechanism where the ADC converts the panel capacitor's voltage back to a capacitance value, which is then used by the control circuit to adjust switching timing and optimize measurement accuracy. This feedback loop enables the system to adapt to different capacitance values and maintain high sensitivity for detecting small capacitance variations caused by touch input.
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 design enhances sensitivity and reduces energy consumption by accurately measuring capacitance variations, allowing for more precise touch detection and navigation signals in electronic devices.
Implementation Method 1
a first end of the first switch is coupled to a first reference voltage, and a second end of the first switch is coupled to the panel capacitor. The second switch is turned on/off based on a voltage level of the second phase signal. A first end of the second switch is coupled to the panel capacitor.
Data Source
AI summary
A touch panel has a panel capacitor, a first capacitor, and a second capacitor. The panel capacitor and the first capacitor are charged and discharged cyclically according to a first phase signal and a second phase signal, such that an input voltage associated with the panel capacitor and the first capacitor is applied to a control circuit. The control circuit charges and discharges a second capacitor based on the input voltage and a reference voltage to compensate the difference between the input voltage and the reference voltage. The capacitance of the panel capacitor could be calculated based on the frequency of charging and discharging the second capacitor.