Touch Sensor Circuit for High-Voltage Self-Capacitance Sensing
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Solution Overview
Problem
In touch sensors using self-capacitance sensing methods, the inability to employ high-voltage charging signals due to withstanding voltage limitations of touch integrated chips (ICs) hinders the generation of sensing signals with high signal-to-noise ratios (SNR).
Innovation Solution
The implementation of a touch sensor design that includes a sensor cell coupled to a sensor line, a transmitter switch for charging, and a receiver switch for sensing, utilizing a coupling capacitor and an integrator with an amplifier and analog-to-digital converter to process signals, allowing for high-voltage charging while maintaining a suitable SNR through voltage management and offset adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-voltage charging signal is used in self-capacitance sensing, then the signal-to-noise ratio of sensing signals is improved, but the withstanding voltage limitation of touch integrated chips prevents its use
Solution Approach 1:
The patent introduces a coupling capacitor as an intermediary component between the high-voltage charging signal source and the touch sensor chip. This capacitor couples the high-voltage signal to the sensor line during charging, while the sensor chip only experiences manageable voltage levels during sensing, thus mediating between the high-voltage requirement for good SNR and the low-voltage tolerance of the chip
Solution Approach 2:
The patent employs periodic switching between charging mode and sensing mode. During a first period, a high-voltage charging signal is applied to charge the sensor line; during a second period, the charging signal is removed and the sensing signal is measured. This time-division multiplexing allows the system to benefit from high-voltage charging intermittently without continuously exposing the chip to dangerous voltage levels
2Quantity of substance
If a high-voltage charging signal is applied to the sensor line, then more charge is stored in the sensor cell, but the touch integrated chip cannot withstand the high voltage
Solution Approach 1:
The coupling capacitor serves as a mediator that allows high-voltage charging to occur without directly exposing the voltage-sensitive integrated chip to high voltage. The capacitor transfers charge to the sensor line during charging periods while isolating the chip during sensing periods
Solution Approach 2:
The patent applies the charging signal in advance during a first period before the sensing period begins. This preliminary charging action stores sufficient charge in the sensor cell before measurement, ensuring that the subsequent sensing operation occurs at manageable voltage levels while still benefiting from the prior high-voltage charge injection
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 the use of high-voltage charging signals in self-capacitance sensing, enhancing the signal-to-noise ratio of sensing signals and improving touch detection accuracy in display devices.
Implementation Method 1
a coupling capacitor including a first electrode coupled to the second switch and a second electrode coupled to the sensor channel
Implementation Method 2
a sensor cell which is coupled to a sensor line and forms a self-capacitance with the cathode of the light emitting diodes
Data Source
AI summary
A touch sensor includes a sensor cell coupled to a sensor line, a sensor transmitter including a first switch coupled to the sensor line and a power supply which supplies a charging signal to the sensor line during a first period during which the first switch is turned on, and a sensor receiver including a second switch coupled to the sensor line and a sensor channel which receives a sensing signal from the sensor line during a second period during which the second switch is turned on. The sensor receiver further includes a coupling capacitor including a first electrode coupled to the second switch and a second electrode coupled to the sensor channel.