Capacitive Touch Signal Circuit Offset Adjustment
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Solution Overview
Problem
Conventional electrostatic capacity type touch sensors are prone to malfunction due to voltage variations caused by noise, which affects the accuracy of touch detection.
Innovation Solution
A signal processing circuit that includes a first alternating current power supply, an electric charge amplifier, and an offset adjustment circuit, utilizing an excitation pad between touch pads to generate output voltages corresponding to capacitance differences and adjust for offset voltages, thereby improving noise immunity and detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional electrostatic capacity type touch sensor uses a constant current power supply to charge the touch pad, then the touch detection function is achieved, but the voltage at the touch pad varies causing malfunctioning when noise is applied
Solution Approach 1:
The patent introduces an excitation pad as an intermediary element disposed between the first and second touch pads. This excitation pad serves as a mediator that generates excitation signals to both touch pads simultaneously, allowing the system to detect capacitance changes while canceling out common-mode noise voltages. The excitation pad acts as a reference that enables differential measurement, thereby maintaining reliability in noisy environments.
Solution Approach 2:
The patent changes the operating parameter from direct voltage measurement to capacitance difference measurement. By measuring the difference in capacitance between the first and second touch pads relative to the excitation pad, the system can detect touch events while being immune to common-mode voltage variations caused by noise. This parameter transformation from voltage to capacitance differential eliminates the malfunctioning issue.
2Measurement precision
If the touch pad voltage is used for touch detection, then the touch position can be detected, but noise causes voltage variations that lead to malfunctioning
Solution Approach 1:
The patent implements a feedback mechanism where the output signal from the differential amplifier is fed back through the offset adjustment circuit to compensate for offset voltages and noise effects. The system continuously monitors the differential capacitance signal and adjusts the offset to maintain accurate touch position detection despite noise interference, thereby improving measurement precision.
Solution Approach 2:
The excitation pad serves as a mediator that enables differential measurement. By using the excitation pad as a common reference for both touch pads, the system can subtract common-mode noise voltages from the measurement, thereby improving touch position detection accuracy in noisy environments.
3Reliability
If an excitation pad is introduced between touch pads for differential measurement, then noise immunity is improved, but device complexity increases
Solution Approach 1:
The patent segments the touch panel into multiple independent capacitive elements (first touch pad, second touch pad, and excitation pad). Each segment can be independently controlled and measured, allowing differential measurement that cancels noise. This segmentation approach improves noise immunity while keeping each individual element simple in structure.
Solution Approach 2:
The excitation pad serves multiple functions: it acts as a reference electrode for differential measurement, provides excitation signals to both touch pads, and enables noise cancellation. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving improved noise immunity.
4Measurement precision
If offset voltages are not compensated, then the circuit operation is simple, but measurement accuracy deteriorates due to offset in output voltage
Solution Approach 1:
The offset adjustment circuit implements feedback by continuously monitoring the output voltage of the differential amplifier and adjusting the offset compensation signal to cancel out any DC offset or drift. This feedback mechanism improves measurement precision by eliminating offset voltages that would otherwise degrade accuracy, while using a relatively simple circuit implementation.
Solution Approach 2:
The offset adjustment circuit performs self-calibration by automatically detecting and compensating for its own offset voltages. This self-service capability improves measurement accuracy without requiring complex external calibration equipment or procedures, thereby limiting the increase in overall device complexity.
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 noise immunity and accuracy of touch position detection by compensating for offset voltages and varying capacitances, allowing for reliable operation despite noise interference and arbitrary patterning of touch pads.
Implementation Method 1
a first alternating current power supply generating a first alternating voltage
Implementation Method 2
an electric charge amplifier generating an output voltage corresponding to a difference between a first capacitance of a first capacitor and a second capacitance of a second capacitor when the first alternating voltage is applied to the excitation pad. The first capacitor is formed between the first touch pad and the excitation pad, and the second capacitor is formed between the second touch pad and the excitation pad
Implementation Method 3
The signal processing circuit also includes an offset adjustment circuit adjusting an offset in the output voltage of the electric charge amplifier
Data Source
AI summary
There is offered a signal processing circuit for an electrostatic capacity type touch sensor which can improve the noise tolerance and adjust an offset in the output voltage. The signal processing circuit for the touch sensor is structured to include an alternating current power supply providing an excitation pad with an alternating voltage, an electric charge amplifier generating an output voltage Vout corresponding to a difference between a capacitance of a first capacitor formed between a first touch pad and the excitation pad and a capacitance of a second capacitor formed between a second touch pad and the excitation pad, and an offset adjustment circuit to adjust an offset in the output voltage Vout of the electric charge amplifier.