Signal Processing Circuit for Electrostatic Touch Sensor
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Solution Overview
Problem
Conventional electrostatic capacitor type touch sensors struggle to distinguish multiple touch points simultaneously, as they output similar detection signals when multiple points are touched, making it difficult to accurately detect and differentiate between them.
Innovation Solution
A signal processing circuit that includes a drive circuit for alternating drive voltage, a multiplexer for selecting sense lines, and a charge amplifier to output voltage differences between capacitances, enabling differential capacitance detection and enhancing noise resistance by canceling out noise signals between adjacent sense lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitance detection is used for touch sensor, then simple detection is achieved, but multiple touch points cannot be distinguished
Solution Approach 1:
The invention segments the detection function by separating drive lines from sense lines, with drive lines generating alternating voltage and sense lines detecting capacitance changes. This segmentation enables differential measurement between multiple touch points by comparing capacitance values across different sense lines connected to the same drive line.
Solution Approach 2:
The invention changes the detection parameter from simple capacitance value to capacitance difference between adjacent sense lines. By measuring the difference in capacitance changes between multiple sense lines connected to the same drive line, the system can distinguish multiple touch points even when they produce similar absolute capacitance values.
2Measurement precision
If multiple sense lines are used for detection, then more touch points can be detected, but noise resistance decreases
Solution Approach 1:
The invention uses feedback by comparing capacitance measurements from multiple sense lines against each other. The differential measurement approach provides inherent noise rejection because common-mode noise affecting both sense lines equally is canceled out when the difference is calculated, while genuine touch signals produce differential changes.
Solution Approach 2:
The invention creates an asymmetric measurement approach where one sense line measures the actual capacitance change while another serves as a reference. This asymmetric configuration allows the system to distinguish between genuine touch signals (which create differential changes) and noise (which affects both lines similarly).
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 allows for accurate detection and differentiation of multiple touch points on a touch panel by outputting distinct voltages for each touch position, effectively distinguishing between touched points and enhancing noise resistance.
Implementation Method 1
a charge amplifier outputting an output voltage corresponding to a difference between a first capacitance and a second capacitance, where the first capacitance is detected between the first sense line selected by the multiplexer and the drive line selected by the drive circuit
Implementation Method 2
a drive circuit selecting one of the drive lines and supplying an alternating drive voltage to the selected drive line
Data Source
AI summary
The invention realizes certainly detecting two or more positions on a touch panel that are touched at the same time. A drive circuit selects one from X lines, and supplies an alternating drive voltage to the selected line. A multiplexer selects a first sense line and a second sense line from Y lines that extend to cross the X lines. A charge amplifier outputs an output voltage corresponding to a difference between a first capacitance between the first sense line and the X line selected by the drive circuit and a second capacitance between the second sense line and the X line selected by the drive circuit. A touch position is then detected based on the output voltage of the charge amplifier.