Current-Conveyor Capacitance Sensing for Noise-Resistant Touch Input
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Solution Overview
Problem
Capacitive touch sensors face challenges in noise immunity and operational mode limitations, particularly in mutual capacitance sensing, where they are sensitive to environmental noise and can only operate in single modes, affecting touch coordinate resolution and noise rejection.
Innovation Solution
The development of a capacitance sensing circuit that can operate in both self-capacitance and mutual capacitance sensing modes using a single current conveyor, with full-wave demodulation for improved noise suppression and the ability to handle both current and voltage inputs, enhancing noise rejection and touch coordinate resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage input capacitance sensing circuits are used, then high input impedance is achieved suitable for sensing via high-resistance materials, but noise immunity deteriorates as circuits become too sensitive to environmental noise
Solution Approach 1:
The capacitance sensing circuit is designed to operate in multiple operational modes (self-capacitance sensing and mutual capacitance sensing) using a single current conveyor, eliminating the need for separate circuits for different sensing modes. This multi-functionality allows the circuit to adapt between high-impedance voltage input mode and low-impedance current input mode, thereby achieving both high measurement precision for high-resistance materials and improved noise immunity when operating in current input mode.
2Object-affected harmful factors
If current input capacitance sensing circuits are used, then noise immunity is improved with low input impedance, but adaptability deteriorates as they cannot effectively sense via high-resistance materials
Solution Approach 1:
The circuit employs dynamic switching between different operational modes through control signals that activate specific circuit configurations. The circuit can dynamically transition between voltage input mode (for high-resistance material sensing) and current input mode (for noise immunity), allowing it to adapt to different sensing requirements in real-time based on the operational conditions.
3Device complexity
If single operational mode sensing circuits are used, then circuit simplicity is maintained, but measurement precision deteriorates due to limited touch coordinate resolution
Solution Approach 1:
The capacitance sensing circuit integrates multiple sensing capabilities (self-capacitance and mutual capacitance sensing) within a single unified circuit architecture using one current conveyor. This allows the circuit to select the appropriate sensing mode based on the touch interaction type, thereby improving touch coordinate resolution and measurement precision without requiring multiple separate circuits, thus maintaining relative simplicity while enhancing performance.
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 provides improved noise immunity and touch coordinate resolution by enabling operation in multiple sensing modes, effectively suppressing AC noise and improving the circuit's ability to handle high-frequency and switching power supply noise, thus enhancing the reliability of touch sensing systems.
Implementation Method 1
The transconductance circuit 410 operates in an inversion mode, converting a voltage input to a current input
Implementation Method 2
the sensor capacitor Cs is charged to a voltage VDD... the switch SW2 is turned on and the switch SW1 is turned off... the sensor capacitor Cs is discharged to the integration capacitor CINT
Data Source
AI summary
An apparatus for and a method of sensing capacitance of one or more sensor elements in multiple capacitance sensing modes, including a self-capacitance sensing mode and a mutual capacitance sensing mode.