Delta Modulator Receive Channel for Dual-Mode Capacitance Sensing
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Solution Overview
Problem
Capacitance sensing systems face challenges in accurately distinguishing between mutual and self capacitance, particularly in touch panels, which affects the reliability of touch event detection and user interface performance under varying conditions.
Innovation Solution
A capacitance measurement system that can switch between mutual and self capacitance sensing modes, utilizing a delta modulator receive channel with multiplexers, transimpedance amplifiers, and negative feedback loops to convert capacitance changes into digital values, allowing for synchronized drive and receive operations and improved noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a capacitance sensing system uses a single sensing mode (either mutual or self capacitance), then the circuit design is simpler, but the system cannot accurately distinguish between both types of capacitance under varying conditions
Solution Approach 1:
The system dynamically switches between mutual capacitance sensing mode and self capacitance sensing mode based on operational requirements. The capacitance sensing circuit is configured to operate in mutual capacitance mode during mutual capacitance measurement and in self capacitance mode during self capacitance measurement, allowing adaptive response to different sensing needs without permanent structural changes
Solution Approach 2:
The capacitance sensing circuit is designed to perform multiple functions by sensing both mutual capacitance and self capacitance using the same hardware infrastructure. The system can detect mutual capacitance between transmit and receive electrodes and self capacitance of individual electrodes, making the circuit universal for different capacitance measurement requirements
2Measurement precision
If the system measures both mutual and self capacitance separately, then touch event detection accuracy improves, but the measurement time and processing complexity increase
Solution Approach 1:
The system performs mutual capacitance measurement and self capacitance measurement in periodic alternating fashion. During first time periods, the circuit measures mutual capacitance between transmit and receive electrodes. During second time periods, the circuit measures self capacitance of electrodes. This periodic switching allows both measurement types to be conducted systematically without requiring simultaneous measurement
Solution Approach 2:
The system performs compensation measurements preliminarily to establish baseline capacitance values before actual touch detection. Compensation waveforms are generated and stored in advance to compensate for parasitic capacitances and environmental factors, enabling more accurate touch event detection during subsequent measurement periods
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
Enhances the accuracy and reliability of touch event detection by effectively measuring both mutual and self capacitance, improving user interface performance and noise resistance in capacitive touch panels.
Implementation Method 1
a transimpedance amplifier configured to convert the received current into a voltage
Implementation Method 2
a delta modulator configured to modulate the voltage into a digital value
Implementation Method 3
Capacitance sensing systems can sense electrical signals generated on electrodes that reflect changes in capacitance
Implementation Method 4
When a conductive object (e.g., a finger, hand, or other object) comes into contact or close proximity with a capacitive sense element, the capacitance changes and the conductive object is detected
Data Source
AI summary
A circuit, system, and method for measuring capacitance are described. A current may be received at an input of a conversion circuit. The current may be converted to a voltage signal which may be used to create a negative feedback current to the input of the conversion circuit and which may be demodulated digitally to provide a static digital output representative of a capacitance.