Capacitance Detection Circuit Virtual Ground Offset
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Solution Overview
Problem
Capacitance touch control systems face challenges with low sensitivity and accuracy due to high base capacitance and small capacitance variations in flexible screens, leading to detection circuit saturation and noise interference.
Innovation Solution
A capacitance detection circuit incorporating a control module, charge transfer module, processing module, and offsetting module to charge and offset detection capacitors, generating an output voltage that enhances capacitance variation detection and sensitivity by reducing base capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the detection electrode is placed nearer to the system ground to reduce screen thickness, then the base capacitance increases, but the capacitance variation becomes very small making detection difficult
Solution Approach 1:
The patent extracts and removes the base capacitance component from the detection capacitor by connecting it to a virtual ground through the switching circuit and operational amplifier. This separation allows the detection circuit to measure only the capacitance variation caused by touch, eliminating the interference from the large base capacitance value.
Solution Approach 2:
The patent changes the operating parameters of the detection circuit by dynamically adjusting the virtual ground potential and using programmable gain amplification. This allows the circuit to adapt to the high base capacitance condition while maintaining sensitivity to small capacitance variations, resolving the contradiction between thick screen and detection precision.
2Measurement precision
If a high circuit gain is used to detect small capacitance variation, then detection sensitivity improves, but the detection circuit tends to saturate due to high base capacitance
Solution Approach 1:
The patent extracts the base capacitance from the measurement path by routing it to a virtual ground, leaving only the capacitance variation to be amplified by the high-gain circuit. This prevents saturation while maintaining detection sensitivity, as the amplifier now processes only the small signal component without the large DC offset from base capacitance.
Solution Approach 2:
The patent introduces a virtual ground as an intermediary element between the detection capacitor and the amplification stage. This virtual ground acts as a reference point that absorbs the base capacitance effect, allowing the subsequent high-gain amplifier to operate linearly without saturation while still detecting small capacitance variations accurately.
3Volume of moving object
If self-capacitance detection is used with flexible screens, then the detection electrode can be nearer to ground, but the sensing area becomes relatively small reducing capacitance variation
Solution Approach 1:
The patent replaces the mechanical approach of increasing physical sensing area with an electrical solution using virtual ground and signal processing. By using operational amplifiers and switching circuits to create a virtual ground, the system can detect small capacitance variations from small sensing areas without being constrained by physical size limitations.
Solution Approach 2:
The patent changes the electrical parameters of the detection system by adjusting the virtual ground potential and using programmable gain amplification. This allows the circuit to maximize detection sensitivity for the available small sensing area, compensating for the reduced capacitance variation caused by the small electrode area on thin flexible screens.
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
Improves the sensitivity and accuracy of self-capacitance detection by eliminating or reducing base capacitance, allowing for more precise capacitance variation measurement and enhanced touch control performance.
Implementation Method 1
a capacitor will be formed between a detection electrode and system ground, which is known as the self-capacitance detection
Implementation Method 2
the control module is configured to charge a detection capacitor by controlling the driving module
Implementation Method 3
the offsetting module is configured to charge an offset capacitor, and control the offset capacitor to perform charge offsetting on the detection capacitor
Implementation Method 4
the charge transfer module is configured to convert charge of the detection capacitor after the charge offsetting to generate an output voltage
Data Source
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AI summary
Embodiments of the present disclosure provide a circuit, touch chip, and electronic device for capacitance detection, the circuit for capacitance detection comprising: a control module, a charge transfer module, a processing module, a driving module, and an offsetting module, the control module being configured to charge a detection capacitor by controlling the driving module, the offsetting module being configured to charge an offset capacitor, and control the offset capacitor to perform charge offsetting on the detection capacitor; the charge transfer module being configured to convert charge of the detection capacitor after the charge offsetting to generate an output voltage; and the processing module being configured to determine, based on the output voltage, a capacitance variation of the detection capacitor before and after the detection capacitor is affected by an external electric field. When the circuit is applied to self-capacitance detection, base capacitance of a detected detection capacitor may be eliminated or reduced by charge offsetting, thereby improving the capacitance variation rate and enhancing the sensitivity of the self-capacitance detection in a circumstance where the capacitance variation remains unchanged, and finally improving the accuracy of the self-capacitance detection.