Touch Detection Circuit With Parasitic Capacitance Cancellation
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Solution Overview
Problem
Self-capacitance type touch detection circuits face challenges in distinguishing between touch and parasitic capacitance, leading to reduced dynamic range and inability to detect two-point touches, while mutual-capacitance types are more resistant to water but less sensitive.
Innovation Solution
A self-capacitance type touch detection circuit with N first terminals, a second terminal, N first capacitance detection circuits, and a cancelling circuit that drives the second terminal to follow the voltage of the first terminal, allowing for the generation of detection signals that cancel parasitic capacitance and enhance sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If self-capacitance type detection is used, then sensitivity to touch and approach detection is improved, but the ability to detect multi-point touch and resistance to water interference deteriorates
Solution Approach 1:
The touch panel is segmented into multiple independent detection channels, each with its own sensing electrode and capacitance detection circuit. This allows simultaneous detection of multiple touch points while maintaining high sensitivity in each channel, resolving the contradiction between sensitivity and multi-point detection capability.
2Measurement precision
If mask area is reduced to decrease parasitic capacitance, then dynamic range of electrostatic capacitance measurement is improved, but noise blocking capability deteriorates
Solution Approach 1:
A buffer circuit is introduced as an intermediary between the sensing electrode and the capacitance detection circuit. The buffer maintains constant electric potential difference across the parasitic capacitance, preventing charge movement that would otherwise arise from voltage variations. This allows the mask to maintain its noise-blocking function while the system achieves improved dynamic range through parasitic capacitance compensation.
Solution Approach 2:
The parasitic capacitance, which was previously a harmful factor limiting dynamic range, is converted into a beneficial element. By using the buffer to maintain constant voltage across the parasitic capacitance, the system eliminates unwanted charge movement while still utilizing the capacitive coupling for signal detection, effectively turning the parasitic effect into a useful component of the detection mechanism.
3Measurement precision
If parasitic capacitance compensation is implemented, then dynamic range and sensitivity are improved, but circuit complexity increases
Solution Approach 1:
The buffer circuit automatically maintains constant electric potential difference across the parasitic capacitance through its inherent voltage follower configuration. This self-regulating mechanism eliminates the need for additional active compensation circuits or complex control logic, achieving parasitic capacitance compensation while keeping the overall circuit structure relatively simple.
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 effectively cancels parasitic capacitance, enabling high-sensitivity detection of electrostatic capacitance and supporting multi-point touch recognition while maintaining resistance to water interference.
Implementation Method 1
N first capacitance detection circuits corresponding to the N first terminals, changing voltages of the first terminals, respectively, and generating first detection signals indicating electrostatic capacitances of the first electrodes in accordance with movement of a charge produced in the corresponding first terminal
Implementation Method 2
a cancelling circuit, driving the second terminal in a manner that a voltage of the second terminal follows a voltage of the first terminal
Data Source
AI summary
The present disclosure provides a touch detection circuit which comes with additional, new functions, an input device and an electronic apparatus.N first terminals (Ps) are each connected with a corresponding first electrode (Es). A second terminal (Pc) is connected with a second electrode (Ec). N first capacitance detection circuits (210) correspond to the N first terminals (Ps), change voltages of the first terminals (Ps), respectively, and each generate a first detection signal indicating an electrostatic capacitance of the corresponding first electrode (Es) in accordance with movement of a charge produced in the corresponding first terminal (Ps). A cancelling circuit (240) driving the second terminal (Pc) in a manner that a voltage of the second terminal (Pc) follows a voltage of the first terminal (Ps). A second capacitance detection circuit (260) generating a second detection signal indicating an electrostatic capacitance of the second electrode (Ec).