Capacitance Detection Circuit With Multi-Step Baseline Cancellation
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Solution Overview
Problem
Flexible capacitive touchscreens face challenges in self-capacitance detection due to high baseline capacitance, leading to small capacitance variations that are easily overwhelmed by noise, requiring large chip areas and high costs for baseline cancellation.
Innovation Solution
A capacitance detection circuit with a control module, charge transfer module, drive module, and cancellation module that performs M times of charge cancellations to generate an output voltage, allowing for efficient cancellation of baseline capacitance with a smaller cancellation capacitor, reducing noise and chip size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If on-going baseline capacitance cancellation is performed using existing self-capacitance detection technology, then the baseline capacitance can be canceled, but a huge capacitor is required resulting in large chip area and high costs
Solution Approach 1:
The patent segments the baseline capacitance cancellation process into multiple discrete steps (first baseline capacitance cancellation step and second baseline capacitance cancellation step). This segmentation allows the use of smaller cancellation capacitors in each step rather than requiring one huge capacitor, thereby reducing the overall chip area while still achieving complete baseline capacitance cancellation.
Solution Approach 2:
The patent implements periodic action by performing baseline capacitance cancellation in multiple periodic steps rather than in a single continuous operation. The detection process includes alternating between detection steps and cancellation steps, where cancellation is performed periodically at different stages. This periodic approach enables the use of smaller capacitors that can be charged and discharged repeatedly, reducing the required chip area compared to a single large capacitor.
2Measurement precision
If on-going baseline capacitance cancellation is performed, then the baseline capacitance can be canceled, but costs increase due to requiring dozens or hundreds of channels
Solution Approach 1:
The patent applies universality by designing a multi-functional detection electrode that can serve both as a detection electrode and as a cancellation electrode. This dual-functionality eliminates the need for separate dedicated cancellation electrodes and channels, reducing the total number of channels required and thereby lowering manufacturing costs while maintaining effective baseline capacitance cancellation.
3Length of moving object
If flexible screen thickness is reduced, then the screen becomes more flexible, but the baseline capacitance increases significantly making detection difficult
Solution Approach 1:
The patent applies preliminary anti-action by performing baseline capacitance cancellation before the actual touch detection process. The system proactively compensates for the large baseline capacitance caused by thin screen structure through preliminary cancellation operations, thereby eliminating the adverse effect of high baseline capacitance on detection sensitivity and enabling accurate detection of small capacitance variations despite the reduced screen thickness.
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 improves cancellation efficiency, reduces the required capacitance of the cancellation capacitor, lowers costs, and enhances detection sensitivity by effectively canceling large baseline capacitances in flexible screens.
Implementation Method 1
a drive module 122, configured to charge a capacitor CX to be detected
Implementation Method 2
a cancellation module 132, configured to charge a cancellation capacitor CC and perform M times of charge cancellations on the capacitor CX to be detected
Data Source
AI summary
The present disclosure relates to the field of touch technologies, and in particular, to a capacitance detection circuit, a capacitance detection method, a touch chip, and an electronic device. The capacitance detection circuit includes: a control module, a charge transfer module, a processing module, a drive module, and a cancellation module. The control module is configured to control the drive module to charge a capacitor to be detected. The cancellation module is configured to perform M times of charge cancellations on the capacitor to be detected. The charge transfer module is configured to convert a charge of the capacitor to be detected, subject to the M times of charge cancellations, to generate an output voltage. The processing module is configured to determine, according to the output voltage, a capacitance variation of the capacitor to be detected.