Fingerprint Detection Circuit Virtual Ground Integration
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Solution Overview
Problem
Existing fingerprint detection technologies require a user's finger to be in contact with an external electrode for excitation signal connection, limiting their applicability to various scenarios.
Innovation Solution
A fingerprint detection circuit with a detection electrode, amplifier, and feedback capacitance that forms capacitances between the finger, detection electrode, and virtual ground, allowing all signals to be processed within a detection chip without the need for an external electrode connection, enabling fingerprint detection in more scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an external electrode is used to connect the excitation signal to the user's finger, then the fingerprint detection can be performed with existing circuit designs, but the device structure becomes more complex and the applicability is limited to scenarios where external electrodes can be connected
Solution Approach 1:
The patent merges the excitation signal generation and fingerprint detection functions into a single integrated circuit. The excitation signal is generated within the detection chip itself, eliminating the need for separate external electrodes. This integration reduces device structure complexity while expanding applicability to scenarios like under-screen fingerprint detection where external electrodes cannot be easily connected.
Solution Approach 2:
The detection electrode serves multiple functions: it acts as both the excitation signal application point and the detection electrode. By making the detection electrode multi-functional, the patent eliminates the need for separate external electrodes, simplifying the device structure while maintaining fingerprint detection capability across various application scenarios.
2Reliability
If two metal plates are required for each pixel (external electrode and detection electrode), then the excitation signal can be properly applied, but the device structure becomes more complex
Solution Approach 1:
The patent combines the excitation signal application function and detection function into a single detection electrode. The excitation signal is applied through the detection electrode itself rather than requiring a separate external electrode, thereby maintaining reliable excitation signal connection while reducing device structure complexity.
Solution Approach 2:
The detection electrode is designed to serve dual purposes: applying the excitation signal and detecting the fingerprint capacitance. This multi-functionality eliminates the need for a second metal plate (external electrode), simplifying the overall device structure while ensuring reliable signal connection.
3Reliability
If a finger must contact an external electrode for excitation signal connection, then the fingerprint detection loop can be formed, but the ease of operation is reduced and the user experience is degraded
Solution Approach 1:
By merging the excitation signal application and detection functions into the detection electrode, the patent eliminates the need for users to contact separate external electrodes. The fingerprint detection loop is formed through the integrated circuit architecture, maintaining reliability while significantly improving ease of operation as users simply need to place their finger on the normal touch surface.
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
Enables fingerprint detection without the need for external electrode contact, allowing for broader applicability, such as under screen glass in mobile terminals, by reflecting fingerprint information in capacitances and output signals within the detection chip.
Implementation Method 1
a first capacitance is formed between a finger and the detection electrode, a second capacitance is formed between the finger and a virtual ground
Data Source
AI summary
A fingerprint detection circuit includes: a detection electrode, where a first capacitance is formed between a finger and the detection electrode, a second capacitance is formed between the finger and a virtual ground, and a parasitic capacitance is formed between the detection electrode and the virtual ground; an amplifier, where an inverting input end of the amplifier is connected to the detection electrode and a non-inverting input end of the amplifier is connected to an excitation signal; and a feedback capacitance, where one end of the feedback capacitance is connected to the inverting input end of the amplifier, the other end of the feedback capacitance is connected to an output end of the amplifier, and the output end of the amplifier outputs an output signal of the fingerprint detection circuit. There is no need to connect an excitation signal to a finger of a user through an external electrode.