Fingerprint Sensor Impedance Variation Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current fingerprint identification technologies face challenges in simplifying the circuit structure while maintaining accuracy and responding speed, particularly in fingerprint sensors used in personal devices.
Innovation Solution
The fingerprint sensor employs first to third switches, a capacitor, an impedance variation element, and a sensing circuit that adjusts impedance based on the vertical distance from the skin surface, allowing for the identification of valley lines and ridge lines through changes in impedance value, thereby simplifying the circuit structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical sensing technology or temperature sensing technology is used to improve fingerprint identification accuracy, then the resolution and accuracy of fingerprint identification are improved, but the circuit structure becomes more complex
Solution Approach 1:
The patent changes the sensing parameter from optical or temperature detection to impedance-based detection. The sensing electrode's impedance varies with the distance to the skin surface, allowing fingerprint identification through impedance measurements rather than complex optical or temperature sensing circuits
Solution Approach 2:
The patent replaces optical sensing mechanisms or temperature sensing mechanisms with an electrical impedance-based sensing mechanism. This substitution simplifies the circuit structure by using basic electrical components (electrodes, capacitors, switches) instead of complex optical or thermal sensing systems
2Measurement precision
If traditional fingerprint sensing circuits are used to ensure accuracy, then fingerprint identification accuracy is maintained, but the responding speed decreases
Solution Approach 1:
The patent implements a pre-charge phase before the actual sensing measurement. The first switch charges the first capacitor in advance, and the second switch prepares the impedance variation element, allowing the sensing circuit to respond more quickly during the actual fingerprint detection phase without compromising measurement accuracy
3Device complexity
If a simplified circuit structure is implemented to reduce complexity, then the circuit structure is simplified, but the accuracy and responding speed may be compromised
Solution Approach 1:
The patent uses dynamic switching control with multiple switches that operate in different phases (pre-charge phase and sensing phase). The first switch controls capacitor charging, the second switch controls impedance element connection, and the third switch controls sensing signal transmission. This dynamic operation allows a simple circuit structure to achieve accurate and fast fingerprint identification
Solution Approach 2:
The patent divides the sensing process into distinct phases controlled by different switches: pre-charge phase (first switch), impedance preparation phase (second switch), and sensing phase (third switch). This segmentation allows each circuit component to perform its function optimally while keeping the overall circuit structure 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
This approach enables accurate identification of fingerprint features with improved responding speed by determining discharge time and voltage levels, enhancing the sensor's accuracy and circuit efficiency.
Implementation Method 1
an impedance value of the impedance variation element is changed according to a vertical distance between the impedance variation element and a skin surface
Implementation Method 2
the impedance variation element in the fingerprint sensor of the exemplary embodiment of the disclosure may change or adjust the impedance value of the impedance variation element according to the vertical distance between the impedance variation element and the skin surface on the finger of the user, thereby determining a discharge time between the first capacitor and the impedance variation element
Data Source
AI summary
A fingerprint sensing panel and a fingerprint sensor thereof are provided. The fingerprint sensor includes first to third switches, a first capacitor, an impedance variation element and a sensing circuit. The first switch receives a system high voltage and is controlled by a pre-charge signal. The first capacitor is coupled between the first switch and a reference voltage. The impedance variation element is coupled between the first switch and the reference voltage, and an impedance value of the impedance variation element is changed according to a vertical distance between the impedance variation element and a skin surface. The second switch receives the system high voltage. The third switch receives a read signal. The sensing circuit is coupled to the third switch and provides a fingerprint determination voltage.