Fingerprint Identification Parasitic Capacitance Reduction
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Solution Overview
Problem
Capacitive fingerprint identification devices are prone to inaccuracies due to the influence of parasitic capacitors in the environment, which affects the small capacitor differences formed between sensing electrodes and finger ridges and valleys, leading to low accuracy in fingerprint recognition.
Innovation Solution
The implementation of a fingerprint identification device that transmits a reference signal through an impedance element to a reading line, with adjacent signal lines also receiving the signal, synchronizing signal levels and reducing the impact of parasitic capacitors by surrounding the reading line with signal lines in different metal layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If capacitive sensing electrodes are used for fingerprint identification, then the device size and cost are reduced, but the measurement precision deteriorates due to small capacitor differences being affected by parasitic capacitors
Solution Approach 1:
The patent applies equipotentiality by connecting adjacent signal lines to the same reference potential through impedance elements. This creates equipotential regions around the reading line, causing parasitic capacitors to experience synchronous voltage changes on both sides, thereby eliminating their differential impact on the measurement signal and improving fingerprint identification accuracy while maintaining the simple capacitive sensing structure
2Ease of manufacture
If simple capacitive sensing is used, then the device cost is reduced, but the reliability deteriorates due to susceptibility to environmental parasitic capacitors
Solution Approach 1:
The patent introduces impedance elements as intermediary components connected between adjacent signal lines and the reference potential. These intermediaries actively manage the electrical environment by creating controlled potential relationships, mediating the interaction between the sensing electrodes and parasitic capacitors, thereby improving reliability without adding complex shielding or filtering structures that would increase cost
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 enhances the accuracy of fingerprint identification by minimizing the influence of parasitic capacitors, allowing for clearer differentiation between fingerprint ridges and valleys, thereby improving the overall recognition process.
Implementation Method 1
uses the capacitor difference, which the sensing electrodes form with respect to ridges and valleys on the finger surface, to obtain a fingerprint image
Implementation Method 2
transmits a reference signal to a reading line through an impedance element
Data Source
AI summary
A fingerprint identification device includes a sensing array, a reading line, a first signal source, and first to third signal lines. The reading line is disposed in a first metal layer and is electrically connected to a sensing electrode. The first signal source generates a reference signal and is connected to the reading line through an impedance element. The sensing electrode and the impedance element generate a sensing signal in response to the reference signal. The first and second signal lines are disposed in the first metal layer. The third signal line is disposed in a second metal layer. The reading line is disposed between the first and second signal lines. An orthogonal projection of the reading line on the second metal layer overlaps an orthogonal projection of the third signal line on the second metal layer. The first to third signal lines receive the reference signal.