Capacitance detecting device for fingerprint identification and fingerprint identification apparatus comprising the same
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Solution Overview
Problem
Existing fingerprint detection technologies face challenges in accuracy due to parasitic capacitances, which affect the detection of fingerprint characteristics and introduce noise in the circuit.
Innovation Solution
A capacitance detecting device for fingerprint identification is designed with a detecting module that charges and measures the sensing capacitance and feedback capacitance, while keeping parasitic capacitances at a fixed potential, thereby eliminating their impact on the detection process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If parasitic capacitances are present in the detecting circuit, then the circuit can be simplified, but the detection accuracy is significantly reduced
Solution Approach 1:
The patent extracts and separates the parasitic capacitance from the detection circuit by introducing a dedicated compensation capacitor that is electrically connected in parallel with the sensing capacitor. This allows the parasitic capacitance to be measured and compensated independently, removing its harmful effect on detection accuracy while maintaining circuit simplicity.
Solution Approach 2:
The patent changes the electrical parameters of the circuit by introducing a compensation capacitor with a specific capacitance value that matches the parasitic capacitance. By adjusting and matching this parameter, the harmful parasitic capacitance is transformed into a compensatable element, enabling accurate fingerprint detection despite its presence in the circuit.
2Device complexity
If parasitic capacitances are present in the detecting circuit, then the circuit structure can be maintained simple, but noise is introduced and detection accuracy is reduced
Solution Approach 1:
The patent converts the harmful parasitic capacitance into a beneficial element by using it as the basis for compensation. The compensation capacitor is designed to match the parasitic capacitance value, and by measuring and compensating for this capacitance, the previously harmful noise source becomes a controllable parameter that can be eliminated from the detection signal.
3Measurement precision
If multiple conductive layers are used for fingerprint detection, then detection capability is improved, but parasitic capacitances between layers increase
Solution Approach 1:
The patent extracts the parasitic capacitance effect from the multi-layer structure by introducing a separate compensation capacitor that is electrically connected to the sensing capacitor. This allows the parasitic capacitance generated by the multiple conductive layers to be measured and compensated independently, enabling the multi-layer structure to maintain its enhanced detection capability without being degraded by inter-layer parasitic capacitance.
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 significantly enhances the accuracy of fingerprint detection, reduces circuit noise, and decreases power consumption and circuit area, leading to a more efficient fingerprint identification process.
Implementation Method 1
a sensing capacitance C f is formed between a top conductor layer and a finger
Implementation Method 2
to control electric charges of the sensing capacitance C f and electric charges of the feedback capacitance C m to transfer to the integrating capacitance C i
Data Source
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AI summary
A capacitance detecting device for fingerprint identification comprises a conductive border (200), a detecting screen (100) and a detecting module (300). The detecting screen (100) comprises a plurality of detecting units (110). Each detecting unit (110) comprises a first conductive layer (111), a second conductive layer (112), a third conductive layer (113) and a fourth conductive layer (114). The detecting module (300) is configured to charge a sensing capacitance between the first conductive layer (111) and a finger (5) in contact with the detecting screen (100) and a feedback capacitance between the first conductive layer (111) and the second conductive layer (112) at a sampling stage, to control electric charges of the sensing capacitance and the feedback capacitance to transfer to an integrating capacitance between the third conductive layer (113) and the fourth conductive layer (114) at an integral stage, to measure a voltage variation of the integrating capacitance at the integral stage and to calculate the sensing capacitance according to the voltage variation. A fingerprint identification apparatus is also provided.