Fingerprint Sensor Phase Sampling for Fake Finger Detection
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Solution Overview
Problem
Conventional capacitive fingerprint sensors are unable to effectively distinguish between a real finger and a fake finger, such as one made of conductive rubber, during the fingerprint verification process.
Innovation Solution
A fingerprint sensor device and method that applies a driving signal through a driving electrode and samples it using a fingerprint sensing plate with multiple sensing electrodes, taking readings at different phases to calculate a difference value, which is then used by a determination circuit to differentiate between a real and fake finger based on resistance and capacitance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional capacitive fingerprint sensor is used to capture fingerprint images, then the fingerprint verification function can be provided, but the sensor is incapable of effectively determining whether the contacting object is a real finger or a fake finger
Solution Approach 1:
The patent changes the parameter being measured from simple capacitance to the time-dependent characteristics of capacitance change. By measuring how capacitance evolves over time during different phases of a driving signal cycle, the system can distinguish between real fingers and fake fingers based on their different temporal response characteristics, even though both may have similar static capacitance values.
Solution Approach 2:
The patent transitions from static capacitance measurement to dynamic capacitance measurement. By applying a driving signal and measuring capacitance changes over time (during rising edge, falling edge, and different phases), the system captures the dynamic response characteristics of the contacted object, which differ between real and fake fingers due to their different physical properties.
2Measurement precision
If the reading circuit samples the driving signal at multiple different phases to obtain sampling results and calculate difference values, then the ability to distinguish real and fake fingers is improved, but the device complexity increases
Solution Approach 1:
The patent makes the existing reading circuit multi-functional by enabling it to perform multiple sampling operations at different phases using the same hardware components. The reading circuit samples capacitance at various phases (e.g., first phase, second phase, third phase) during the driving signal cycle, and the determination circuit processes these multiple samples to calculate difference values, thereby achieving enhanced authentication precision without adding separate dedicated sampling circuits for each phase.
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
Effectively differentiates between real and fake fingers by analyzing the resistance and capacitance delay phenomena in the driving signal, enhancing the security of fingerprint verification systems.
Implementation Method 1
checking the difference value to determine whether the object to be sensed is a real finger or a fake finger based on resistance and capacitance delay phenomena
Implementation Method 2
The capacitive fingerprint sensor reads the driving signal transmitted from the finger
Data Source
AI summary
A fingerprint sensor device and an operation method thereof are provided. The fingerprint sensor device includes a driving electrode, a driving circuit, a fingerprint sensing plate, a reading circuit and a determination circuit. The driving circuit applies a driving signal to an object through the driving electrode. The fingerprint sensing plate has sensing electrodes configured to sense the object. The reading circuit reads the driving signal through the fingerprint sensing plate. During a period between a rising edge time point and its adjacent falling edge time point of the driving signal, the reading circuit respectively samples the driving signal in at least two different phases to obtain at least two sampling results and outputs a difference value of the at least two sampling results. The determination circuit checks the difference value to determine whether the object to be sensed is a real finger or a fake finger.