Fingerprint Sensor Dynamic Capacitance Sensing
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Solution Overview
Problem
Conventional fingerprint sensors face challenges in determining and processing sensed capacitances due to limited sensing electrode area, leading to reduced signal penetration and increased manufacturing costs, especially when trying to increase the area of the transmission electrode.
Innovation Solution
A sensing method that dynamically adjusts between self-capacitance sensing and mutual capacitance sensing based on the required resolution, allowing for sequential performance of these methods to increase the area of sensing pixels, thereby enhancing signal sensitivity and reducing scan time and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the area of the sensing electrode is increased to improve signal sensitivity, then the sensing capability is enhanced, but the area available for transmission electrode is reduced, leading to increased transmission impedance and reduced signal penetration
Solution Approach 1:
The sensing electrode is divided into multiple sensing pixels arranged in an array, where each pixel can be independently controlled. This segmentation allows different regions to perform different functions (sensing vs. transmission) simultaneously, resolving the contradiction between sensing area and transmission area.
Solution Approach 2:
The patent transitions from conventional single-layer electrode design to a multi-layer electrode structure with sensing electrodes and transmission electrodes positioned at different depths. This dimensional separation enables both sensing and transmission functions to coexist without competing for the same surface area.
2Measurement precision
If the area of the sensing electrode is increased to improve signal sensitivity, then more capacitance can be sensed, but the manufacturing process becomes more complex with increased number of steps and layers
Solution Approach 1:
The sensing pixels serve multiple functions: they act as sensing electrodes for capacitance detection, transmission electrodes for signal delivery, and can be selectively activated based on identification requirements. This multi-functionality reduces the need for separate dedicated structures for each function.
Solution Approach 2:
The system dynamically adjusts the sensing mode (self-capacitance or mutual capacitance) and the number of active sensing pixels based on the identification requirements. This dynamic adaptation allows the device to optimize performance for different scenarios without requiring fixed complex structures for all possible uses.
3Measurement precision
If self-capacitance sensing is performed on all sensing pixels to achieve high resolution, then the identification accuracy is improved, but the scan time and power consumption increase
Solution Approach 1:
Instead of always activating all sensing pixels, the system selectively activates only the necessary number of pixels based on the identification requirements. When high resolution is not needed, fewer pixels are activated, reducing scan time and power consumption while maintaining sufficient identification accuracy.
Solution Approach 2:
The system periodically switches between self-capacitance sensing and mutual capacitance sensing modes, and between different numbers of active pixels, based on the current identification requirements. This periodic adaptation allows the system to optimize between resolution, speed, and power consumption for different operational scenarios.
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 allows for improved scan resolution and sensitivity while reducing scan time and power consumption, effectively addressing the limitations of conventional fingerprint sensors by dynamically adjusting sensing methods according to identification requirements.
Implementation Method 1
self-capacitance sensing is performed on the sensing pixels to provide a first fingerprint pattern
Implementation Method 2
the self-capacitance sensing and mutual capacitance sensing are performed on the sensing pixels to provide a second fingerprint pattern
Data Source
AI summary
A sensing method of a fingerprint sensor is provided. The fingerprint sensor includes a plurality of sensing pixels arranged in an array, and the sensing pixels respectively have a sensing electrode. The sensing method includes following steps. A required resolution of an identification requirement is determined; here, the identification requirement is received by the fingerprint sensor. If the number of pixels of the required resolution is less than or equal to the number of the sensing pixels, self-capacitance sensing is performed on the sensing pixels to provide a first fingerprint pattern. If the number of pixels of the required resolution is greater than the number of the sensing pixels, the self-capacitance sensing and mutual capacitance sensing are performed on the sensing pixels to provide a second fingerprint pattern.