Fingerprint Sensor Drive Grouping for Accurate Mutual Capacitance Sensing
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Solution Overview
Problem
Current fingerprint sensing devices lack the necessary high resolution and sensitivity to accurately detect fingerprint patterns, leading to decreased sensitivity and accuracy in authentication processes.
Innovation Solution
A fingerprint sensor design featuring a touchpad with intersecting driving and sensing electrodes, where driving electrodes are grouped and signals are applied sequentially, allowing for the measurement of electrical signals and calculation of mutual capacitance with different weights based on node location, enhancing sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If driving electrodes are divided into multiple driving groups and signals are applied sequentially, then sensitivity and accuracy of fingerprint detection are improved, but device complexity and measurement time increase
Solution Approach 1:
The driving electrodes are divided into multiple driving groups (first driving group, second driving group, etc.) that are sequentially activated. This segmentation allows the system to measure mutual capacitance at different node sets in separate time steps, improving measurement precision by reducing crosstalk and enabling weighted averaging of measurements, while the complexity is managed through systematic control of the driver unit.
Solution Approach 2:
The driver unit applies driving signals to different driving groups in a periodic, sequential manner. The first driving group is activated during a first time period, the second driving group during a second time period, and so on. This periodic activation pattern enables precise temporal control of capacitance measurements at different node sets, improving fingerprint detection accuracy through time-multiplexed measurement.
2Measurement precision
If different weights are assigned to mutual capacitance measurements based on node location, then fingerprint detection accuracy is improved, but processing complexity increases
Solution Approach 1:
Different weights are assigned to mutual capacitance measurements based on the location of nodes within the touchpad. Nodes at different positions (e.g., center vs. edge) receive different weighting factors in the fingerprint pattern calculation. This local quality approach improves measurement accuracy by accounting for position-dependent variations in capacitance characteristics, while the processor manages the complexity through systematic weight application.
3Measurement precision
If the activated area is expanded through electrode grouping, then sensitivity is improved, but measurement time increases
Solution Approach 1:
Multiple driving electrodes are grouped into driving groups that are activated simultaneously within each time period. The first driving group contains multiple driving electrodes activated together, as does the second driving group. This merging of electrodes within groups expands the activated area and improves sensitivity, while the sequential activation of different groups manages the overall measurement time.
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 increases the sensitivity and accuracy of fingerprint detection by expanding the activated area and properly weighting mutual capacitance measurements, resulting in improved fingerprint recognition capabilities.
Implementation Method 1
a signal measurement unit configured to measure electrical signals generated from the plurality of sensing electrodes in response to the driving signal
Implementation Method 2
electrical signals generated from the plurality of sensing electrodes in response to the driving signal
Data Source
AI summary
Sensing sensitivity of a fingerprint sensor may be enhanced by grouping driving electrodes and driving groups. A processor of the fingerprint sensor may calculate mutual capacitance at each node on a touchpad from gross mutual capacitances in areas including a plurality of channels.