Capacitive Fingerprint Sensor Circuit Without a Metal Ring
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Solution Overview
Problem
Capacitive fingerprint identification sensors require a metal ring that necessitates a hole in the terminal device, limiting design aesthetics and increasing signal attenuation due to equivalent capacitances formed by the device and human body, which degrades fingerprint image clarity.
Innovation Solution
A capacitive fingerprint identification sensor using a high-speed transistor and energy storage capacitor forms a power supply circuit, with a conversion circuit modulating the driving signal to eliminate the need for a metal ring, enhancing signal coupling and clarity by forming a loop between the finger and device ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal ring is used to drive the capacitive sensor, then the sensor can detect fingerprint capacitance variations, but the device structure becomes complex and requires a hole in the screen
Solution Approach 1:
The patent extracts and eliminates the metal ring component from the system. Instead of using an external metal ring for driving the capacitive sensor, the invention integrates the driving function directly into the sensor structure, removing the need for the metal ring and its associated hole in the screen, thus simplifying the overall device structure while maintaining fingerprint detection capability
Solution Approach 2:
The patent merges the driving function with the sensor unit by integrating the driving electrode array directly into the sensor structure. This combination eliminates the need for separate metal ring components and external connections, reducing structural complexity while preserving the capacitive coupling mechanism necessary for fingerprint detection
2Reliability
If a metal ring is used to enlarge capacitance CT, then signal attenuation is reduced, but the device appearance is compromised and waterproof performance deteriorates
Solution Approach 1:
The invention removes the metal ring component that caused appearance compromise and waterproof issues. By extracting this external component and integrating the driving function directly into the sensor, the patent maintains signal coupling strength through the integrated electrode array while preserving the device's appearance integrity and waterproof performance
Solution Approach 2:
The patent nests the driving electrode array within the sensor unit structure itself, eliminating the need for external metal ring components. This nested integration allows the driving function to be embedded within the existing device structure, maintaining both signal coupling and appearance integrity without requiring separate external components
3Device complexity
If the sensor unit is integrated without a metal ring, then the device structure is simplified, but the driving signal may suffer from attenuation due to equivalent capacitances
Solution Approach 1:
The patent merges the driving electrode array with the sensor unit to create an integrated structure. This integration maintains strong signal coupling by reducing the distance and impedance between driving and sensing elements, compensating for the removal of the external metal ring while preserving signal strength and simplifying the overall structure
Solution Approach 2:
The invention changes the electrical parameters of the driving system by using an integrated electrode array with optimized capacitance values. By adjusting the capacitance parameters of the integrated structure, the patent maintains adequate signal coupling strength while eliminating the need for external metal ring components
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 solution broadens the application scope of fingerprint sensors, maintains design integrity, and improves fingerprint identification effectiveness by reducing signal attenuation and enhancing image clarity.
Implementation Method 1
the capacitance Cx between ridges and valleys of fingerprints in different zones and the capacitor induction units 102 varies, and the capacitor induction units 102 detects that the voltage varies accordingly
Implementation Method 2
a conversion circuit modulating a driving signal output by the sensor unit to drive a sensor ground of the sensor unit
Data Source
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AI summary
Disclosed is a fingerprint identification sensor, which comprises: a sensor unit, comprising a capacitor array formed by a plurality of capacitor induction units and having an output, a power supply and a sensor ground output; a conversion circuit, connected to the device ground of the terminal device, and the output and the sensor ground of the sensor unit, and configured to, upon modulating the driving signal to the modulated signal, output the modulated signal to the sensor ground; an energy storage capacitor, connected between the power supply and the sensor ground, and configured to stabilize an operating voltage of the sensor unit; a high-speed transistor switch, connected to the power supply, and configured to perform synchronous switch-on and switch-off according to status of the conversion circuit power supply; and a power supply, connected to the conversion circuit and the power supply of the sensor unit via the high-speed transistor switch.