Fingerprint Sensing Apparatus with Capacitance-Shielding Wires
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional capacitive fingerprint sensors face challenges with noise interference from data lines, leading to reduced sensing accuracy due to crosstalk and self-capacitance issues, especially in thin protective glass configurations used in frameless smartphones.
Innovation Solution
The implementation of a fingerprint sensing apparatus with first and second capacitance-shielding wires that sandwich the data lines, receiving a capacitance-eliminating signal to reduce interference and enhance sensing accuracy by eliminating crosstalk and self-capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional capacitive sensing is used with long data lines, then the sensing area can be large, but crosstalk and noise interference increase significantly
Solution Approach 1:
A ground shielding layer is introduced as an intermediary between adjacent data lines to block electromagnetic interference and crosstalk. The shielding layer acts as a mediator that prevents harmful electromagnetic fields from coupling between neighboring signal lines, thereby reducing noise while preserving the large sensing area capability
2Device complexity
If data lines are placed close to sensing electrodes, then routing complexity is reduced, but self-capacitance and noise sensing increase
Solution Approach 1:
A ground shielding layer is positioned between the data lines and sensing electrodes to act as an electromagnetic barrier. This intermediary structure allows simplified routing while preventing the data lines from directly coupling with sensing electrodes, thereby reducing self-capacitance effects and noise interference that would degrade measurement precision
3Length of stationary object
If protective glass thickness is reduced to hundreds of micrometers, then the device becomes more compact and economical, but the sensing signal becomes minute and more susceptible to interference
Solution Approach 1:
A ground shielding layer is introduced beneath the thin protective glass structure to provide electromagnetic protection. This intermediary shielding layer compensates for the reduced signal strength caused by the thin glass thickness by blocking external noise and interference, thereby maintaining measurement precision despite the compact design
4Object-affected harmful factors
If conventional ground connection is used to block noise, then noise blocking is achieved, but considerable self-capacitance is induced that vanishes the sensing signal
Solution Approach 1:
Instead of directly grounding the data lines (which creates large self-capacitance), a ground shielding layer is introduced as an intermediary structure. This shielding layer provides noise blocking functionality while being positioned and configured to minimize direct capacitive coupling with the signal paths, thereby preventing the sensing signal from being overwhelmed by self-capacitance effects
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 configuration significantly improves the accuracy of fingerprint sensing by minimizing noise interference, allowing for more precise detection of fingerprint capacitance signals while maintaining the economic benefits of capacitive sensors.
Implementation Method 1
a first capacitance-shielding wire and a second capacitance-shielding wire being provided for a corresponding data line in the plurality of data lines and sandwiching the corresponding data line
Data Source
AI summary
A fingerprint sensing apparatus includes a plurality of fingerprint sensing electrodes, a plurality of data lines respectively sandwiched by a first capacitance-shielding wire and a second capacitance-shielding wire, a fingerprint sensing circuit including a driver circuit with a gain larger than zero or equal to zero. During fingerprint sensing, the fingerprint sensing circuit sends a capacitance-exciting signal to a selected fingerprint sensing electrode, receiving a fingerprint sensing signal from the selected fingerprint sensing electrode, processing the fingerprint sensing signal with the driver circuit into a capacitance-eliminating signal and applying the capacitance-eliminating signal to the first capacitance-shielding wire and the second capacitance-shielding wire respectively. The capacitance between the first/second capacitance-shielding wire and the corresponding data line can be greatly reduced because the voltages at the first/second capacitance-shielding wire have same phase as that of corresponding data line, thus greatly enhance the accuracy of the fingerprint sensing apparatus.