Propagating Electrodes for Fingerprint Sensor Sensitivity

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Solution Overview

Problem

Capacitance-based fingerprint sensors face challenges in accurately detecting fingerprint features due to noise interference and reduced sensitivity, especially when the fingerprint is oriented at different angles, limiting their effectiveness in small form factor devices like smartphones and tablets.

Innovation Solution

The use of propagating electrodes in a fingerprint sensor pattern, which increases the change in capacitance and signal-to-noise ratio, enhancing the detection of fingerprint features by coupling with both TX and RX electrodes and improving anisotropy, thereby improving fingerprint image generation and authentication accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If conventional capacitance sensing is used in small form factor devices, then device size is reduced, but fingerprint detection sensitivity and accuracy deteriorate due to noise interference

Engineering Contradiction:

Improvedevice sizeVSAvoidfingerprint detection accuracy

Core Design Contradiction:

Volume of moving objectVSMeasurement precision

Solution Approach 1:

The sensor array is divided into multiple independently controllable electrode groups (TX and RX electrodes), allowing selective activation and localized sensing. This segmentation enables the system to maintain high detection accuracy in small form factors by focusing sensing resources on specific regions rather than requiring a large uniform sensor array.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs multiple phases of TX signals with different parameters (frequency, amplitude, timing) to excite the capacitive sensing elements. By varying these parameters across different phases and electrode combinations, the system enhances the signal-to-noise ratio and improves fingerprint detection accuracy despite the limited sensor area in small form factor devices.

Inventive Principle:

Principle #35Parameter changes

2Area of stationary object

If sensor array size is reduced for small form factor devices, then device compactness is improved, but signal-to-noise ratio deteriorates

Engineering Contradiction:

Improvesensor array areaVSAvoidnoise interference

Core Design Contradiction:

Area of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The system uses periodic multi-phase TX signals to sequentially excite different electrode combinations. This periodic action allows the system to accumulate useful capacitive signals over multiple cycles while averaging out random noise, thereby improving the signal-to-noise ratio even with a reduced sensor array area in compact devices.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The capacitance sensing system incorporates feedback mechanisms where the measured capacitance changes from RX electrodes are used to adjust and optimize subsequent sensing phases. This feedback enables the system to enhance weak fingerprint signals while suppressing noise, maintaining high detection quality despite the smaller sensor area in compact form factors.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If multi-phase TX signals are used, then fingerprint detection accuracy is improved, but system complexity increases

Engineering Contradiction:

Improvefingerprint feature detection accuracyVSAvoidsignal generation and control complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The complex multi-phase signaling is broken down into separate, independently controllable electrode groups and signal phases. Each phase and electrode combination can be controlled separately, allowing the system to achieve high detection accuracy through coordinated simple operations rather than requiring a single complex signal generation system.

Inventive Principle:

Principle #1Segmentation

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 proposed solution significantly enhances the sensitivity and accuracy of fingerprint detection, allowing for more precise fingerprint feature recognition and authentication, even with smaller sensor arrays, by increasing the useful component of the sensor signal and reducing noise interference.

Implementation Method 1

Capacitance sensing systems function by sensing electrical signals generated on electrodes that represent changes in capacitance. When a fingerprint ridge comes into contact with or is in close proximity to a sense element, the capacitance change caused by the fingerprint ridge is detected.

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

Methodology Applied

Scientific EffectElectrical signal propagation: Conduction (electrical)

Data Source

PatentUS10956703B2Fingerprint sensor pattern

Publication Date: 2021.03.23 INFINEON TECHNOLOGIES AMERICAS CORP

AI summary

An example system drives one or more transmit signals on first electrodes disposed in a first layer and propagating electrodes disposed in a second layer. The system measures a capacitance of sensors through a of second electrodes. Each second electrode crosses each first electrode to provide a plurality of discrete sensor areas, each discrete sensor area associated with a difference crossing and including a portion of at least one propagating electrode. Each second electrode is galvanically isolated from the first electrodes and the propagating electrodes.