Fingerprint Sensor Outdoor Imaging via Modulated Backlight Filtering

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Solution Overview

Problem

Existing image acquiring apparatuses struggle to capture fingerprint images outdoors due to the influence of external light, particularly sunlight, as they are not designed to exclude or mitigate the effects of reflected light.

Innovation Solution

An image acquiring apparatus is developed with a light irradiation unit that modulates light with a specific frequency band, combined with a matrix of photosensors and signal processing units, including a band pass filter and low pass filter, to isolate and remove DC components caused by external light, allowing for effective imaging of objects like fingerprints even in outdoor conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a fingerprint sensor using a photosensor is integrated into a display, then the display can capture fingerprint images, but the apparatus cannot capture images outdoors due to external light interference

Engineering Contradiction:

Improveoutdoor imaging capabilityVSAvoidexternal light influence

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The backlight is modulated to emit light at a specific frequency (e.g., 100 Hz), creating periodic light emission. The photosensor detects this modulated light, and the signal processing unit extracts the fingerprint image signal at the same frequency. This periodic action allows the system to distinguish between the modulated backlight signal and external ambient light, enabling outdoor imaging capability while rejecting external light interference.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The signal processing unit uses the known modulation frequency of the backlight to selectively amplify and extract the fingerprint image signal from the photosensor output. By providing feedback based on the modulation frequency, the system can filter out external light components that do not match this frequency, thereby resolving the contradiction between capturing images outdoors and rejecting external light influence.

Inventive Principle:

Principle #23Feedback

2Adaptability or versatility

If the backlight drive circuit is modified to modulate light frequency, then outdoor imaging becomes possible, but the device complexity increases

Engineering Contradiction:

Improveoutdoor imaging capabilityVSAvoidcircuit modification complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The backlight drive circuit is designed to perform multiple functions: it drives the backlight for normal display operation and simultaneously modulates the backlight at a specific frequency for fingerprint imaging. By making the backlight drive circuit multi-functional, the system achieves outdoor imaging capability without adding separate dedicated circuitry, thus minimizing the increase in device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The fingerprint imaging function is merged with the existing display backlight drive circuit. The modulation signal generation and light emission control are combined in a single integrated circuit, eliminating the need for separate complex imaging circuits. This merging approach enables outdoor imaging while keeping the overall device complexity low.

Inventive Principle:

Principle #5Merging (Combining)

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 enables the apparatus to capture clear images of objects, such as fingerprints, by filtering out the impact of external light, thereby allowing for reliable imaging outdoors without significant modifications to the existing backlight drive circuit.

Implementation Method 1

a light irradiation unit configured to be capable of radiating light modulated with a modulation signal in a predetermined frequency band

Methodology Applied

Scientific EffectLight modulation: Phase Modulation

Implementation Method 2

photosensors configured to be capable of receiving the light radiated from the light irradiation unit, the light including reflected light reflected by an object

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 3

a generation unit configured to generate a DC component from an electrical signal output from the photosensor due to the light received by the photosensor on the basis of the predetermined frequency band or the modulation signal

Methodology Applied

Scientific EffectSignal filtering: Filter (electronic)

Data Source

PatentUS11495045B2Image acquiring apparatus and display apparatus equipped therewith

Publication Date: 2022.11.08 CONNECTEC JAPAN CORP

AI summary

An image acquiring apparatus includes: a light irradiation unit configured to be capable of radiating light modulated with a modulation signal in a predetermined frequency band; photosensors configured to be capable of receiving the light radiated from the light irradiation unit, the light including reflected light reflected by an object, and the photosensors being arranged in a matrix; and a generation unit configured to generate a DC component from an electrical signal output from the photosensor due to the light received by the photosensor on the basis of the predetermined frequency band or the modulation signal.