Optical Biometric Sensor with Ambient Light Control
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Solution Overview
Problem
Conventional capacitive fingerprint sensors struggle to detect fine ridge and valley features through thick layers, such as smartphone cover glass, and optical sensors are too bulky for mobile devices, while being sensitive to ambient lighting conditions.
Innovation Solution
An optical imaging device with an array of sensing elements and a control circuit that adjusts gain and exposure based on ambient light conditions, using masked sensing elements with spatial light blocking masks to prevent saturation and allow for effective imaging in bright light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical sensors are used for fingerprint imaging, then imaging capability through thick layers is improved, but device size becomes too bulky for mobile devices
Solution Approach 1:
The patent applies local quality by creating a localized optical imaging path through a light guide structure. The light guide is positioned only in the specific region where fingerprint imaging is needed, allowing optical sensing capabilities in a localized area without making the entire device bulky. This enables the system to have optical sensing properties where needed while maintaining a compact overall form factor suitable for mobile devices.
2Reliability
If conventional optical sensors are used, then imaging through thick cover glass is improved, but the sensor becomes sensitive to ambient lighting conditions
Solution Approach 1:
The patent implements preliminary anti-action by using spatial light blocking masks that are pre-configured to block ambient light before it reaches the sensing elements. These masks are positioned in the optical path to prevent harmful ambient light from saturating the sensors, thereby counteracting the adverse effect of ambient lighting conditions before they can interfere with fingerprint imaging.
Solution Approach 2:
The patent converts the harmful effect of ambient light into a beneficial selective filtering process. By using spatial light blocking masks with specific aperture patterns, the system allows only certain light paths (from the fingerprint) to reach the sensors while blocking ambient light. This transforms the challenge of ambient light sensitivity into an opportunity for enhanced selective imaging capability.
3Reliability
If spatial light blocking masks are added to prevent saturation, then performance in bright light is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the light guide structure to serve multiple functions simultaneously. The light guide not only directs light for fingerprint imaging but also integrates the spatial light blocking masks into its structure. This multi-functional design allows the system to achieve bright light performance enhancement without adding separate, complex components, as the light guide itself becomes the carrier for both illumination and light blocking functions.
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
Enables reliable imaging of biometric inputs, like fingerprints, through thick layers without the need for mechanical cutouts and maintains performance across varying lighting conditions, reducing power consumption and latency.
Implementation Method 1
a first spatial light blocking mask configured to allow a first amount of light to reach a sensing area of the first sensing element
Implementation Method 2
an optical sensor array including a plurality of unmasked sensing elements, the plurality of unmasked sensing elements being configured to image an input object
Data Source
AI summary
An optical imaging device for imaging a biometric input object is provided. The optical imaging device includes an optical sensor having an array of sensing elements. The optical sensor is configured to first read a first subset of sensing elements in the array of sensing elements; analyze the first read of the first subset of sensing elements to determine an ambient light condition; first alter an operating point of the optical imaging device based on the ambient light condition; and image the input object.