Dual Optical Capacitive Sensor for Low-Power Fingerprint Detection
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Solution Overview
Problem
Existing input devices face challenges in efficiently detecting the presence of input objects, such as fingers, in low-power modes, as optical sensing methods consume significant power and are not effective in low-power conditions.
Innovation Solution
The integration of a dual optical and capacitive sensor system, where capacitive sensing is used to detect the presence of input objects during low-power states, switching to optical sensing for fingerprint capture when necessary, utilizing a photosensor and a capacitive sensing layer with sensor electrodes to drive constant or AC signals for detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical sensing is used to detect the presence of a finger, then detection accuracy is improved, but power consumption increases significantly
Solution Approach 1:
The system dynamically switches between capacitive sensing mode (for presence detection in low-power state) and optical sensing mode (for fingerprint capture when finger is detected). The sensor operates in different modes depending on the operational state, transitioning from capacitive field-based detection to optical imaging only when necessary
Solution Approach 2:
The sensor performs capacitive sensing periodically to detect finger presence, and only activates optical sensing when a finger is detected. This periodic alternation between low-power capacitive mode and higher-power optical mode reduces overall energy consumption while maintaining detection capability
2Reliability
If optical sensing is used in low-power mode, then fingerprint capture capability is maintained, but the device cannot effectively operate in low-power state
Solution Approach 1:
The sensing functionality is segmented into two separate mechanisms: capacitive sensing for presence detection and optical sensing for fingerprint capture. Each segment serves its specific purpose, allowing the system to use only the capacitive segment during low-power mode for presence detection, reserving the optical segment for when actually needed
3Use of energy by moving object
If capacitive sensing is integrated with optical sensor, then power consumption is reduced, but device complexity increases
Solution Approach 1:
The patent combines capacitive sensing electrodes and optical sensing elements into a single integrated sensor structure. The capacitive sensing layer is formed over the optical sensor array, allowing both sensing mechanisms to coexist in one device footprint, sharing common structural elements and reducing overall system complexity despite the dual functionality
Solution Approach 2:
The integrated sensor serves multiple functions: capacitive sensing for presence detection, optical sensing for fingerprint capture, and the same structure supports both low-power and full-power operational modes. This multi-functionality reduces the need for separate dedicated 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 approach reduces power consumption by using capacitive sensing in low-power modes and effectively captures fingerprints using optical sensing when needed, enhancing usability and efficiency.
Implementation Method 1
the input device may include a fingerprint sensor that uses optical sensing to detect ridges and valleys in a finger
Implementation Method 2
the sensing region includes sensor electrodes used to measure changes in capacitance resulting from an input object (e.g., a finger or stylus) interacting with the sensing region
Data Source
AI summary
Embodiments herein provide a dual optical and capacitance sensor. During a first time period, the dual sensor uses optical sensing to capture a fingerprint (e.g., to identify or verify the fingerprint). During a second time period, the dual sensor uses one or more capacitive sensor electrodes to perform capacitive sensing. The capacitive sensing may be absolute capacitive sensing or transcapacitive sensing.