Fingerprint Sensor Settlement Detection for Low-Power Image Capture
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Solution Overview
Problem
Existing fingerprint sensors face challenges in accurately detecting finger presence with reduced power consumption and sensitivity, especially when presence sensing electrodes are disposed under a cover layer, which can reduce signal gain and increase latency due to temperature fluctuations.
Innovation Solution
The implementation of a capacitive sensing system with signal conditioning elements in parallel to presence sensing electrodes, along with a processing system that captures multiple input object settlement scans by driving transmitter electrodes simultaneously and detecting receiver signals, determines if the difference between scans is below a threshold to acquire a full input object image efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If presence sensing electrodes are disposed under a cover layer to enable fingerprint sensing, then the sensor can detect finger presence, but signal gain is reduced and detection sensitivity decreases
Solution Approach 1:
Signal conditioning elements are introduced as intermediary components between the presence sensing electrodes and the processing system. These elements amplify and condition the weak signals generated by the electrodes under the cover layer, compensating for the signal loss caused by the cover layer's presence while maintaining accurate finger detection capability
Solution Approach 2:
The system dynamically adjusts sensing parameters such as scan frequency, integration time, and signal threshold based on detected conditions. By changing these parameters, the system optimizes the balance between detection accuracy and signal strength, compensating for the reduced gain caused by the cover layer structure
2Reliability
If the sensor continuously scans to capture fingerprint images, then image capture capability is maintained, but power consumption increases unnecessarily when no fingerprint is present
Solution Approach 1:
The system implements periodic scanning with variable intervals. Instead of continuous scanning, it performs scans at predetermined intervals when no finger is detected, and increases scan frequency only when finger presence is detected. This periodic action with adaptive timing reduces power consumption while maintaining the ability to capture fingerprints when needed
Solution Approach 2:
The presence sensing electrodes perform preliminary detection of finger presence before initiating full fingerprint image capture. This preliminary action filters out unnecessary full scans when no finger is present, significantly reducing power consumption while ensuring that image capture is triggered only when appropriate
3Measurement precision
If multiple settlement scans are captured and compared to detect finger settlement, then detection accuracy is improved, but latency increases due to temperature fluctuations and processing time
Solution Approach 1:
The system uses feedback from sequential settlement scans to dynamically adjust comparison thresholds and determine when sufficient settlement has occurred. By analyzing the feedback from each scan comparison, the system can make real-time decisions about when to proceed with image capture, reducing unnecessary waiting time while maintaining accurate settlement detection
Solution Approach 2:
The system performs a limited number of settlement scans with comparison against threshold values rather than exhaustive monitoring. By using partial action (comparing only essential scan pairs) and setting appropriate threshold criteria, the system achieves sufficient settlement detection accuracy without the excessive time cost of continuous multi-scan comparison
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 and latency while maintaining sensitivity, allowing for accurate finger presence detection and image acquisition with reduced time and energy resources.
Implementation Method 1
a capacitive sensor configured to capacitively sense an input object in proximity to a plurality of sensor electrodes
Data Source
AI summary
Low power input object settlement detection systems and methods for operating a capacitive sensor having a plurality, M, of transmitter electrodes and a plurality, N, of receiver electrodes, wherein N and M are integer values. A plurality of input object settlement scans are captured, when a presence of an input object is detected, or in response to a presence of an input object being detected, wherein capturing each input object settlement scan includes driving all or a portion of the plurality, M, of transmitter electrodes simultaneously and detecting receiver signals from at least a subset of the plurality, N, of receiver electrodes simultaneously. When a difference between subsequent input object settlement scans is below a threshold value, a full input object image is acquired.