Fingerprint Sensor Finger Lost Detection Circuit
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Solution Overview
Problem
Existing fingerprint sensing systems face challenges in achieving low energy consumption while accurately determining the presence of a finger and sensing fingerprint patterns, leading to potential repeated image acquisitions and inefficient power management.
Innovation Solution
The implementation of capacitive sensing elements that detect capacitive coupling between the sensing elements and a finger, with dedicated finger detecting circuitry that provides digital interrupt signals for finger presence and absence, allowing the device to transition between active and inactive states based on capacitive coupling thresholds, thereby reducing energy consumption and preventing unwanted image acquisitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fingerprint sensing device continuously operates to detect finger presence and acquire fingerprint images, then the detection accuracy and response time are improved, but the energy consumption increases significantly
Solution Approach 1:
The system dynamically transitions between inactive and active states based on finger presence detection. The control circuit adjusts the operational mode of the fingerprint sensing device in real-time, switching from a low-power inactive state to a high-performance active state only when a finger is detected, thereby optimizing the balance between detection accuracy and energy consumption.
Solution Approach 2:
The system employs periodic sampling of capacitive coupling values to detect finger presence. Instead of continuous operation, the sensing device periodically checks for finger presence and only activates full fingerprint acquisition functionality when needed, reducing overall energy consumption while maintaining reliable detection capability.
2Speed
If the fingerprint sensing device operates in active state to ensure rapid fingerprint acquisition, then the response time is reduced, but the energy consumption increases
Solution Approach 1:
The system performs preliminary detection of finger presence using capacitive sensing elements before activating the full fingerprint acquisition process. This preliminary action allows the device to prepare for rapid fingerprint acquisition only when a finger is actually present, avoiding energy waste while maintaining fast response capability when needed.
Solution Approach 2:
The sensing elements continuously monitor capacitive coupling in a low-power mode and automatically trigger the active state when finger presence is detected. This self-service mechanism eliminates the need for continuous high-power operation while ensuring rapid response when a finger is placed on the sensor.
3Use of energy by moving object
If the device remains in inactive state to minimize energy consumption, then the energy efficiency is improved, but the detection response time increases
Solution Approach 1:
The system uses periodic sampling of capacitive coupling values even in inactive state, allowing it to quickly detect finger presence and transition to active state. This periodic monitoring maintains energy efficiency while ensuring that the system can respond rapidly when a finger is placed on the sensor, minimizing the effective detection response time.
4Reliability
If the fingerprint sensing device performs repeated image acquisitions to ensure accurate fingerprint detection, then the detection reliability is improved, but the energy consumption and processing time increase
Solution Approach 1:
The system uses feedback from capacitive sensing elements to determine whether a finger is present before initiating fingerprint acquisition. This feedback mechanism allows the device to skip unnecessary acquisition attempts when no finger is detected, reducing processing time and energy consumption while maintaining reliable detection by only performing acquisitions when conditions are appropriate.
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 significantly reduces power consumption by efficiently managing the device's state transitions based on finger presence, minimizing repeated image acquisitions, and ensuring accurate fingerprint detection, thereby enhancing energy efficiency and user experience.
Implementation Method 1
each providing a measure indicative of the capacitive coupling between that particular sensing element and a finger surface touching the sensor surface
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
The present invention relates to a fingerprint sensing device comprising an array of sensing elements;readout circuitry connected to the array of sensing elements; and finger detecting circuitry for detecting if a finger candidate is touching the sensing surface of the fingerprint sensing device. The fingerprint sensing device is controllable between an active state and an inactive state. When the finger print sensing device is in the inactive state, the finger detecting circuitry is configured to provide a finger lost signal for indicating when the finger candidate no longer touches the sensing surface of the fingerprint sensing device.