Edge-Compensating Structure for Fingerprint Sensor Uniformity
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Solution Overview
Problem
Fingerprint sensing systems, particularly small capacitive sensors, face challenges in achieving uniform image quality due to edge effects caused by parasitic capacitances, which affect the accuracy of fingerprint patterns.
Innovation Solution
Incorporating an electrically conductive edge-compensating structure outside the sensor array, with synchronized time-varying voltage signals to reduce parasitic capacitances and enhance capacitive coupling uniformity across the sensor array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a small capacitive sensor array is used, then size and power consumption are reduced, but edge effects from parasitic capacitances degrade image quality and measurement precision
Solution Approach 1:
The patent introduces edge-compensating structures as intermediary elements positioned between the finger and the sensor array edges. These structures act as mediators that control the electric field distribution, preventing parasitic capacitances from degrading the measurement precision of the fingerprint image while maintaining the compact sensor size.
Solution Approach 2:
The patent modifies the electrical parameters (voltage potentials) of the edge-compensating structures to actively control and uniformize the electric field across the sensor array. By adjusting these parameters, the system compensates for edge effects and maintains high measurement precision in a small-form-factor sensor.
2Manufacturing precision
If edge-compensating structures are added, then uniformity of electric field and fingerprint image quality improve, but device complexity increases
Solution Approach 1:
The patent divides the sensor system into distinct functional segments: the central sensor array for fingerprint detection and the peripheral edge-compensating structures for field uniformization. This segmentation allows each part to perform its specific function optimally without unnecessarily increasing overall device complexity.
Solution Approach 2:
The edge-compensating structures serve multiple functions: they control parasitic capacitances, uniformize the electric field, and improve fingerprint image quality simultaneously. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
3Measurement precision
If edge-compensating structures are placed close to the sensor array (less than 0.5 mm), then edge effects are reduced, but available space and layout flexibility are constrained
Solution Approach 1:
The patent positions edge-compensating structures in the spatial dimension adjacent to the sensor array edges (less than 0.5 mm distance), utilizing the available lateral space efficiently. This dimensional placement optimizes edge effect reduction while minimizing the impact on overall layout space requirements.
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 edge effects, improving the quality of fingerprint images by maintaining consistent potential differences between sensing structures and edge-compensating structures, thus enhancing the overall performance of small fingerprint sensors without adding significant cost or real estate.
Implementation Method 1
read-out circuitry connected to each of the sensing structures for providing sensing signals indicative of a capacitive coupling between the sensing structures and the finger
Implementation Method 2
edge effects caused by parasitic capacitances, which affect the accuracy of fingerprint patterns
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
A fingerprint sensing system (3) for sensing a fingerprint pattern of a finger (26), comprising: a sensor array (7) including a plurality of electrically conductive sensing structures (10); read-out circuitry (39) connected to each of the sensing structures (10) for providing sensing signals indicative of a capacitive coupling between the sensing structures (10) and the finger (26); first signal providing circuitry (49) for providing a first time-varying voltage signal (V1(t)) to at least a portion of the sensor array (7); at least one electrically conductive edge-compensating structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) arranged outside the sensor array (7); and second signal providing circuitry (63; 65) for providing a second time-varying voltage signal (V2(t)) to the at least one edge-compensating structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83).