Fingerprint Sensor Touch Screen Capacitance Reduction
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Solution Overview
Problem
Capacitive fingerprint sensors integrated with touch screens face issues of increased mutual capacitance, which reduces sensitivity and can lead to unrecognized touch operations due to their high-density sensor patterns, complicating configuration and increasing non-display areas.
Innovation Solution
A fingerprint sensor integrated type touch screen device with a high-density electrode pattern, where the touch IC selectively connects and disconnects Rx electrode lines to reduce mutual capacitance by grouping touch sensors and floating or grounding ineffective channels, allowing for simultaneous touch and fingerprint sensing without compromising sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-density sensor array is used for fingerprint sensing, then measurement precision is improved, but mutual capacitance increases causing touch sensitivity to deteriorate
Solution Approach 1:
The sensor array is segmented into multiple groups (first group and second group) with different functions. The first group is dedicated to fingerprint sensing while the second group is dedicated to touch sensing. This segmentation allows each group to be optimized for its specific function, preventing the mutual capacitance interference that occurs when all sensors operate simultaneously for both functions.
Solution Approach 2:
The system dynamically switches between fingerprint sensing mode and touch sensing mode. During fingerprint sensing, only the first sensor group is activated while the second group is deactivated. During touch sensing, the second group is activated. This dynamic activation/deactivation resolves the conflict between high-density sensing precision and touch sensitivity by ensuring only the necessary sensors are active at any given time.
2Adaptability or versatility
If a separate fingerprint sensor assembly is used, then fingerprint recognition function is achieved, but device complexity and non-display area increase
Solution Approach 1:
The fingerprint sensor and touch sensor share the same physical sensor array structure and electrode patterns. Both functions are integrated into a single sensor system rather than using separate assemblies. The same sensor array serves dual purposes: fingerprint recognition when in fingerprint mode, and touch detection when in touch mode, thereby reducing device complexity and eliminating the need for separate fingerprint sensor assemblies.
Solution Approach 2:
The sensor array is designed with universal functionality to perform both fingerprint sensing and touch sensing. By implementing mode switching between fingerprint mode and touch mode, a single sensor system achieves multiple functions, eliminating the need for separate dedicated assemblies for each function and reducing overall device complexity.
3Measurement precision
If a push button assembly is integrated with the fingerprint sensor, then fingerprint sensing is enabled, but the sensing area is limited by the button size and thickness increases
Solution Approach 1:
The fingerprint sensing function is merged with the touch screen surface itself rather than requiring a separate push button assembly. The sensor array is integrated directly into the touch screen structure, allowing the entire touch screen area to serve as the fingerprint sensing area. This eliminates the limitation of button size and reduces overall device thickness.
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 mutual capacitance, enhances touch sensitivity, and allows for accurate fingerprint recognition within the same screen area, reducing the need for a separate fingerprint sensor area and minimizing bezel space, thereby improving user interface convenience.
Implementation Method 1
a capacitive sensor array configured to detect a touch input
Implementation Method 2
The capacitive fingerprint sensor utilizes a difference of electric charges charged between ridges and valleys of the fingerprint contacted thereto
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
Disclosed is a fingerprint sensor integrated type touch screen device that includes a touch screen having at least one fingerprint and touch area and a plurality of touch areas, each touch area including Tx electrode lines of a first group crossing Rx electrode lines of the first group, and touch sensors at crossings of the Tx electrode lines of the first group and the Rx electrode lines of the first group; and a touch integrated circuit (IC) that supplies a sensor driving signal of a same phase to the Tx electrode lines of the first group, groups first effective Rx channels of the Rx electrode lines of the first group as a bundle, and simultaneously senses the first effective Rx channels through a first touch sensing part, wherein first ineffective Rx channels of the Rx electrode lines of the first group are electrically disconnected from the first touch sensing part.