Fingerprint Sensing Circuit Layout With Two Metal Layers
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Solution Overview
Problem
Conventional fingerprint sensing circuits require at least three metal layers for sensing electrodes, scan lines, and sensing lines, which increases costs and complexity, necessitating a reduction in metal layer count without compromising functionality.
Innovation Solution
A fingerprint sensing circuit design that incorporates sensing electrodes in a first conductive layer, a sensing line and clock signal line in a second conductive layer, and flip flops and AND gates to control switches, eliminating the need for a third conductive layer by using a parallel configuration for the sensing and clock signal lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If three metal layers are used for sensing electrodes, scan lines, and sensing lines, then the fingerprint sensing functionality is complete, but the production cost and device complexity increase
Solution Approach 1:
The patent combines the sensing line and clock signal line into the same second conductive layer, allowing them to share the same metal layer. This merging reduces the total number of metal layers from three to two while maintaining all necessary sensing functions through proper signal routing and timing control
Solution Approach 2:
The second conductive layer serves multiple functions by carrying both the sensing line signals and clock signal line signals. This multi-functional usage of the same metal layer eliminates the need for a dedicated third layer, reducing overall device complexity while preserving complete fingerprint sensing capability
2Reliability
If three metal layers are used for sensing electrodes, scan lines, and sensing lines, then the circuit functionality is complete, but the production cost increases
Solution Approach 1:
By merging the sensing line and clock signal line into the same second conductive layer, the patent reduces the total metal layer count from three to two. This reduction directly lowers production costs associated with additional metal deposition processes while maintaining complete circuit functionality through careful signal management
3Device complexity
If sensing line and clock signal line are placed in the same conductive layer, then the number of metal layers is reduced, but signal interference may occur
Solution Approach 1:
The patent uses periodic clock signals to control the timing of sensing operations. By synchronizing the switching of sensing electrodes with the clock signal periods, the system ensures that sensing lines are active only during designated time windows, preventing interference between simultaneous signals in the same conductive layer
Solution Approach 2:
The flip-flops are configured to control switches in advance based on clock signal timing. This preliminary control ensures that sensing electrodes are activated and deactivated at precise moments before potential interference can occur, allowing multiple signals to coexist in the same layer without mutual interference
Data Source
AI summary
The fingerprint sensing circuit including sensing electrodes, switches, a sensing line and flip flops. First terminals of the switches are respectively coupled to the sensing electrodes. The sensing line is coupled to second terminals of the switches. Output terminals of the flip flops are respectively coupled to control terminals of the switches. An input terminal of part of the flip flops is coupled to the output terminal of a previous flip flop.