Fingerprint Sensor Layout With Shielding Against Parasitic Capacitance
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Solution Overview
Problem
Fingerprint sensing devices face interference from parasitic capacitances, which affect the quality of fingerprint detection.
Innovation Solution
The implementation of a fingerprint sensing device with a shielding layer between sensing pads and data lines, along with a control circuit that alternately applies sensing and auxiliary voltages to reduce interference and enhance charge storage for improved sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If data lines are placed close to sensing pads for compact design, then device area is reduced, but parasitic capacitance increases causing sensing interference
Solution Approach 1:
A shielding layer is introduced as an intermediary component between the data lines and sensing pads. This shielding layer acts as a mediator that blocks the harmful electromagnetic coupling and parasitic capacitance from forming between adjacent data lines and sensing pads, while allowing the compact layout to be maintained.
Solution Approach 2:
The harmful parasitic capacitance effect is extracted and isolated by introducing the shielding layer, which separates the data lines from the sensing pads electrically. This extraction removes the interference pathway while preserving the compact physical layout.
2Measurement precision
If sensing voltage is continuously applied to sensing pads, then fingerprint detection is maintained, but charge leakage through data lines reduces sensing accuracy
Solution Approach 1:
Instead of continuously applying sensing voltage, the patent uses periodic alternating voltage application. The control circuit alternates between applying sensing voltage to one row of sensing pads and auxiliary voltage to adjacent rows, creating a time-varying pattern that prevents continuous charge leakage paths while maintaining detection capability.
Solution Approach 2:
The voltage application pattern is made dynamic through the control circuit that alternates between different sensing pads rows. This dynamic switching prevents stable charge leakage paths from forming, as the voltage potentials are constantly changing rather than static.
3Object-affected harmful factors
If shielding layer is added between sensing pads and data lines, then parasitic capacitance interference is reduced, but device complexity increases
Solution Approach 1:
The shielding layer is designed to serve multiple functions: it provides electromagnetic shielding between data lines and sensing pads, acts as a reference potential plane, and works in conjunction with the control circuit to enable the alternating voltage pattern. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The shielding layer is merged with the existing data line structure and sensing pad array, forming an integrated multi-layer configuration. Rather than adding separate shielding structures, the design combines the shielding function with the existing signal transmission architecture.
4Measurement precision
If auxiliary voltage lines are added to provide alternating voltages, then charge storage capability is improved, but manufacturing complexity increases
Solution Approach 1:
The auxiliary voltage lines are designed to serve dual purposes: they provide the alternating voltage pattern needed for reduced charge leakage, and they can also function as additional sensing elements or reference structures. This multi-functionality justifies the additional manufacturing steps.
Solution Approach 2:
The voltage application is segmented into different rows with different voltage patterns. The control circuit divides the sensing pad array into multiple rows and applies different voltage patterns to each row sequentially, enabling the alternating voltage scheme without requiring complete redesign of the entire sensing structure.
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 configuration reduces interference and increases the sensitivity of fingerprint detection by allowing sufficient charge storage on sensing pads, enabling better identification of fingerprint peaks and valleys.
Implementation Method 1
A typical capacitive type fingerprint sensing device can include a plurality of sensing pads. The fingerprint sensing device can detect the fingerprint by detecting the capacitance formed between the finger and the sensing pads.
Implementation Method 2
However, there are parasitic capacitances in the fingerprint sensing device, so that the sensation of fingerprint may be affect. The shielding layer is disposed between the sensing pads and the data lines.
Data Source
AI summary
A fingerprint sensing device comprises a plurality of sensing pads, a plurality of data lines, a shielding layer, and a plurality of auxiliary voltage lines. The data lines are separately and electrically connected to the sensing pads, and configured to provide a sensing voltage to the sensing pads. The shielding layer is disposed between the sensing pad and the data lines. The auxiliary voltage lines are separately and electrically connected to the sensing pads, configured to provide an auxiliary voltage to the sensing pads. The auxiliary voltage is different from the sensing voltage. When a first sensing pad receives the sensing voltage, a second sensing pad adjacent to the first sensing pad receives the auxiliary voltage.