NFC Device Symmetrical Filter Configuration for Harmonic Noise
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Solution Overview
Problem
NFC communication is often disrupted by interfering signals or noise, especially when an NFC reader is connected to a remote antenna via a cable, leading to unreliable operation due to harmonics of the base operating frequency.
Innovation Solution
The NFC device incorporates a symmetrical receive interface with first and second filter configurations placed on each line to filter out specific harmonics of the base operating frequency, using a trap filter with an LC configuration to eliminate disturbing frequencies, thereby preventing them from reaching the NFC reader.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an NFC reader is connected to a remote antenna via a cable, then the NFC device can operate with extended antenna placement flexibility, but the NFC communication becomes susceptible to interference and noise from harmonics
Solution Approach 1:
The patent divides the receive interface into two separate lines (first line and second line), each with its own filter configuration. This segmentation allows independent filtering of harmonics on each line, improving noise rejection while maintaining the connected antenna system's flexibility.
Solution Approach 2:
The patent introduces filter configurations as intermediary elements between the cable/antenna and the NFC reader processing stages. These filters act as mediators that selectively remove harmful harmonics (at frequencies n×f_base + f_subcarrier where n>2) while allowing the fundamental NFC frequency to pass through, thus protecting the communication reliability without affecting antenna placement flexibility.
2Object-affected harmful factors
If filter configurations are added to eliminate harmonics, then noise immunity is improved, but the device complexity increases
Solution Approach 1:
The patent applies filtering only at specific critical points - the receive interface lines where harmonics would most directly impact the NFC reader. By placing filters locally at the first and second lines of the symmetrical receive interface rather than throughout the entire system, the noise immunity is improved with minimal additional complexity.
Solution Approach 2:
The filter configurations are designed to target specific frequency parameters (harmonics at n×f_base + f_subcarrier where n>2) rather than broad frequency ranges. This selective parameter-based filtering achieves effective noise immunity by removing only the harmful harmonic frequencies while preserving the fundamental NFC operating frequency, avoiding the need for complex wide-band filtering.
3Reliability
If selective harmonic filtering is implemented, then communication reliability is improved, but the device complexity increases
Solution Approach 1:
The patent implements a symmetrical receive interface with balanced filter configurations on both first and second lines. This symmetrical design (rather than asymmetrical) provides common-mode noise rejection and ensures that harmonic filtering is applied equally to both signal paths, improving functional reliability while maintaining circuit balance and simplicity.
Solution Approach 2:
The filter configurations serve multiple functions simultaneously: they reject harmonics at frequencies n×f_base + f_subcarrier where n>2, they maintain the symmetrical balance of the receive interface, and they preserve signal integrity for reliable NFC communication. This multi-functionality achieves improved reliability without proportionally increasing complexity.
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 solution significantly improves noise immunity by filtering out harmonics, ensuring reliable NFC communication and reducing noise levels by more than 40dB, particularly effective for NFC readers connected to remote antennas via long coaxial cables.
Implementation Method 1
a trap filter with an LC configuration to eliminate disturbing frequencies
Implementation Method 2
The NFC communication, especially the NFC reception, may be interrupted or disturbed by an interfering signal or a noise signal
Data Source
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Figure 2
Figure 3~5
AI summary
The invention relates to an NFC device (250) and a method (400) for eliminating selectively a disturber when receiving signals at a base operating frequency, e.g., over a coaxial cable, comprising at least one filter configuration (208, 209, 210) configured to filter out a harmonic of the base operating frequency.