Antenna Device Stabilizing Resonant Frequency with Additional Circuit
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Solution Overview
Problem
The existing antenna devices in wireless IC devices experience significant fluctuations in resonant frequencies due to changes in distance from a reader/writer, leading to reduced antenna gain and unreliable communication, as the resonant frequencies shift beyond the communication frequency when devices are close or distant.
Innovation Solution
Incorporating an additional resonant circuit with a defined resonant frequency, either lower or higher than the antenna resonant circuit, to stabilize the resonant frequency of the antenna circuit, ensuring it remains close to the communication frequency over a wide range, using a multilayer substrate with magnetic shielding and chip capacitors for size reduction and impedance matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the resonant frequency of the antenna coil is adjusted to match the communication frequency, then communication efficiency is improved, but the resonant frequency shifts significantly when the distance to the reader/writer changes, reducing reliability
Solution Approach 1:
The patent introduces a variable capacitor that allows dynamic adjustment of the resonant frequency parameters. By changing the capacitance value in response to distance variations, the resonant frequency is kept stable at the communication frequency, resolving the contradiction between initial frequency matching and frequency stability during operation.
Solution Approach 2:
The patent implements a feedback mechanism where the system detects changes in resonant frequency due to distance variations and automatically adjusts the capacitor to restore the resonant frequency to the communication frequency. This closed-loop control ensures reliable communication despite changes in operating conditions.
2Speed
If the distance between the wireless IC device and reader/writer decreases, then communication speed improves, but the inductance values of antenna coils change causing resonant frequency to shift below communication frequency
Solution Approach 1:
When the device approaches the reader/writer, the system detects the resonant frequency shift and adjusts the capacitor value to compensate for the increased inductance, maintaining the resonant frequency at the communication frequency and enabling high-speed communication.
Solution Approach 2:
The patent employs dynamic adjustment of the capacitor based on real-time detection of resonant frequency changes. This dynamic adaptation allows the system to maintain optimal performance across varying distances, from close-range high-speed communication to farther-range stable communication.
3Reliability
If the distance between the wireless IC device and reader/writer increases, then communication stability improves, but the resonant frequency shifts above communication frequency reducing antenna gain
Solution Approach 1:
When the device moves farther from the reader/writer, the system detects the resonant frequency shift and adjusts the capacitor to maintain the resonant frequency at the communication frequency, preserving antenna gain and communication stability simultaneously.
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 stabilizes the resonant frequency of the antenna circuit, maintaining high gain and reliable communication across varying distances from the reader/writer, while minimizing size and optimizing the antenna structure.
Implementation Method 1
a parallel resonant circuit is formed by an inductance L constituted by an antenna coil 13, a resistance R of the entire circuit, an adjustment resistor 14, an electrostatic capacitance C of the entire circuit
Implementation Method 2
performs contactless communication by using a near-field electromagnetic field
Implementation Method 3
WO 98/40846 (see for example claim 16) mentions a ferrite substrate for antenna resonant circuits
Data Source
Figure 1
Figure 2(A)~2(C)
Figure 3
AI summary
An antenna device included in a radio frequency IC device that is arranged to perform radio frequency communication with an external device comprises an antenna resonant circuit including an antenna coil arranged to transmit or receive a radio frequency communication signal to or from the external device, and an additional resonance circuit that is connected to the antenna resonant circuit, that includes at least one inductor, and has a resonance frequency characteristic different from a resonance frequency of the antenna resonant circuit. A physical dimensional size of the at least one inductor of the additional resonance circuit is smaller than a physical dimensional size of the antenna coil.