Contactless Communication Circuit with Capacitance Switching
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Solution Overview
Problem
Incorporating both RFID card and RFID reader/writer functions into a compact portable terminal, such as a portable telephone, poses challenges due to antenna coupling with the metallic body and each other, leading to shifted resonant frequencies and phase shifts that affect communication performance, especially in ASK modulation schemes, making it difficult to achieve optimal communication characteristics for both functions.
Innovation Solution
A contactless communication circuit with a capacitor section and capacitance switching section that forms a parallel-resonant circuit with the antenna, allowing the capacitance to be adjusted based on the function mode, either enhancing or reducing it to optimize resonant frequencies for RFID card or RFID reader/writer operations, using field-effect transistors and a control section to switch between modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If both RFID card and RFID reader/writer functions are incorporated into a compact portable terminal, then the terminal achieves multi-functionality and versatility, but antenna coupling with metal housing and each other causes resonant frequency shifts and phase issues that deteriorate communication performance
Solution Approach 1:
The patent applies dynamics by making the resonant frequency adjustable rather than fixed. A frequency adjustment section dynamically changes the resonant frequency of the antenna system depending on the operating mode (RFID card or reader/writer) and environmental conditions, allowing the system to adapt to frequency shifts caused by metal coupling and maintain reliable communication performance.
Solution Approach 2:
The patent changes the resonant frequency parameter of the antenna system to resolve the contradiction. By adjusting the resonant frequency away from shifted values caused by metal coupling, the system maintains optimal communication performance while incorporating both RFID functions in a compact terminal.
2Volume of moving object
If the antenna is arranged adjacent to metal within the housing to save space, then the terminal achieves compactness, but coupling with the metallic body shifts resonant frequencies and causes phase cancellation that deteriorates communication performance
Solution Approach 1:
The system dynamically adjusts the resonant frequency to compensate for the adverse effects of placing the antenna adjacent to metal. The frequency adjustment section detects or determines the appropriate frequency that avoids cancellation points caused by metal coupling, allowing compact antenna placement without sacrificing communication reliability.
Solution Approach 2:
The patent converts the harmful effect of metal coupling (which causes frequency shifts) into a manageable parameter by actively adjusting the resonant frequency. Instead of avoiding metal proximity, the system embraces the compact layout and compensates for the frequency shifts through dynamic adjustment, turning a potential disadvantage into an acceptable design.
3Volume of moving object
If the antenna of the RFID card and the antenna of the RFID reader/writer are disposed close to each other to save space, then the terminal achieves compactness, but coupling between antennas causes resonant frequency shifts and phase cancellation that deteriorates communication performance
Solution Approach 1:
The system dynamically adjusts the resonant frequency to account for coupling effects between the RFID card antenna and reader/writer antenna. By making the frequency adjustable, the system can optimize performance for each function while maintaining compact antenna proximity, avoiding the need to separate antennas and increase terminal size.
4Reliability
If resonant frequencies are adjusted for optimal communication distance in one function, then communication distance is improved, but the other function experiences frequency mismatch and performance degradation
Solution Approach 1:
The frequency adjustment section enables dynamic switching between different resonant frequency settings depending on which function is active (RFID card or reader/writer). This allows each function to operate at its optimal frequency for maximum communication distance while maintaining compatibility across both functions through mode-dependent frequency selection.
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 allows for satisfactory performance of both RFID card and RFID reader/writer functions by adjusting resonant frequencies, reducing design restrictions and mechanical constraints, and ensuring reliable communication by avoiding null points and optimizing communication distance.
Implementation Method 1
a capacitor section and a capacitance switching section, wherein the capacitor section forms a parallel-resonant circuit with a contactless communication antenna
Implementation Method 2
loop antennas for implementing wireless communication by electromagnetic induction are needed
Implementation Method 3
the capacitance switching section that makes a capacitance of the capacitor section effective in a mode of the contactless communication card function, and reduces the capacitance of the capacitor section in a mode of the contactless communication reader/writer function
Data Source
AI summary
The present invention provides a contactless communication circuit having both a contactless communication card function and a contactless communication reader/writer function, which includes a capacitor section that forms a parallel-resonant circuit with a contactless communication antenna; and a capacitance switching section that makes a capacitance of the capacitor section effective in a mode of the contactless communication card function, and reduces the capacitance of the capacitor section in a mode of the contactless communication reader/writer function.