RFID Tag Coupling Circuit Using UART Interface
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Solution Overview
Problem
Existing RFID tags that use ASICs are costly due to high development and production costs, making it economically unfeasible to produce them in large quantities, and there is a need for a simple, low-power, and economical system for communication using the ISO 14443B protocol without requiring ASIC development.
Innovation Solution
An RFID tag design utilizing a microcontroller with integrated UART interface, coupled with a basic oscillating circuit and discrete components like diodes, capacitors, and transistors to facilitate communication according to the ISO 14443B protocol, allowing for data exchange and power efficiency through inductive coupling without the need for an ASIC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If an ASIC is used to produce the electronic circuit of the tag, then the size of the tag is greatly reduced, but the development and production costs increase significantly
Solution Approach 1:
The patent segments the RFID tag circuit into two parts: a reusable standard UART interface (available in common microcontrollers) and a custom RF coupling layer. This allows the bulk of the processing to be handled by off-the-shelf components while only the critical RF interface requires custom implementation, reducing overall complexity and cost.
Solution Approach 2:
The patent uses a universal UART interface that is already integrated into most microcontrollers, making the solution applicable to a wide range of existing devices. This universal interface handles the complex protocol management while the custom coupling layer adapts to RFID-specific requirements, combining the benefits of standardization and customization.
2Ease of manufacture
If discrete components are used instead of an ASIC, then the development cost is reduced, but the size and complexity of the circuit increase
Solution Approach 1:
The patent merges the UART interface functionality directly into the microcontroller unit, eliminating the need for separate discrete components for serial communication. This integration significantly reduces the number of external components required while maintaining the ability to implement the ISO 14443B protocol through software.
Solution Approach 2:
The patent introduces a coupling device as an intermediary layer between the standard UART interface and the RFID oscillating circuit. This coupling device translates between the standard serial protocol and the RFID-specific signaling requirements, allowing the use of simple discrete components without increasing overall system complexity.
3Use of energy by moving object
If a passive tag design is used without internal power supply, then the tag size is reduced and power consumption is minimized, but the power transfer efficiency may be affected
Solution Approach 1:
The patent implements dynamic power management by allowing the microcontroller to enter low-power sleep modes when not actively communicating, and to adjust its operational state based on the communication requirements. This dynamic approach minimizes power consumption while maintaining reliable operation during active data transfer.
Solution Approach 2:
The patent optimizes power transfer efficiency by carefully selecting and adjusting parameters such as the oscillation frequency (13.56 MHz carrier with 212/424/848 kHz subcarriers), modulation depth, and duty cycle of the coupling transistor. These parameter optimizations ensure efficient power transfer from the reader to the passive tag while maintaining protocol compliance.
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 enables cost-effective, low-power communication between RFID tags and read/write stations, reducing power consumption and enabling faster data transfer with improved range and speed, while eliminating the need for ASIC development, thus lowering production costs.
Implementation Method 1
The read/write station and the tag have an antenna formed by an oscillating circuit in which an electromagnetic field can be created which allows communication by magnetic coupling (also called inductive coupling)
Implementation Method 2
the demodulator 20 notably comprises a diode 21 in series between the oscillating circuit 50 and the Rx input of the UART interface
Implementation Method 3
a logic gate 40 performing an XOR (exclusive OR) logic function between two input signals
Implementation Method 4
The switching element can also be an MOS transistor, for example. Modulator 30 may also include other components such as a protection diode
Data Source
Figure 1
AI summary
The tag has a coupling device with an amplitude demodulator (20) comprising an input and an output respectively connected to an oscillating circuit (50) and to an input (Rx) of a universal asynchronous receiver/transmitter interface (15). A synchronization flip-flop (45) has an input (D) connected to an output (Tx) of the interface. An exclusive OR gate (40) has an input connected to an output (Q) of the flip-flop. An amplitude modulator (30) has an input and an output respectively connected to an output (41) of the gate and the circuit.