RFID Chips

January 31, 2024

Cadence PCB Solutions

Key Takeaways

RFID chips are integrated circuits inside RFID tags containing all the components of a controller, memory, and microprocessor. They carry and transmit objects’ information.
RFID chips are categorized by frequency — Low Frequency (LF), High Frequency (HF), Ultra High Frequency (UHF), and Microwave Frequency. Higher frequencies offer extended communication ranges, with the popular 13.56 MHz HF band known for near-field communication (NFC).
The architecture of an RFID chip has three main parts: Radio Frequency (RF) Transceiver, Detection Section, and Control Section.

RFID tag with a chip and an antenna

RFID chips are integrated circuits inside RFID tags. They are small, highly integrated microchips that contain a logical control unit, memory, and transceiver for decoding, decrypting, and error checking. RFID chips may be read-only, with a factory-assigned serial number that can be used as a key into a database, or have read and write capabilities. Today, technology in RFID chips has evolved to include features such as passwords, data encryption, and more.

RFID Chips Categorized by Tag Functionality: Passive, Semi-Passive and Active

Passive Systems

The most popular. Passive systems cover all frequency ranges. They derive power from the magnetic field generated when radio waves reach the chip's antenna to transmit stored information.

Semi-Passive Systems

Also known as battery-assisted passive (BAP) tags. They share the principle of passive tags but integrate a battery for extended communication range, enhanced tag memory, and in some cases, additional sensors.

Active Systems

Often operate in the UHF and microwave frequency bands. They can achieve a range of up to 100 m. There are two main types of active tags: transponders and beacons.

Transponders “wake up” when they receive a radio signal from a reader and respond by transmitting a signal back. The tag functions similarly to passive RFID systems in that it communicates with the reader upon receiving a signal. However, the key difference is its power source, enabling it to respond by sending back a signal with the necessary data when the tag enters the reader's field. This type of tag conserves battery life effectively since it remains inactive until it comes within range of a reader.
Beacons announce the presence of the tag at predetermined intervals to any reader within range of the tag. The continuous broadcasting allows these tags to be tracked over longer distances, with some capable of being detected hundreds of meters away, making them suitable for warehouses and healthcare facilities.

RFID Chip System Architecture

The RFID chip system architecture is designed to carry and transmit a unique identification seamlessly by integrating three essential components: the RF Transceiver, Detection Section, and Control Section.

RF Transceiver

The RF Transceiver consists of an antenna and an impedance-matching circuit. The antenna is designed to capture specific frequencies from the reader and transmit information. The impedance-matching circuit minimizes signal reflection between the antenna and the transponder circuit, ensuring efficient communication and data transfer. LF and HF systems communicate through inductive (magnetic) coupling, where energy transfers through a shared magnetic field. Higher frequency systems operate by backscatter (radiative) coupling using an electromagnetic field, enabling a longer read range.

Detection Section

The Detection Section has two circuits: rectifier and demodulation circuits. The rectifier circuit serves the essential function of supplying the required DC voltage to the digital circuit. Within this circuit, a limiter and voltage pump circuit either limit or increase DC power.

Simultaneously, the demodulation block decodes commands from the reader directed toward the tag. This section converts RF energy from the transceiver's antenna into a baseband signal or equivalent DC voltage through sophisticated demodulation circuitry. This transformed signal is then forwarded to the Control Section for further processing, with the DC voltage providing the power supply.

Control Section

The Control Section incorporates analog and digital signal processing subsections, a protocol detection circuit, an encryption circuit, and memory.

RFID Chip Communication Steps to Transceiver

Step	Component	Function
1	Reception of RF Signal	The initial step where the RF signal is received.
2	Demodulation of RF Signal	The RF signal is demodulated to extract the underlying information.
3	Analog-to-Digital Converter (ADC)	Converts the demodulated RF signal to a low-frequency baseband signal, transforming it into a digital format.
4	Protocol Detection Circuit	The digital baseband signal is processed to detect and navigate through specific communication protocols.
5	Decryption	The detected signal undergoes decryption for secure data processing.
6	Microcontroller Response Generation	The microcontroller processes the decrypted data and generates a corresponding response signal.
7	Encryption Circuit	The response signal is encrypted for secure transmission.
8	Digital-to-Analog Converter (DAC)	Converts the encrypted digital signal back into an analog format.
9	Modulation with RF Carrier Signal	The analog signal is modulated with an RF carrier signal.
10	Transmission via Tag Antenna	The modulated signal is transmitted back to the reader through the antenna, completing the communication cycle.

RFID Chip Frequency-Based Classification

Depending on the application, RFID chips utilize specific frequency ranges. Below we’ve summarized common frequency ranges and their appropriate data speed, applications, and collision systems.

RFID Chip Classification Based on Frequency

Frequency Band	Common Frequency	Data & Speed	Read Range	Usage Specialties	Applications	Antenna	Anti-Collision Protocol
Low Frequency (LF)	125 KHz	Low read speed, small amount of data (16 bits)	Short to Medium (up to 6 feet)	Works well with liquid and metal	Animal tracking, car immobilizer	Induction coil on ferrite core, or flat and many turns	Limited, difficult to read tags simultaneously
High Frequency (HF)	13.56 MHz	Medium read speed, small to medium amount of data	Short (up to 3 feet)	The most common type of RFID: NFC	Access control, ticketing, payment systems	Induction coil, flat, 3-9 turns	Potential capabilities, able to read tags simultaneously
Ultra High Frequency (UHF)	433 MHz for active; 860–960 MHz for passive	High read speed, small to medium amount of Data	Medium (up to 30 feet)	Has active tag, is the cheapest due to supply chain needs	Supply chain tracking, asset management, inventory solutions	Single or double dipole	Strong anti-collision capabilities, able to read tags simultaneously
Microwave Frequency	2.45 GHz or 5.4 GHz	High read speed, medium amount of data	High (up to 300 feet)	Has active tag, works well with liquid and metal	Container rail car tracking, automated toll roads	Single dipole	Prone to interference, able to read tags simultaneously

RFID Chip Memory

The memory block can be electrically erasable programmable RO memory (EEPROM), static random access memory (SRAM), or ferroelectric random access memory (FRAM). EEPROM, widely used due to its low manufacturing cost and ample reprogramming cycles, does have drawbacks, including high power consumption during writing operations and a limited write cycle.

In comparison, FRAM chips boast lower read power consumption and significantly reduced write times, but manufacturing challenges have hindered their widespread adoption. For the most popular NFC chips, the NDEF standard encoding format is used, adding compatibility and versatility to their usage.

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