RFID tags come in many types and categories, and choosing the right type is important for the best application. This article aims to gain insight into the choices made when designing RFID tags and how these aspects affect the application.

An RFID tag consists of three distinct components: the RFID chip, which consists of an integrated circuit (IC), an antenna, and an underlying layer/substrate (called a substrate). These components are usually not created in-house by the label manufacturer, but rather spread the workload to other manufacturers.

With passive RFID, when the tags are not interacting with the reader, they have no power at all. Once the reader initiates the data exchange, it first drives the antenna, typically 15 to 50 microseconds, to charge and power the tag's capacitors.

The data exchange is done through a method called backscatter modulation. When the tag turns the load on and off, the voltage on the reader's antenna changes. The process is like a transformer: the reader is connected to the primary winding and the tag is connected to the secondary winding. Reducing the secondary load affects the primary winding.

Finally, RFID tags can be custom for the intended use. These customizations are mostly found in accessories, allowing the user to choose the one that best suits the environment and connection method the tag will encounter. Other customizations include size, power options, and frequency.

Passive RFID tags are divided into two main parts: the analog front end and the digital part. Front-end tasks include all analog processing of the DC power supply, input signal detection and information extraction (called demodulation), and transmission of the modulated signal. The digital section decodes incoming data, reads and writes internal EEPROM (electrically erasable programmable read-only memory) memory in response to commands from the reader, and encodes and transmits the data to the modulator. 

A backscatter modulator is a device used to modulate the impedance seen by the transponder antenna when transmitting (a measure of the resistance of a circuit to current flow when a voltage is applied), which determines the overall performance of the tag.

The analog front end is the key module of passive RFID transponders. It provides regulated power to the digital core and other circuits by correcting the incoming RF signal. In transmit mode, the analog front end also works to ensure that its backscatter modulated communication method works properly.

Passive RFID devices derive their operating energy from radio frequency waves emitted by an RFID reader. The wireless link is divided into two categories according to the wireless link coupling mechanism: near-field coupling and far-field coupling. Near-field coupling is essentially an inductive coupling with frequencies up to a few MHz, forcing the reader close together, so the coupling coil of a near-field coupled RFID will have a large voltage at its terminals and will not be severely affected by nearby devices. This is not the case for far-field coupling.

In the case of near-field passive wireless systems, a diode bridge rectifier can be used to convert the carrier signal to DC.

On the other hand, far-field RFID tags require an efficient method of converting RF to DC. Due to the low voltage of the antenna, a voltage multiplier is used which increases the voltage level when performing the conversion.

Antennas are a critical part of designing readers because they need to efficiently transmit signals to and from tags. PCB traces are often used to form loops. The scope of a label is affected by a number of factors, such as:

The antenna size of the tag. Larger antennas are easier to detect.

The reader's antenna size. Larger antennas increase read range, but noisy environments may result in worse signal-to-noise ratios and reduced read distances

Antenna direction

Ambient noise

The Q factor of the antenna. Typically, a Q between 30 and 40 is required.

Most designs target antennas between 0.8 and 1.6µH, as values below 0.8µH, become increasingly difficult to synchronize. Maximum energy transfer occurs when the antenna and associated components are in resonance.

In order for the tag and reader to communicate, the impedance presented to the transponder antenna must be changed to modulate the reflected power. To achieve this change, a transistor is inserted between the two antenna terminals, which when turned on shorts the antenna terminals, effectively presenting a short, cutting off the flow of power and signal. When the transistor is off, it has no effect on the antenna and the rest of the modules. The process of changing the impedance is a modulation based on backscattering.

Modulation is the process of modifying the properties of a signal (called the carrier) to convey information. These properties include amplitude, phase, and frequency. For example, Amplitude Shift Keying (ASK), as its name implies, modifies the amplitude of a signal. The protocol standard selects the amplitude modulation used to transmit data from the reader to the tag. From then on, the signal needs to be demodulated to extract the information.

The above describes the design principles of RFID tags in detail. If you want to know more or want to customize RFID tags, please contact us.

Yanzeo is a professional custom RFID reader and tag manufacturer. We have always been guided by intelligent technology for many years, and have been committed to the research and exploration of barcode and RFID technology. With hundreds of independent technology patents, it is a well-known barcode and RFID equipment manufacturer. One of the business and solution providers.