The use of RFID technology has grown considerably as the technology has found its way into many applications that were not on the initial target list. In addition to early applications such as product identification and security badges for access control, RFID technology now reaches into areas including anti-counterfeiting, shipping-container manifests/environment monitoring, mobile communications (cell phones), point-of-sale (POS) terminals, vending machines, smart advertising posters, and many other uses.
Standards for RFID subsystems are available from organizations such as the International Organization for Standardization. Standards specific to RFID can also be found on websites such as the RFID Network. One recent addition, The Electronic Product Code (EPC), is the next generation of product identification for RFID solutions. EPC is a simple, compact “license plate” that can uniquely identify objects (items, cases, pallets, locations, and more) for improved visibility. EPC is defined to express a wide variety of different, existing numbering systems like the GS1 System identification numbers, UID, VIN, and others.
EPC is a number designed to uniquely identify every single instance of an object. For example, every jar of coffee produced will have its own unique identity. Ideally, the EPC is the only information stored on a RFID tag including an EPC Manager Number (which could be a GS1 Company Prefix), an Object Class, and a Serial Number. It is important to understand that you must be an EPC global subscriber to register EPC Manager Numbers for use in encoding EPCs on RFID tags.
Of the many applications possible for RFID, anti-counterfeiting holds a great deal of promise to prevent the reputation of pricey brand-name products from being sullied. By embedding an RFID tag into the lining of a purse, a piece of clothing, in the label of an expensive bottle of wine, or on the wristband of a watch, vendors can ensure that consumers get what they pay for rather than a fake product that does not meet the brand’s quality standards. All the store selling the item has to do is scan the RFID code to collect the data and link back to the supplier’s website to provide proof of authenticity.
A brief RFID refresher
RFID technology allows data to be exchanged between two items, namely a reader/writer and a tag. Communication between the two items transfers information contained in the tag or the element carrying the tag to a system containing the reader (the host), and the host can then evaluate and take action based on the data.
An RFID system consists of several parts:
- An RFID reader/writer: The reader/writer communicates with the tags that come within the unit’s range. Typically, the RFID reader/writer will be in a fixed position and interrogates an RFID tag. In some applications, the reader/writer may also write data to the RFID tag.
- An RFID tag: RFID tags, also referred to as RFID transponders, are typically attached to or inserted into items that are mobile. The tags are small and generally very inexpensive so they can be used on items that range in cost from a dollar or two to thousands. Additionally, the tags are often considered disposable. Data contained in the tag is relayed to the reader, and in some systems it may also be possible to update the data within the tag to indicate that the item containing the tag has moved to the next stage in a process sequence.
- RFID application software: The host system will typically require software to read the data, process the data, and then save it or pass it on to another system. The software will often handle multiple reader/writers and coordinates and analyzes the data.
Additionally, RFID systems can operate on different radio frequencies as listed in Table 1. There are five different frequency bands: a low-frequency band spanning 125 to 134.2 kHz, two high-frequency bands (one at 13.56 MHz and the other at 433 MHz), and two UHF bands (one covering 860 to 960 MHZ, and the other at 2.45 GHz). Each of the bands has different characteristics that optimize that band for specific applications. The low-frequency band can transfer data at only 4 kbits/s, while the higher-frequency 13.56 MHz band can transfer data at up to 800 kbits/s. The amount of data provided by the tag can be as little as the equivalent of one bit (tag on/tag off) such as used by many retail stores to provide security if someone tries to walk out of the store with an activated tag. Active tags that contain a chip can typically contain a few dozen to tens of kilobytes.
Table 1: RFID standards as applied to frequency.
± 7 kHz
||Class 1 Gen 2
Tags are grouped into three basic types:
- Passive: Passive RFID tags are by far the most common. They do not contain any power and receive their operating power wirelessly from the RFID reader (Fig. 1). The amount of power is sufficient to power any component in the tag and reply with the required data. The so-called RFID smart tags (or RFID smart labels) are all passive. Furthermore, the tags use an antenna to capture energy from an RF signal emitted by the reader/writer.
- Semi-passive: This form of tag contains a battery to supply power for the internal operation of the tag, but relies on the RFID reader to supply the power to transmit the signal to the reader.
- Active: An active tag is one in which battery power is used to supply power to the electronic circuits in the tag. This extends the range of the tag and removes the dependency of the tag on received power to provide a reflected signal. This also allows the control and processing circuits in the tag to be more sophisticated, as in the case of the semi-passive RFID tag.
Figure 1: The basic passive RFID tag uses energy harvesting to collect power from an RF signal generated by the reader/writer circuit in the host system (Courtesy of Atmel).
The RFID tag and reader/writer communicate using a scheme referred to as the RFID coupling mechanism. There are several variations of the coupling scheme, including backscatter coupling or backscattering, capacitive coupling, and inductive coupling. The form of coupling that is used depends upon the intended application, and in turn the type of RFID coupling used will affect the choice of frequency for the system. The range of the RFID system can broadly be categorized into three groupings:
- Close range: within 1 cm
- Remote: between 1 cm and 1 m
- Long range: more than 1 m
Of these types of RFID coupling, magnetic and capacitive types are normally used for close-range links, inductive coupling for remote links, with RFID backscatter couplings used for long-range links. The antenna within the tag takes the largest amount of space. It must be able to operate satisfactorily at the frequency of operation. With wavelengths being smaller at higher frequencies (especially UHF and microwave), the antennas for these frequencies are more efficient versus the antennas for lower-frequency interfaces.
Implementing RFID solutions
To lower the cost of creating RFID tags and reader/writers, silicon vendors in cooperation with the various standards organizations and forums have developed ultra-low-power chips that can harvest the energy captured by an RF antenna to meet the cost/price points needed to make RFID solutions ubiquitous. Vendors such as ams
, DLP Design
, NXP Semiconductors
, and Texas Instruments
have all developed reader/writer and tag solutions that address various cost and performance points.
One unusual evaluation board for STMicro’s M24LR16E
, a dual-interface EEPROM tag, comes in the shape of a hand-sized robot (ROBOT-M24LR16E-A) and operates using a 13.56 MHz carrier (Figure 2a). The board contains the M24LR16 EEPROM, a 16-kbit electrically-erasable, nonvolatile memory that offers both a two-wire I²C bus and an antenna-port interface. The antenna is etched on the circuit board, and measures 20 x 40 mm. Also included on the board are an analog input for energy harvesting and a filter and switch on the voltage output pin of the memory chip, allowing the chip to either drive a LED indicator or supply an output voltage (Figure 2b).
Figure 2: Shaped like a robot, this hand-sized evaluation board for STMicro’s M24LR16 EEPROM tag contains the memory chip, an antenna, an LED indicator, and I²C memory interface (a). The memory tag is powered by a 1.8 to 5.5 V supply or by the received RF field and provides an energy-harvesting analog output that can drive an LED or provide a voltage to another subsystem (b).
The EEPROM’s memory is organized as 2 kwords x 8 bits in the I²C mode, and as 512 words x 32 bits in the ISO15693 and ISO 18000-3 mode1 RF mode. A unique 64-bit identifier is also included on the chip. The chip can operate from voltages as low as 1.8 V or be powered by the RF energy captured by the antenna.
A family of secure RF devices and cryptoRF products is available from Atmel. The AT88SC6416CRF-MR1
is a 64-kbit cryptoRF tag device that is mounted on an epoxy-glass substrate in the MY1 format. A companion reader chip, the AT88RF1354
meets the ISO14443 Type B specification.
Reader/writer module solutions developed by DLP Design include the DLP-RFID2
, also target operation at 13.56 MHz and are compatible with ISO 15693, 18000-3, 14443A/B, and FeliCa standards. The modules are available as surface-mount circuit board or USB stick and are powered by a 3 to 5 V supply. Either configuration includes an internal antenna and delivers a TTL-compatible serial data stream at up to 115 kbits/s. The modules also have the ability to both read and write data in addition to simultaneously reading the unique identifiers (UID) on up to 15 tags. To support developers, DLP also offers an RFID/NFC development kit, the DLP-RFID2-EDK
, which, in addition to the reader/writer module mounted on a circuit board, includes a MSP430
microcontroller from Texas Instruments and an LCD display module. A selection of various small-format antennas is also included. Source code for the development board was developed using the free version of the Code Composer Studio software from Texas Instruments.
Reader chips are also available from ams (austriamicrosystems). The AS3992
are UHF Gen 2 devices capable of handling EPC Class 1 and Class 2 in the 840 to 960 MHz UHF band (Figure 3). The chip provides designers with an integrated analog front-end, supplying all the protocol handling for EPC ISO 180006c/b 900 MHz RFID reader systems. Offering Dense-Reader-Mode filtering on the chip and improved sensitivity and pre-distortion compared to the company’s previous generation device, the AS3992 can be used in applications worldwide. Parallel or serial interfaces allow the reader to communicate with a host system.
Figure 3: The AS3992 RFID UHF reader circuit from ams contains a full analog front-end and EPC Gen 2 protocol-handling block, as well as both a serial and parallel interface to a host microcontroller.
For LF applications, ams offers the AS3933, a three-channel, low-power ASK receiver that can generate a wakeup upon detection of a data signal provided by a low-frequency carrier frequency between 15 and 150 kHz. An integrated correlator on the chip detects a programmable 16- or 32-bit Manchester wakeup pattern. The programmable features on the AS3933 allow the performance to be optimized to maximize distance while retaining a reliable wakeup generation. The chip’s sensitivity can also be adjusted to handle strong fields or noisy environments.
Also covering the 125 kHz and 13.56 MHz frequency bands, the Melexis MLX90109
, respectively, are full RFID transceivers. NXP also offers transponder chips for the same two-frequency bands: the HITAG HTS
family for the 125 kHz band and the SLRC400
, and CLRC632
for the contactless 13.56 MHz band. SkyeTek also offers several families of multiprotocol RFID radio modules. One example is the M1-Mini
, a complete reader/writer operating at 13.56 MHz that packs a Flash-based microcontroller that can be field upgraded to handle new features and new transponder protocols (Figure 4).
Figure 4: A complete reader/writer solution, the M1-Mini from SkyeTek packs an integrated antenna and a Flash-based microcontroller that can be field updated to provide new functionality and handle new transponder protocols.
Last, but certainly not least, several transponder options are also available from Texas Instruments. The TMS37157
works in the LF band at 134.2 kHz and consumes just 150 µA when active and only 60 nA in its power-down mode. Another HF band reader/writer from Texas Instruments, the TRF7964A
, includes user-configurable programming options, allowing the chip to handle a wide range of applications.
The breadth of applications leveraging RFID is continuing to increase, with areas such as drug monitoring/dispensing and other medical applications gaining momentum. Printer cartridges and laptop batteries are also starting to pack some form of RFID to prevent non-approved replacements from being used and potentially damaging the equipment or impacting the company’s reputation due to poor quality or early failures.
For more information on the parts discussed in this article, use the links provided to access product information pages on the Digi-Key website.
- The International Organization for Standardization (www.iso.org).
- The RFID Network (www.rfid.net)