RFID Technology Is Revolutionizing Businesses: A Look at How TVS Semiconductor Devices Protect RFID Circuits

 

Tracking merchandise to prevent losses is a popular use for RFID technology. By fitting goods, vehicles, even pets with RFID tags, their whereabouts are easier to pinpoint. Other applications include access control, toll roads, event attendee tracking, bus/railway ticketing, medical patient monitoring, airport baggage sorting and routing, IT asset and inventory management, food chain tracking, and future Internet of Things (IoT) applications.

As small as RFID components can be (the smallest RFID chip currently is 0.05 mm × 0.05 mm), they require a complex combination of advanced electronics to function effectively.

MDE Semiconductor, Inc. provides a range of transient voltage suppressors to help protect RFID circuits from transient overvoltages for any myriad of applications. Specifically, we offer the MAX-40 Series of TVS Diodes, which are TVS semiconductor devices that can divert high energy transients (as high as 40000 W) safely to ground while offering low capacitance and excellent clamping ability.

Adequate protection enhances the customer’s experience where products will be exposed to harsh environments that can negatively impact performance. Some applications such as security and healthcare are critical, so that anything other than long-term reliability is unacceptable. This article describes the characteristics of RFID systems and the circumstances related to their usage that makes overvoltage protection necessary.

 

What is RFID?

RFID, short for radio frequency identification, is a means of communicating over short distances – wirelessly, and cheaply. Using radio waves to transfer data, computers can capture information about an object (in fact, several objects at a time) automatically without contact and without needing to be within the line of sight of the object(s).

 

Components of RFID Systems

In general, an RFID system consists of two important parts:

  1. RFID Reader: Includes an RF transceiver (transmitter and receiver), an antenna system, a signal processor, a controller unit, and a data interface to a host system. The transmitter continuously sends out radio frequency signals and depending on the system, can range between a few centimeters to 20 meters or more. The receiver identifies and the processor decodes the information stored in an RFID tag in the range of the reader’s signal.
  2. RFID Tag: Includes a low power integrated circuit, an antenna system, data modulator, and logic control. The microchip has an electrically erasable and programmable read-only memory (EEPROM) which stores the useful data (e.g., unique identification code) that will be read and transmitted.

 

Categorization of RFID Systems

RFID systems are difficult to categorize into neat boxes because of the wide variety of component types and wave frequencies used for their construction and operation. These characteristics influence their level of performance and the practical application of a system. Below are a few important differences.

Wave Frequencies

The industry has worked towards some standardization for radio frequencies. However, different countries worldwide still have their preferred spectrum bands for RFID systems. The most common ones are:

  • Low frequency (125-134kHz): Ideal for animal tagging and access control where short reading ranges of 1-10 cm are sufficient.
  • High frequency (13.56Mhz): Suitable for reading ranges between 10 cm to 1 m and applications such as passport security and library books.
  • Very high frequency (865-960MHz): Useful for long reading ranges of about 6 m, and for reading multiple items at once. This application is ideal for tracking warehouse assets or determining race car positions at the finish line.

Active vs. Passive RFID Tags

Active tags have a battery supplying the power required to function. Furthermore, they are constantly sending out signals with their encoded information. Whenever real-time data is needed over a long read range, active tags are preferred such as, in logistics for tracking land and ocean containers, and military assets. They are built to survive harsh environments and for their batteries to last as long as 5 years. This combination of features makes them expensive.

Passive tags are more widely used because they are reliable and are cheaper too. They don’t have batteries but are activated using energy from the electromagnetic field created by a reader (through induction). They are excellent for file tracking, smart labels, supply chain management, and more.

 

Protecting RFID Systems From Transient Voltage Events

In general, a transient voltage event is a high energy impulse induced into an electrical circuit from external sources. It is characterized by a short duration and could be repetitive or random. Examples of external sources include electronic discharges (ESD) and lightning strikes.

As we saw already, RFID tags and readers contain complex electronic circuitry in extremely small packaging which makes them susceptible to these kinds of electric stresses. The antennas of readers and tags together with their microprocessors operate at very low voltages. These components have conductive paths to other systems and are unable to handle the high currents associated with transient events. Without protection, a voltage spike will likely lead to the failure/destruction of the devices.

Also, the environment in which RFID devices will be used can increase the risk of transient overvoltages to significant levels. For example, consider an implanted chip in a human body that is exposed to the high voltage discharge from a defibrillator due to an emergency, or a reader operating in the highly energetic field of a lightning event. Adequate protection ensures that the devices continue to operate normally after the event.

There are recognized techniques for achieving electrical transient protection including blocking, isolation, and suppression. Fuses and circuit breakers are effective for blocking but need to be replaced or reset after they have been activated. Isolation devices include bulky and expensive transformers, although they don’t require replacement after activation. Suppression involves the use of TVS semiconductor devices like metal oxide varistors and TVS diodes, which are inexpensive in comparison and perfect for cost and space-constrained RFID applications.

 

How TVS semiconductor Devices Protect RFID Circuits From Transient Voltage Events

A TVS semiconductor device connected in parallel to a sensitive RFID chip provides an alternative pathway for transient energy, protecting the chip in the process.

TVS diodes, in particular, are sought after because they respond faster (picoseconds) to electrical transients compared to other types of TVS semiconductor devices like MOVs or gas discharge tubes.

TVS diodes are designed with p-n junctions that have larger cross-sectional areas compared to normal diode junctions to conduct electrical transient currents to ground without sustaining damage. Under normal operating conditions, a TVS diode offers a high impedance to the RFID circuit. However, when the voltage exceeds safe levels, the TVS diode operates in avalanche mode, whereby cascading electrons collide with each other to free up more electrons and provide a path to ground for the transient current.

The specification details of the sensitive RFID components will determine the characteristics of the TVS diode capable of providing adequate transient protection. Important parameters include:

  • Reverse working voltage – At this voltage the diode acts like a high impedance capacitor. It conducts no electricity in this state.
  • Reverse breakdown voltage – At this voltage, the TVS diode changes to low impedance and begins to conduct electric current due to the avalanche effect.
  • Peak pulse current – Above this maximum current specified for a TVS diode, the protection device will be damaged.
  • Maximum clamping voltage This is the maximum voltage drop across the TVS diode equivalent to the peak pulse current. The TVS diode should be selected such that its clamping voltage (when the diode “comes on”) does not damage the RFID system under protection.

Since signal integrity is critical for effective RFID operation, a TVS diode with low capacitance should be selected (large capacitance diminishes signal integrity). Also, a diode with low reverse leakage current will maximize the efficiency of the system.

 

The MAX-40 Series of TVS Diodes by MDE Semiconductor, Inc.

The MAX-40 series are high-performance, low capacitance TVS diodes that offer an excellent combination of features to protect RFID systems from high-energy transient events.

They are manufactured using the company’s distinctive low leakage glass passivation process that achieves high-energy absorption capabilities. The MAX-40 series offer low peak clamping voltage to prevent circuit shorts during a transient event. The diodes are housed in miniaturized (weight 1.490 ± 0.149g) and fully encapsulated packages with minimal footprint for unobtrusive circuit design. What’s more, the series is offered in different surface mount and through-hole board mounting options. To prolong the battery life of the application, diodes in the series, e.g., MAX40-12CA, are characterized by low reverse leakage current of <1nA.

With new applications of RFID systems continuously being devised, protecting their internal circuits ensures reliability and high-performance. MDE Semiconductor, Inc. offers technical support and design assistance for any challenge in your design. Datasheets (for our TVS semiconductor devices) and contact information are available on our website http://www.mdesemiconductor.com