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ESD Protection for Wi-Fi® Antennas and Other RF Applications

Figure 1 ESD entry into an antenna system
Figure 1 ESD entry into an antenna system

As smartphones, tablets, point-of-sale (POS) terminals, and other mobile devices become ever more prevalent, they are becoming increasingly exposed to electrostatic discharge (ESD) from a charged human body or object, making them more vulnerable to permanent damage or deterioration. There are two types of ESD strikes: 1) contact discharge caused by contact with an exposed connector and 2) air discharge that produces an electric spark, invading an antenna or internal loop wiring. It is necessary to protect mobile devices from these ESD events. Nowadays, it has become the norm to test the ESD tolerance of exposed leads and add ESD protection as necessary.

 Therefore, these circuits are sometimes not protected against ESD. An antenna is connected to radio-frequency (RF) ICs and other sensitive devices. Although the RF IC shown in Figure 1 incorporates ESD protection circuits, they typically provide an ESD tolerance of less than 1 kV HBM (human body model). Although this ESD protection level is sufficient in manufacturing and other ESD-controlled environments, it does not suffice for environments in which mobile devices are generally used. Proper ESD protection must be considered not only for the ESD protection diode alone, but also for the entire system, including the ESD protection circuitry incorporated in the RF IC.
This application note provides an answer to one of the frequently asked questions about the considerations required for the selection of ESD protection diodes.

ESD enters an electronic system from an antenna and might damage or degrade an RF circuit. In particular, RF front-end ICs such as global positioning system (GPS) receivers are fabricated using a nanoscale process in order to satisfy system requirements. ICs with smaller geometries are less tolerant of ESD.
Receive-only antenna systems for GPS and FM radios generally handle micro-power signals whereas Wi-Fi® and other transceiver antennas transmit high-power signals in transmit mode. However, the requirements for ESD tolerance and high-power signal transmission are contradictory. The following sections describe the considerations for the ESD protection of RF transceiver antenna lines from three perspectives:
 

  1. The quality of an RF signal should not be degraded when there is no ESD event
  2. The device under protection (DUP) should not be degraded or destroyed in the event of an ESD strike
  3. Considerations for board design

* Wi-Fi is a registered trademark of Wi-Fi Alliance.

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