Static electricity in a submicron world - ECE professor finds way to protect RF circuits without sacrificing performance

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By Doug Peterson, Freelance Writer
June 25, 2003

  • In radio-frequency (RF) integrated circuits, a persistent problem has been finding ways to protect components from static electricity without degrading the radio signal.
  • University of Illinois researchers have now found a way to help solve this dilemma. ECE Professor Elyse Rosenbaum explains that ESD protection devices act like overflow valves, channeling static electricity safely away.

dgpeters@dogwood.itcs.illinois.edu

 

Static electricity seems innocent enough, causing socks to cling to clothes or zapping people when they touch a door handle. But in the submicron world of electronics, static electricity packs a destructive punch. According to some estimates, electrostatic discharges (ESD) do more than $45 billion worth of damage to electronics worldwide each year.

ESD protection is built into integrated circuits to prevent static electricity from destroying sensitive microelectronic components. But in radio-frequency (RF) integrated circuits, a persistent problem has been finding ways to protect components from static electricity without degrading the radio signal.

University of Illinois researchers have now found a way to help solve this dilemma. ECE Professor Elyse Rosenbaum explains that ESD protection devices act like overflow valves, channeling static electricity safely away. But ESD protection can create headaches of its own in RF integrated circuits, which are embedded in wireless devices of all sorts, such as cell phones.

In a typical integrated circuit, the transmitted signal passes by the ESD protection without being disturbed. The ESD protection is invisible to the signal and doesn’t interfere with it, says Rosenbaum, who is a research professor at the Coordinated Science Lab on campus.

In an RF circuit, however, the signal is high frequency; and as Rosenbaum notes, ESD protection is not invisible to high-frequency signals. If the signal is equal to or greater than 1 gigahertz, it will see two pathways. As a result, some of the signal stays on the proper circuit path, but some of the signal is diverted toward the ESD protection.

In other words, some of the radio signal is lost.

“So the question with RF circuits is how to provide ESD protection without compromising performance,” Rosenbaum says.

Her answer is “resonant ESD protection circuits.” With this approach, the protection circuit’s resonant frequency, or natural frequency, can be designed to be the same as the RF carrier frequency. When this is done, the ESD protection is invisible to the radio signal. The signal isn’t diverted from its path, so it isn’t weakened. The bottom line: Performance is boosted.

Rosenbaum’s form of ESD protection, which was developed with funding from the Semiconductor Research Corporation, has been successfully demonstrated and is being tested by other researchers. It has applications in all types of wireless devices, she says, from cell phones to wireless Local Area Networks—all of which face the problem of preserving the signal while protecting against static electricity.

The study of static electricity dates back to 600 B.C., but the issue shows no signs of becoming ancient history. As electronic components continue to shrink, electrostatic discharge becomes an even greater threat. And this means that research such as Rosenbaum’s takes on even greater importance.

Editor's note: media inquiries should be directed to Brad Petersen, Director of Communications, at bradp@illinois.edu or (217) 244-6376.

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