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RF modules pose tough test challenges.

Article Excerpt
By Rick Nelson, Editor-in-Chief

Engineers at EPCOS employ multiport vector network analyzers to test multifunction miniature front-end modules that support multiple wireless communications standards.

MUNICH, GERMANY--The proliferation of wireless communications devices is creating a voracious demand for the RF components and modules that make those devices work. The components must, of course, be small enough to fit comfortably within the mobile wireless consumer products they populate and not crowd out ancillary functions like MP3 players and digital cameras. And because consumer products increasingly support multiple communications standards, the miniature devices themselves must incorporate the functionality necessary to implement WiFi, WiMAX, Bluetooth, GPS, DVB-H, UWB, and the various multiband cellular technologies.

On the digital side, Moore's Law has enabled vendors to make great strides in providing increased functionality within a single CMOS integrated circuit. Radios, however, require numerous other active and passive components as well as baseband digital chips, power amplifiers, switches, and low-noise amplifiers. Discrete passive components don't follow Moore's Law and are not amenable to continual miniaturization. Christian Block, VP and CTO of the SAW division at EPCOS (see "The Evolution of EPCOS, p. 36) described the problem--and the solution--in a 2004 interview (Ref. 1). "Major progress can no longer be made by continuing to miniaturize discrete passive components alone," he said. "So we are opting for passive integration based on LTCC technology."

LTCC drives miniaturization

"LTCC" refers to low-temperature co-fired ceramic technology, which EPCOS uses to create multilayer ceramic substrates that embed passive components. Compared with the FR4 material or laminates, LTCC substrates provide lower loss and allow for the integration of many passive components in a compact space (Ref. 2).

An LTCC module, said Dr. Patric Heide, director of product development for modules at EPCOS, might have anywhere from 10 to 20 layers, with each layer between 30 and 50 microns thick. Within those layers, EPCOS can build inductors and capacitors to implement filter functions and baluns. Dr. Heide explained that to help the drive toward miniaturization, the modules also accommodate semiconductor chips such as power amplifiers and switches typically fabricated in GaAs technology. "We've developed a lot of...

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