Microwave Engineering Europe - April 2008 - (Page 33)

CMOS PAs 33 semiconductor process is required to provide a highgain, high-frequency transistor element with a highbreakdown voltage. The hybrid packaging technology provides high-Q passive components to generate the 50-ohm matching circuit. Implementing in standard CMOS means the designer has to live without enhanced transistors and high-Q passives, making the development of a fully integrated PA extremely challenging. Recently, a new technique has emerged that makes it possible to design a PA using CMOS processes, such that it can be housed in a simple plastic package. Distributed active transformer (DAT) technology, as it is called, employs a geometry that enables a relatively lowQ semiconductor metal to be used to provide a transformer-based matching circuit, eliminating the need for a module package. Distributing the PA core into several blocks and combining the power using the transformer structure means, in conjunction with several other patented techniques, that a high-breakdown transistor is not required. Originators of the DAT technique built on research by the California Institute of Technology in Pasadena, Calif. Further innovation at Axiom Microdevices, the commercial producer of DAT-based PAs, perfected the productization of a General Packet Radio Service (GPRS) PA device, solving application-speciﬁc problems, such as receive band noise and operation from a high-voltage battery pack. Unlike GaAs equivalents, with the power core now on CMOS, the small-signal control circuitry required to bias and regulate the power of a GPRS-type PA may now be integrated in the same die as the main power stages, further reducing costs. Integration of the PA core also provides more ﬂexibility in supporting linear modulation schemes. Traditionally, designers have used one of two methods – the ‘brute force’ method, which employs a linear modulator and PA, or the more elegant “envelope reconstruction” method, in which a nonlinear, highly efﬁcient PA becomes the core of a polar modulator. In the case of the latter, using a traditional PA construction technique poses signiﬁcant challenges. For example, a PA core implemented in a specialty process will have a different response to variations in temperature and process than its linearization circuitry. This usually leads to the extremely undesirable requirement that the end user, or handset manufacturer, must increase his factory calibration times to compensate, thus increasing costs. Conversely, having the PA core on the same die as its controller provides access to multiple points either for monitoring or control actuation. This gives the designer more options when developing a transmission architecture with best-in-class performance and cost structure. The next logical step is to further integrate the PA with other cell phone components, such as the baseband and transceiver modules, which, as previously mentioned, are already being implemented using the CMOS process. The DAT-based CMOS PA technology has recently proved to be viable for use within a standalone GPRS product through the large-volume production shipments of Axiom’s AX502 device. It also has the potential for future integration, which will help the industry continue to address and fulﬁll the demands of manufacturers and designers for chip sets that are smaller and more cost-effective, and that offer broader feature sets. David Kang (kang@axiommicro.com) is vice president of engineering at Axiom Microdevices Inc. RF & Microwave Solutions Fast. Flexible. For you. Whether it’s custom filters or stock components, you need solutions tailored for your unique requirements. And you need them fast. At Trilithic, innovation is about more than engineering and technology. It’s about listening to your needs and expectations. So together we can create solutions that work for you – today and tomorrow. To find out more, call (800) 344-2412 or visit www.trilithic.com. Microwave Engineering ● April 2008 ● www.mwee.com 030-031-032-033_MWEE.indd 33 27/03/08 15:58:06 http://www.trilithic.com http://www.trilithic.com http://www.mwee.com

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Microwave Engineering Europe - April 2008 News Contents Comment Test and Measurement: Comprehensive WiMAX and Wi-Fi Product Design Demands Effective Channel Emulation Military/Aerospace Focus: Hardware Needs Limit Software Radio Interview — Mitsubishi Electric Europe: GaAs Technologies Spanning High-End Space and Radar Through to Cost-Sensitive Handset and LNB Applications How Do You Test ZigBee Transmitters? Advanced Receiver Design Boosts Performance CMOS PAs Pave the Way for One-Chip Phones Products Calendar

Microwave Engineering Europe - April 2008

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