Fewer external components translate into lower manufacturing costs for the end user and generally higher reliability for the resulting circuit.
Semiconductor suppliers have been active during the last few years, trying to keep pace with existing and emerging standards and trends in wireless electronics. In the history of the microwave industry, there has never been a time when specifiers have had more choices in semiconductor processes and types, from traditional silicon to high-speed/low-noise silicon germanium (SiGe) and even new gallium-based materials such as gallium nitride (GaN). Can so many choices possibly be bad?
Of course, with so much diversity comes the task of sorting through the possible options and understanding the differences in technologies. Many semiconductor suppliers offer chip sets (with transceivers, transmit amplifiers, and baseband controllers) for wireless-local-area-network (WLAN) applications at 2.4 and 5 GHz. In general, the small-signal and digital chips are based on silicon processes (such as CMOS), while the amplifiers are usually built on GaAs (for its superior electron mobility and high efficiency). Since these devices are designed to conform to various WLAN standards, such as IEEE 802.11a, b, and g, they provide similar RF performance levels, although their DC characteristics, including power consumption and bias requirements, may vary widely. When investigating active devices for a given standard, be it Bluetooth, a variant of PCS/CDMA, GSM, or WLAN, specifiers must delve deep into a data sheet for a meaningful comparison. Of course, one fairly simple way to compare different semiconductors is by their required bill of materials (BOM) for a given application—how many additional circuit elements, such as RF chokes and bypass capacitors, are needed along with the chip set. Although not always true, usually simpler is better; fewer external components translate into lower manufacturing costs for the end user and generally higher reliability for the resulting circuit.
Apologies to any RF semiconductor suppliers omitted from our survey (p. 33), and special thanks to Editorial Assistant, Dawn Prior, for her research efforts in assembling the list of RF/microwave semiconductor companies. Although many names will be familiar to RF engineers, keep an eye on some of the newer firms, such as Centellax (www.centellax.com, Santa Rosa, CA) and Nitronix Corp. (www.nitronix.com, Raleigh, NC) for future developments in two very promising technologies: SiGe and GaN, respectively.