SiGe as an Enabler for Wireless Communications Systems *

Silicon (Si)–silicon-germanium (SiGe) heterostructures—and specifically Si–SiGe heterojunction bipolar transistors (HBTs)—are under extensive investigation, since they can provide nearly III–V levels of performance with the low cost of a Si-based technology. HBTs that utilize Si–SiGe heterolayers extended the high-frequency limit of Si-based bipolar technology to cutoff frequencies f_T, a frequency range that has been historically dominated by GaAs-based devices. In addition, fabrication processes for Si–SiGe devices are compatible with those routinely used for complementary metal oxide semiconductor (CMOS) integrated circuits (ICs), enabling the manufacture of Si–SiGe bipolar CMOS (BiCMOS) technology. When combined with the state-of-the-art digital CMOS devices, the SiGe BiCMOS technology offers a unique suite of devices to enable dramatic improvements in radio-frequency (RF)–analog–mixed-signal IC integration. This technology truly has become an "enabler" for single-chip implementation of highperformance wireless communications systems. This chapter shows the standard receiver architecture for wireless systems—the venerable heterodyne.