DEPENDING ON THE APPICATION, an RF system's baseband processor or controller is a system-ona- chip (SoC) device that contains one or more central processing units (CPUs), memories, complex logic, and analog circuits. Normally, the digital baseband processor is implemented in advanced complementary-metal-oxide-semiconductor (CMOS) process technologies. The RF transceiver is generally manufactured using a silicongermanium (SiGe) BiCMOS process while the power amplifier (PA) is based on gallium arsenide (GaAs) or BiCMOS. Ideally, the RF transceiver and digital-baseband processor will be integrated into a single SoC. According to a five-page white paper titled, "Motivation for RF Integration" from Fujitsu Microelectronics America, RF CMOS is now an option for such integration.
Advanced RF CMOS processes have switching speeds that are fast enough for most of the wireless technologies either in use or in development. In addition, future CMOS process generations will make systems that operate between 30 and 300 GHz affordable. Thanks to transistor enhancements, engineers also can design high-gain, lownoise RF circuits with excellent dynamic range.
According to the white paper, passive components fabricated in advanced RF CMOS technologies are as good or better than those created with traditional RF processes. For example, RF CMOS commonly offers metal-insulator-metal (MIM) capacitors with unit capacitance from 1.0 to 2.0 fF/m2. MIM capacitors can be stacked to produce twice the unit capacitance in the same die area at the expense of additional process steps. RF-optimized process design kits (PDKs) also allow engineers to explore process variation spaces.
Fujitsu Microelectronics America, Inc., 1250 E.Aarques Ave., Sunnyvale, CA 94085-5401; (800) 866-8608, FAX: (408) 737-5999, Internet: www.fujitsu.com/us.