Up until the mid-1990s the wireless communication market was dominated by designs in the III-V semiconductor processes, such as Gallium Arsenide (GaAs) or silicon bipolar technologies. Before that time, complementary metal-oxide semiconductor (CMOS) processes could not achieve the high transit frequencies (fT) required at transmitter/transceiver front ends. But CMOS was and continues to be the clear choice for implementing digital circuits, as it is the lowest cost, high-volume semiconductor fabrication technology available.
Driven by the prospects of lower cost designs through increased integration of analog and digital content on the same chip and the replacement of expensive GaAs front end circuitry with less expensive CMOS implementations, the development of RF CMOS received a great deal of attention.
For example, FIG. 1 illustrates a diagram of conventional transit frequencies for CMOS and Silicon Germanium (SiGe) processes at different technology nodes. Notably, the 90 nm CMOS node with a transit frequency fT greater than about 140 GHz enables systems operating around 60 GHz to be designed completely in CMOS.
Recently, there has been a growing interest in exploiting the frequency band surrounding 60 GHz for short-range high-data-rate wireless communications. This particular frequency band is gaining popularity because of its high attenuation (10-15 dB/km), which is caused by atmospheric oxygen for a band approximately 8 GHz wide around 60 GHz. Although high attenuation prohibits long distance communication, it enables frequency re-use over short distances. These piconets have radii on the order of a few meters and are standardized by the IEEE 802.15 working group for wireless personal area networks (WPAN).
For instance, in the United States, the Federal Communications Commission (FCC) assigned the 59-64 GHz frequency band for general unlicensed usage. In Japan, the band from 59-66 GHz is regulated for high-speed data communication. In Europe, the 62-63 GHz and 65-66 GHz bands have been provisionally allocated for mobile broadband systems and the 59-62 GHz band is allocated for Wireless Local Area Networks (WLANs).
Referring now to FIG. 2, it illustrates that storage capability of hard drives and other data storage devices is increasing exponentially, and will soon move to the order of terabytes. As this trend continues there is a need for devices facilitating fast data transfer between these devices. The recent spectral allocation around 60 GHz for high-data-rate communications coupled with the recent advances in CMOS processes enabling designs at these frequencies point to fully CMOS systems being a low-cost and commercially viable solution to this challenge.