Introduction to Wireless Circuit Design
Wireless circuits are not that different from commonly known two-way radio, television, and broadcast arrangements. Some of them require high linearity in modulation (TV picture); some work via relay stations (two-way radio). The real differences lie in the fact that the cell sizes are much smaller, and that in most cases we attempt multiple channel use (reuse) using time-division multiplex, spread spectrum, or some other efficient means of reducing the bandwidth required for communication. One can argue that the wireless circuits include simple devices, such as garage-door openers and wireless keys for automobiles (we have seen many cases where strong interfering signals prevented the car owners from reclaiming their cars until the interfering signal disappeared). Another longtime favorite is cordless telephones: initially, 50-MHz models with essentially no privacy protection; later, more sophisticated models that operate at 900 MHz; and now, dual-band designs that use 900 MHz and 2.4 GHz.
The largest wireless growth area is probably the cellular telephones. The two major applications are the handsets, common referred to as cell phones or occasionally as “handies,” and the base stations. The base stations have many more problems with large-signal-handling linearity at high power, although handset users may run into similar problems. An example of this is the waiting area of an airport, where many travelers are ...