Improving FET Switch Linearity

RF field-effect transistors, especially pseudomorphic high-electron mobility transistors (pHEMTs), are commonly used as switches in communication applications. These small high-speed devices are vital for routing and conveying signals in such uses. The important characteristics of pHEMTs, besides their small size, are their high-frequency capability, insertion loss, isolation, power handling, switching speed, and linearity. A topology using a pair of simple but modified series and shunt elements was designed to improve upon the linearity of an RF switch. Each element of the switch was composed of a single, unbiased, but relatively long pHEMT, which was designed for the test. By shifting the position of the gate asymmetrically toward the source terminal in these transistors, it was found that the linearity was improved without cost to other performance parameters