GaAs FET IMD demands better standard

The third-order intercept point is an imaginary power level used to indicate the linearity performance of a 'well-behaved' power amplifier such as a bipolar transistor. Unfortunately, GaAs FET power amplifiers are by no means well-behaved devices. In fact, for most GaAs FET power amplifiers, the third-order intercept point is a meaningless term. However, more consistent ways of gauging linearity are available. A simple two-tone test, for example, could be developed into a standardized reference which could be applied uniformly throughout the industry. Digital radio presents an example of the manner in which this system could work. A graph is provided showing the performance of four GaAs FET linear amplifiers measured under large signal conditions.