Power Amplifer Intermodulation Distortion Measurements

Power amplifiers have been used in communications systems for many years. The recent surge in demand for cellular phones, pagers, WLAN'S and other wireless communications devices has revived the interest in the design of these building blocks of the telecommunications industry. One of the important performance parameters for these power amplifiers is intermodulation distortion (IMD), which is a measure of the linearity of these modules. This linearity performance is critical where these power amplifiers are used in cellular base stations or wireless local loop transmitters since it relates to the density of the channel spacing, and therefore system capacity. A discussion of the IMD measurement techniques for power amplifiers and it's influence on the design methodologies is presented that starts with the basics of device characterization, optimized matching circuit synthesis and implementation for optimum IMD performance, parameter trade-offs and sensitivities, and multistage amplifier performance. A design example will then illustrate these concepts.