Abstract:

Linear power amplifiers (PAs) are becoming widely used in modern wireless communication systems. The envelope of the signals in these systems is typically not constant, so that the PA design must address the issue of device nonlinearity in order to limit the amount of spectral regrowth, which can cause unacceptable levels of interference in the adjacent channels.

This research focuses on a new computational method for efficiently analyzing the relationship between spectral regrowth and physical distortion mechanisms in radio frequency power amplifiers. It utilizes a Volterra series model whose coefficients are computed from basic SPICE parameters. The analysis uses a decomposition of the Volterra kernels into simpler subsystems in order to greatly reduce the computation time.

The new computational approach was applied to the design of PAs using bipolar transistors as the active element. A series-based model was developed for representing the increase in active-device forward transit time at high collector current densities.

The design of a number of single-stage SiGe power amplifiers is also described. Bias techniques are described which allow the average PA current to increase at high signal levels and thus reduce distortion-inducing gain compression. The amplifiers were tested using the IEEE802.11b and IS-95 modulation schemes at different carrier frequencies and these results are compared with the theoretical analysis.