Overview

From APPLIED MICROWAVE & WIRELESS, VOL. 9, NO. 4, JULY/AUGUST 1997

The gain compression (AM-AM distortion), phase distortion (AM-PM distortion) and spectral regrowth of an RF amplifier can be found in the measurements of the complex modulation envelope. The relationship between distortion and spectral regrowth is explored by modeling the AM-AM and AM-PM distortion, and then simulating spectral regrowth from the distortion model. Comparison of the measurement and model results shows that when hysteresis is present in the amplifier AM-AM and AM-PM distortion, a model with memory is needed to predict the spectral regrowth accurately (within 1 dB).

Spectral regrowth and adjacent channel power (ACP) are common specifications for transmit amplifier linearity in wireless digital communication systems. For design and test purposes, it is useful to have a way to analyze how amplifier characteristics, such as AM-AM and AM-PM distortion contribute to spectral regrowth [1, 2, 3, 4]. Sampling the modulation envelope at the input and output of the amplifier [5, 6] enables the AM-AM, AM-PM and spectral regrowth to be measured simultaneously from a single set of data.

This article compares the spectral regrowth calculated from models with and without memory to the experimental measurements of an amplifier using BPSK signals. The model results are compared to the experiment in two cases: where the amplifier saturation has no hysteresis (1 kbps bit rate) and where the amplifier saturation exhibits significant hysteresis (100 kbps bit rate). A polynomial (memoryless) model...