Overview

From APPLIED MICROWAVE & WIRELESS, VOL. 9, NO. 2, MARCH/APRIL 1997

The relationship between saturation, intermodulation distortion and spectral regrowth is important in the design and test of RF power amplifiers. A binary phase shift keyed (BPSK) signal using a 1010 data pattern is nearly identical to the two-tone signal used for intermodulation tests. This property allows evaluation (at a given bit rate) of both saturation and intermodulation from a single set of measurements on an amplifier. AM-AM and AM-PM characteristics measured using BPSK signals can be converted to polynomial models. Input modulation signals distorted by these models accurately predict the intermodulation distortion of the amplifier.

Introduction

The response of a nonlinear circuit to digitally modulated signals is sometimes difficult to predict from two-tone intermodulation tests [1, 2, 3] and/or network analyzer AM-AM and AM-PM measurements. This article demonstrates a connection between saturation measurements (AM-AM and AM-PM), the two-tone intermodulation test and digitally modulated signals. The twotone test stimulus is nearly identical to a BPSK signal using a 1010 data pattern, in which the tone spacing is equal to the modulation bit rate. By measuring the magnitude and phase of the modulation at the input and output of the amplifier, both the saturation and intermodulation may be found from a single set of data.

The linearity of an RF power amplifier at two different BPSK bit...