Nonlinear Characterization of Multiple Carrier Power Amplifiers

In this paper the input signal dependence on the nonlinear transfer function of power amplifiers is discussed. It is shown by measurements that the nonlinear behavior of the amplifier does indeed depend on the input signal. This is seen to be true both for AM/AM and AM/PM distortion. The implication is that a traditionally VNA swept CW cannot be used to obtain the AM/AM and AM/PM distortion that will actually take place in the amplifier during real life conditions, and that test signals which closely resembles the signals that will actually be used are necessary. The focus is to present a new possible measurement methodology necessary to target the demands of accurate characterization raised by multiple carrier power amplifiers MCPA:s. We briefly discuss the mechanisms that lies behind this behavior. The test signal selection and creation is discussed, as well as a method of producing highly linear -80 dBc WCDMA signals for ACP testing. Finally we present practical measurement results on AM/AM and AM/PM distortion obtained with swept, pulsed and multi-tone input signals to prove the input signal dependence. Practical results is given for high power narrowband Class AB LDMOS amplifiers intended for the 2.11-2.17GHz WCDMA band and for medium power Class A GaAs FET amplifiers.