Efficient Method to Measure IMD of Power Amplifier with Simplified Phase Determination Procedure to Clarify Memory Effect Origins

Takeshi TAKANO
Yasuyuki OHISHI
Shigekazu KIMURA
Michiharu NAKAMURA
Yoshimasa DAIDO
Kiyomichi ARAKI

IEICE TRANSACTIONS on Electronics   Vol.E93-C    No.7    pp.991-999
Publication Date: 2010/07/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E93.C.991
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Recent Progress in Microwave and Millimeter-Wave Technologies)
power amplifier,  IMD measurement,  memory effect,  bias impedance,  even order nonlinearity,  

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This paper describes a time-domain expression based on the physical model of power amplifiers where electric memory effect is considered to be caused by even-order nonlinearity and bias impedance. It is demonstrated that the time-domain expression is consistent with the general memory polynomial reported by D.R. Morgan et al. To confirm validity of the physical model, a simple method is proposed to measure amplitude and phase of IMD by two tone test: the phase is extracted from measured small signal S-parameters of the amplifier under test. The method is applied to a GaN FET amplifier under condition that memory effect is enhanced by applying inductive cable for DC supply. Frequency dependent IMD is fitted by a parallel connection of L, C, and R: it has been confirmed that the frequency dependence of IMD is given by the bias impedance at even order harmonics of envelope frequency. The frequency dependence assures the validity of the physical model as well as the time-domain expression.