Effect of gate‐to‐source capacitance of high‐power Si‐LDMOS FET on the asymmetrical intermodulation and modulation bandwidth of base‐station amplifiers

Abstract

This letter presents the effect of the gate‐to‐source capacitance (Cgs) on the imbalance of the intermodulation distortion (IMD) and modulation bandwidth of Si‐LDMOS field effect transistor (FET) high‐power base‐station PAs. It is revealed that the strong Cgs nonlinearity at the input gate of the LDMOS significantly contributes to the output intermodulation imbalance and plays an important role in determining the modulation bandwidth. The Volterra series analysis is used to qualitatively understand and describe the mechanism. The frequency‐sensitive baseband impedance, which is presented to Cgs and is proven to be one of the main factors to the imbalance in the analysis, is experimentally changed by manipulating the bias circuitry. The output IMD imbalance behavior is examined with two‐tone signals for the PA with the MRF5S18060 Si‐LDMOS FET. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2448–2451, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24597