An Analytic Design Approach to Inverse Class-F RF Power Amplifiers


The design of high efficiency inverse class-F (class-F-1) radio frequency(RF) power amplifiers includes extensive measurements to characterizethe RF power device by means of the empirical load-pull test setup. Thispaper presents an alternative characterization approach based onevaluating the load impedances analytically at the desired harmonicfrequencies for a high electron mobility transistor (HEMT) in terms of theinternal and package elements of the active device. It additionally providesa method for extracting the parasitic elements of the power device as wellas determining the optimum load-line resistance using the transistormanufacturer’s large signal model. A new topology for the outputmatching circuit is also proposed with its synthetic procedure to presentthe appropriate harmonic load impedances. To verify this methodology, a900 MHz inverse class-F power amplifier circuit was designed and itsperformance was tested with the aid of the Keysight ADS software. Thesimulation results showed an output power of 38 dBm, a power gain ofabout 13 dB, DC-to-RF efficiency greater than 87%, and an acceptablelevel of linearity for both GSM and CDMA modulated signals.