Experimental Demonstration and CAD Investigation of Class B HFET Transistor Operation at Microwave Frequencies

A vector corrected large signal measurement system has been configured to enable all four large signal voltage traveling waves at the transistor terminals to be measured even when the transistor output is terminated with an arbitrary load impedance. With this system the user can observe and control in real time ("waveform engineer") the output current and voltage waveforms by varying the load impedance ("load-pull in the time domain"). The ability to operate HFETs in the high efficient Class B mode at 2.5 GHz has been experimentally investigated using this measurement system. In addition, this configuration also allows look-up table model generation and validation to be performed with the same system, improving significantly the model accuracy. Simulated performance using such look-up table model was in very close agreement with that measured, thus allowing the model to be used to study and interpret the measured Class B operation at microwave frequencies.