EFFECT OF SOURCE HARMONIC TUNING ON LINEARITY OF POWER GAAS-FET UNDERCLASS AB OPERATION

An effect of source harmonic tuning on linearity of power GaAs FET's u nder class AB operation is demonstrated. To improve efficiency of the power amplifiers, GaAs FET's are often operated under class AB conditi on. Due to lower bias current, a class AB amplifier begins to show non linearity at lower input power comparing with class A operation, and a s the power level of the input signal increases, however, an output po wer sometimes increases abruptly. From nonlinear circuit simulation, w e have found this phenomenon is occurred by the distortion in gate RF voltage, and by suppressing even-order harmonics in the input circuit of GaAs FET, class AB amplifiers can be effectively linearized. In thi s paper, we show the condition for improving the linearity of power Ga As FET's under class AB operation by the source harmonic tuning techni que.