Buck DC-AC converter using gallium-nitride FETs for amplitude-modulated class-E RF power amplifiers

This paper presents the analysis and design of the pulse-width modulated (PWM) buck dc-ac converter used as a dynamic power supply for amplitude-modulated class-E radio-frequency (RF) power amplifier (PA). The buck dc-ac converter operates at a fixed input voltage and a variable output voltage. The differences in the inductor current profiles of the buck dc-ac converter and the classical buck dc-dc converter are highlighted. The design equations required to estimate the minimum value of the inductance of the buck dc-ac converter in continuous-conduction mode and consequently, the minimum value of capacitance are derived. A suitable design example is presented for the buck dc-ac converter operating at a fixed input voltage VI = 14 V, a variable output voltage 2 V ≤ VDD ≤ 12 V, switching frequency fs = 100 kHz and supplying power to a class-E RFPA with a maximum output power PO = 10 W and a carrier frequency fc = 1 MHz. Simulations are performed for the buck dc-ac converter and class-E RFPA comprising of gallium-nitride (GaN) field-effect transistors. In this paper, the anti-parallel diode of the GaN transistor is used as the freewheeling diode in the buck converter. Finally, few concluding remarks discussing the effectiveness of the buck converter as an amplitude-modulator is presented.