A 100Watt ultra-broadband power amplifier using silicon LDMOSFETs

We present the design of a high-efficiency power amplifier using silicon LDMOSFETs for the ultra-broadband from 30 to 500MHz. The amplifier has a 4-way push-pull configuration using Guanella´s 1:1 transmission line transformer. To achieve both the high efficiency and the IMD3 required, the bias condition for the class-AB operation has been applied. In addition, a push-pull structure and a negative feedback network have been adopted for the broadband operation which has been implemented using broadband coaxial transmission line transformers and a broadband high-Q RF choke inductor. It is shown from the experimental results presented that the implemented power amplifier exhibits an output power at the 1dB compression point (P1dB) of more than 100W, as well as having a power-added efficiency of more than 35% at P1dB over the entire operational frequency band from 30 to 500MHz. The results also show very flat power gain characteristics of 40±1.5dB from 30MHz to 500MHz.