X-Parameter Characterization of LDMOS Devices for Broadband Doherty High-Power Amplifier Design

We present a novel design approach of high-power broadband Doherty amplifier (DPA) by the X-parameters. It is based on the nonlinear vector network analysis of the 3-port circuit composed of the main and peak power devices, connected to the input network. The technique permits the analysis of the best termination for both the peak and main devices, mutually interacting by the input network, and development of the broadband output networks which optimizes the mutual devices load modulation. The three-port nonlinear vector characterization method was applied to the analysis of a broadband DPA designs based on a pair of Silicon Laterally Diffused MOSFETs (LDMOS) with optimized peak power and efficiency in the 700 MHz to 960 MHz bandwidth. The DPA performance exhibited a peak power of 54.2 dBm at center frequency with a peak drain efficiency up to 71.5%. and a drain efficiency in excess of 68%.