Impact of the Input Baseband Impedance on the Instantaneous Bandwidth of Wideband Power Amplifiers

This paper addresses the instantaneous bandwidth degradation of radiofrequency power amplifiers (RFPAs) still visible after eliminating all known causes related with the output matching network (OMN). First, the origin of this degradation, identified by the reduction of the PAs efficiency and linearity, is traced to the input baseband impedance terminations and a qualitative description of the phenomenon is presented. Then, an instantaneous bandwidth comparison is performed between two 30W GaN RFPAs, in which all impedance matching conditions are the same except for the input video-bandwidth impedance terminations. This work shows that, in addition to the adequate conception of the OMN, an optimally designed input impedance profile is also an important design consideration to retain the efficiency and linearity performance of RFPAs, for scenarios that require a wide instantaneous bandwidth.