Bounded performance technique for broadband amplifier design

Abstract

In this paper we propose a new technique to use load-pull data for broadband power amplifier design as an alternative to the simplified real frequency technique (SRFT). Like SRFT the bounded performance (BP) technique optimizes a matching network over many discrete frequencies that span the operating bandwidth. Unlike SRFT, BP optimizes the match over a Smith chart area defined by design specifications and load-pull data. From this area, we deduce a simple cost function for optimizing the matching network. The technique alleviates the problem with broadband point matching, where a physically realizable matching network cannot trace the trajectory of the optimal reflection coefficients of a power transistor over a wide frequency range. It also includes design specifications into the formulation of the optimization cost function, thus ensuring the design will meet the required performance. Using a 15-W Qorvo GaN HEMT plastic device and BP technique, we designed and built a C-band 4–5 GHz amplifier. We measured on average 18-W output power and 56% drain efficiency from 5 first-pass amplifiers. Results from testing 1 amplifier with 20-MHz LTE signal and without pre-distortion showed maximum adjacent channel power ratio of −38.5 dBc and maximum alternate power channel ratio of −49 dBc at up to 32.5 dBm average output power, or 9 dB back-off from saturation.