A Broadband GaN pHEMT Power Amplifier Using Non-Foster Matching

Abstract

Non-Foster matching is applied to design a multi- octave broadband GaN power amplifier (PA) in this paper. The bandwidth limitation from high-Q interstage matching is overcome through the use of negative capacitor, which is realized with a negative impedance converter (NIC) using the cross-coupled GaN FETs. For high power operation over the entire bandwidth, the natural interstage matching is optimized for the upper subfrequency band and the lower subfrequency band is compensated for by the negative capacitance presented by non-Foster circuit (NFC). Detailed analysis is presented to understand the frequency and power limits of NIC circuits for PA applications. Two negative impedance matched PAs (NMPAs) are fabricated with 0.25- $\mu$ m GaN pHEMT process. The implemented PA with $2{\times}$ combining shows the output powers of 35.7–37.5 dBm with the power added efficiencies of 13–21% from 6 to 18 GHz. The $4{\times}$ combining PA achieves over 5 W output power from 7 to 17 GHz. The NFC boosts the efficiencies and power below 12 GHz to achieve broadband performance without using any lossy matching or negative feedback. To our knowledge, this is the first demonstration of NIC-based broadband amplifiers with multi-watt-level output power.