Qorvo

Many modern microwave electronic systems specify amplifiers with high output power, wide bandwidth, and high efficiency. Until recently, most wideband high-power amplifier (PA) solutions have relied on vacuum electronics-based technologies. Recent work, however, shows steady progress in realizing high-power, high-frequency, wideband amplifiers utilizing gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) technology that operates from near DC up to 7 GHz.
Qorvo designers were challenged to meet the requirements for an amplifier with high output power, wide bandwidth, and high efficiency by designing a 1-8 GHz PA MMIC fabricated with a 0.15 µm gallium nitride (GaN) process technology. The process featured a 100 µm thick silicon carbide (SiC) substrate and compact transistor layouts with individual source grounding vias (ISVs). The design utilized a non-uniform distributed power amplifier (NDPA) topology with a novel trifilar connected output transformer.
Design goals for the PA MMIC were: 1-8 GHz bandwidth, > 25 dB small signal gain, 10 W saturated output power, and power-added efficiency (PAE) exceeding 30 percent. A small-signal gain goal in excess of 25 dB required at least two amplification stages. To meet the bandwidth requirement, the NDPA topology was adopted and to increase output power, a novel monolithic trifilar coupled-line transformer design (patent pending) was used..
The Qorvo design team chose AWR Design Environment, specifically Microwave Office circuit design software, for this complex task. The two-stage amplifier demonstrated 9.3-13.1W of output power over a 1-8GHz bandwidth with greater than 29 percent associated PAE. Due to physical limitations regarding the location of the low impedance side tap, the microstrip implementation produced a ratio closer to 2:1. Electromagnetic (EM) simulations performed on the transformer using AXIEM 3D planar EM simulator within Microwave Office suggested that an 8:1 bandwidth could be supported with this approach.
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