Low-Noise, 24 V, 1 A, 2.1 MHz GaN DC/DC Converter for Variable Power Supply of a GaN-Based Solid-State Power Amplifier

This work presents the design and analysis of a low-noise, 24 V input and variable output voltage, 2.1 MHz DC/DC converter based on a 100 V, $70\ \mathrm{m}\Omega$ Gallium Nitride (GaN) monolithic half-bridge with maximum 1 A converter output current up to 15 V. The converter can be used as variable and highly efficient DC power supply of GaN solid state power amplifiers (SSPA) in E-band as opposed to the conventional low dropout regulators, improving the overall SSPA power efficiency. The converter (0.036 in3) achieves an overall efficiency of above 80 % over nearly the whole output voltage range and a peak efficiency of $> 91\%$, depending on the gate resistor, at a power density of above 300 W/in3. The achieved voltage peak amplitude varies from below 20 mV to above 200 mV, again strongly depending on the value of the gate resistor. The AC voltage ripple is below 2 mV for all converter designs, making it suitable for low-noise supply of the power amplifiers drain terminals and to replace the conventional inefficient low-dropout voltage regulators. A comprehensive analysis of the tradeoff between switching speed, efficiency and high-/low frequency voltage noise is carried out to highlight the potential of GaN based low-noise DC/DC supplies. Finally, measurements are performed with different DC supplies (LDO, switch-mode power supply unit, and the GaN DC/DC converter from this work) with an E-band transmission chain to demonstrate the usability of this approach. It can be seen that the GaN DC/DC converter supplies the SSPA with no difference to the state-of-the-art solutions and does not cause any oscillations/instabilities, but can increase the efficiency of the power amplifier by 40 %.