Highly-Integrated, Low-Noise, Dual-Output GaN DC/DC for GaN Solid State Power Amplifier Supplies in Space Applications

In this work a highly-integrated, 24 V input, dual-output (5 to 1SV up to 1A and −1.3V up to 100mA), low-noise GaN-based DC/DC supply for the gate and drain bias of a GaN solid state power amplifier for E- and W-band applications in space ór phased-array applications is presented. By using two fast-switching GaN half-bridges as the main element of two highly-integrated DC/DC converters for gate and drain bias supply, $\approx$50% higher efficiency and an adjustable drain voltage (e.g. for orbital tracking) can be achieved compared to state-of-the-art solutions (LDOs only). The required drain supply of the GaN SSPA (5 to 18 V with currents up to 1 A) is generated by a 70 m$\Omega$, 100V monolithic GaN half-bridge based buck-converter switching at 3.1 MHz with high gate-resistors $(62\Omega/10\Omega)$, extended filtering (resulting in an ac voltage noise of below 5 mV RMS for most bias points) and efficiencies above 80% for the whole output current range. The gate supply $(-1.3\mathrm{V},\ \leq 100\mathrm{m}\mathrm{A})$ is provided by a multi-stage approach to achieve efficient conversion and low noise: In the first stage the battery voltage is down converted to 5 V in a 3.1 MHz buck-converter $(\eta\geq 90\ \%)$ with two 3.3 $\Omega, 65\mathrm{V GaN}$ transistors, to optimize the efficiency of the second stage. The second stage (switched capacitor, 2 MHz circuit, $\eta\geq$ 80%) converts the voltage to −2 V. A final LDO stage converts the −5V to −1.3 V with $0.8 \mu \mathrm{V}$ RMS-noise, to avoid instabilities of the SSPA due to gate bias oscillations. The converter is not actively cooled and does not exceed a local hotspot temperature of 85 °C at any operation point.