A 77-GHz Power Amplifier in a 90-nm GaN Process

This paper demonstrates a three-stage 77-GHz MMIC PA in a 90-nm GaN process under development. Only a single device-size non-linear model was available and no device scaling allowed. Resulting in a limited staging ratio of 1:1:2, four $\mathbf{8} \times \mathbf{5 0} \mu \mathrm{m}$ HEMTs are used for two drive stages and an output reactively power-combined stage. Small-signal measurements show 7.1 dB of gain, which is about a 4 dB degradation compared to simulations. Due to the drop in gain and limited available power, the peak PAE and power could not be reached in measurement. Two PAs are cascaded by wire-bonds to compensate for limited available drive power. Measured large-signal performance for the cascaded amplifiers at $P_{{in }}=9 \mathbf{d B m}$ shows $P_{{out }}=22.5 \mathbf{d B m}$, a large-signal gain of 12.78 dB and $P A E=2.5 \%$. The chip layout with 6 individual PAs allows for additional off-chip power combining.