1–5 GHz 3.5-bit GaN MMIC Variable Attenuator With 55 dB Range

This letter presents a 3.5-bit variable attenuator (VA) MMIC that operates from 1–5 GHz. The MMIC is implemented in the Qorvo 250 nm BCB2 GaN-on-SiC process. An attenuation range of 55 dB in steps of 5 dB is achieved with resistive T networks and HEMT switch devices. The bit values are implemented with 5, 10, and 20/40 networks. The 20 and 40 dB resistive networks are combined into a single network, with the attenuation level determined by a switchable shunt resistance, resulting in an additional half bit. For the desired $10~\Omega $ and $1~\Omega $ shunt resistance values of the 20 and 40 dB T networks, the $R_{\mathrm { on}}$ of the shunt switch devices are used, balancing the $R_{\mathrm { on}}$ and $C_{\mathrm { off}}$ of the device. The VA demonstrates all 11 attenuation states with a return loss better than 10 dB across all states within a 5:1 frequency range and a minimum input P1dB of 34 dBm.