Compact D-Band Passive Phase Shifters with Fine and Coarse Control Steps in BiCMOS-55nm

Programmable phase shifters are key building blocks in emerging Sub-THz phased array transceivers. This work proposes different structures to implement compact passive phase shifters in D-Band (110-170GHz). Tunable bandpass filters and variable-delay transmission lines are evaluated as phase shifters with fine control resolution over a limited range. To extend the range, 0°/180° and 0°/90° phase shifters are also investigated and implemented with a hybrid coupler and a switched $\lambda/4$ transmission line. Experimental results are presented on a test chip in a 9 metal BiCMOS technology with 55 nm MOS transistors used as switches. By combining the different structures, the full °/360° programmable range is covered from 120 GHz to 170GHz with a size of only $0.13\mathrm{m}\mathrm{m}^{2}$. The estimated insertion loss is aligned with previous works, but the remarkable footprint reduction facilitates the adoption in dense sub-THz phase array systems.