A 6-bit Phase Shifter at E-band Using a Feedback-Controlled Variable Attenuator

A 6-bit phase shifter operating at E-band (71 GHz to 76 GHz) is presented. The differential phase shifter is based on a vector modulator topology, using an accurate variable attenuator to achieve variable gain in the I and Q branches. The accuracy is achieved using combination of a feedback control circuit and a replica circuit. Implemented in a 55 nm BiCMOS technology, the phase shifter measures $\pmb{930} \mu \mathbf{m}\times \mathbf{410}\ \mu \mathbf{m} (\mathbf{1965} \mu \mathbf{m}\times \mathbf{1080}\ \mu \mathbf{m}$ including test baluns and pads). The circuit achieves an RMS phase error of 2.1° and an RMS amplitude error of 0.36 dB over the band of interest.