Abstract
In this letter, a 6-bit ultra-wideband phase shifter for active phased arrays is presented in 0.18 mu m SiGe BiCMOS process. A differential two-stage transformer-based poly-phase quadrature signal generator with over 100% bandwidth is proposed and analyzed. The vector modulator consists of a common-base buffer for polarity selection and invariant input impedance and variable gain amplifiers (VGAs) with an active inductive load for bandwidth extension. The 360 degrees full-span vector-modulator phase shifter achieves a 5.625 degrees resolution and 0.9 dB peak gain with 0.99-3.75 degrees and 0.82-0.94 dB RMS phase/gain error at 5 to 18 GHz. The core area of the circuit is 0.98 mm x 1.55 mm.