Design and Analysis of Ka-Band Variable-Gain Phase Shifter With Impedance-Invariant Vector Modulation

This article presents a 32–38-GHz variable-gain phase shifter (VGPS) with a novel impedance-invariant vector modulation technique for highly precise phase and amplitude control. A negative-feedback magnetic-coupling (NFMC) method is proposed to stabilizes input and output impedances of variable gain amplifier (VGA), and it effectively alleviates the impedance variations at the different currents biased from the current digital to analog converter (DAC). The VGPS is fabricated with a 0.13-μm SiGe BiCMOS technology. It achieves a 7-bit phase resolution over 360^∘ and a 4-bit gain adjustment across a 7.5 dB dynamic range. The VGPS demonstrates exceptionally low rms phase and amplitude errors of 0.33^∘/0.10^∘ dB in phase shifter mode and 0.23^∘/0.08^∘ dB in VGA mode at 35.5 GHz. The chip occupies a core area of 1062 × 534 μm² and consumes only 7.4–12.2 mW dc power.