A K-band 5-bit digital linear phase rotator with folded transformer based ultra-compact quadrature generation

This paper presents a K-band 5-bit vector modulator phase rotator. A fully differential based on a 6-port folded transformer I/Q generation passive network generates the quadrature signals at K-band with low loss, wide bandwidth and high precision, all within an ultracompact foot-print; this makes the phase rotator design especially suitable for large-scaled high-density phased array systems. Two linear digital VGAs scale the quadrature signals to achieve the desired vector phase interpolation. As a proof-of-concept design, we implement the phase rotator in a SiGe BiCMOS process within a compact chip area of only 310 μm by 380 μm. It achieves -3 dB bandwidth of 6 GHz at the center frequency of 23.5 GHz. The maximum RMS phase error is only 2° for phase interpolation over the full 360° phase span. It consumes 4 mA from 2.5 V and the measured P_1dB and IIP₃ are -16 dBm and -5.5 dBm, respectively. Leveraging the dense phase interpolation points to calibrate undesired I/Q mismatch is also demonstrated, which shows the robustness of the design.