Active Phase Shifter Using Symmetrical Polyphase Filter and Active Balun With Mitigated Imbalances for Ka-Band 5G Applications

초록

In this study, we design a CMOS-based active phase shifter operating at 26-30 GHz. In order to improve the performance of the phase shifter by suppressing the signal imbalance in the phase shifter, a polyphase filter (PPF) layout with a symmetrical structure is proposed. After that, the imbalance of the output signal due to the imbalance of the input signal of the symmetrical PPF is analyzed from the perspective of the magnitude, phase, and impedance of the input signal. Based on the analyzed results, a structure of an active input balun is proposed to suppress the magnitude and phase imbalance of the PPF input signal. An inductor is added to one of the differential output nodes of the proposed active input balun to suppress the output signal imbalance of the active input balun. The feasibility of the proposed symmetric PPF and active input balun is verified from simulation and measurement results. The proposed active phase shifter is fabricated through a 65-nm RFCMOS process. Under power gain conditions of -11, -10, -9, and -8 dB, the rms phase error and rms magnitude error are measured to be lower than 2.57 degrees and 0.44 dB, respectively. Here, the resolution of the phase variation is set to 5.625 degrees.

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