Design and Analysis of a 28 GHz Bandwidth DC Coupled Active Balun With Phase-Amplitude Compensation in 40-nm CMOS

This article presents the design methodology and the measurements of a DC-coupled wideband Active Balun fabricated in a 40-nm CMOS process. An auxiliary balun-based phase and amplitude imbalance compensation method is analyzed and implemented, providing broadband imbalance reduction. Differential T-coil peaking is utilized in each balun for bandwidth extension, and a resistive-feedback inverter is used to interface with $50~\Omega $ at the input. The designed Active Balun achieves 8.2 dB single-ended to differential gain with 28 GHz 3-dB bandwidth, with a peak phase and amplitude imbalance of 4 degrees and 0.3 dB within the bandwidth, respectively. The measured noise figure remains around 5 dB between 5-20 GHz.