Design and analysis of CMOS baluns for 94 GHz image radar and 28 GHz 5G communication system

Abstract

Two W-band CMOS elliptical baluns (i.e. balun-1 and balun-2) for 94 GHz image radar, and one miniature Ka-band CMOS square balun (i.e. balun-3) with short-terminal and input capacitor (for elimination of the inductive imaginary part of the input impedance at the input port) for 28 GHz 5G communication system are demonstrated. These baluns are applicable to a down-conversion mixer for conversion of the single RF and LO input signals to differential signals. They are also applicable to a phase shifter for conversion of the single I and Q signals (from the quadrature coupler) to differential I (i.e. I + and I −) and Q (i.e. Q + and Q −) signals. Instead of the traditional balun structure that uses three sections of thin M5 (or M8) interconnection lines (underneath the thick top M6 (or top M9) main structure), the proposed balun structures use only one section of thin M5 (or M8) interconnection line to enhance S21 and S31. Balun-2 (with M9 main structure thickness of 3.4 μm) attains S21 of − 4.98 to − 4.57 dB, S31 of − 4.85 to − 4.59 dB, amplitude imbalance magnitude (AIM) smaller than 0.15 dB and phase difference deviation (PDD) smaller than 4° for 90–100 GHz. Balun-3 (with M6 main structure thickness of 2.34 μm) occupies a small chip area of 0.042 mm2, and achieves S21 of − 4.97 to − 4.44 dB, S31 of − 4.68 to − 4.29 dB, AIM smaller than 0.28 dB and PDD smaller than 2.3° for 27–29 GHz. The prominent results of these baluns indicate that they are suitable for W-band and Ka-band systems.