Millimeter-wave Rat-race Balun in a CMOS 65nm Technology with Slow-wave Transmission Lines and Innovative Topology

An integrated rat-race coupler for balun applications based on high quality factor Slow-wave CoPlanar Waveguides transmission lines (S-CPW Tlines) at millimeter wave frequen- cies was realized in the 65-nm CMOS technology from STMicroelectronics. Optimized criteria for a CPW phase-inverter and Tlines' characteristic impedance enable to minimize insertion loss and surface on the die. The various building blocs were designed thanks to 3D full wave EM software coupled to a circuit simulator. Thanks to the S-CPW Tlines, the device occupies a small area of 0.085mm 2 . From 51GHz till a minimum of 67GHz, i.e., a 16GHz bandwidth, the measurements show the return loss is lower than i15dB. The magnitude imbalance of the measured couplings are included between to i4:2 and i4:1dB and i6:5 and i6dB, respectively, and are really ∞at over a wide bandwidth. Finally, in the bandwidth the phase shift between the output ports is kept very ∞at, equal to 175:9 - § 0:4 - , while the isolation is better than i26dB. The rings are smaller than 290"m on a side. It shows the potential of this approach for further increasing working frequencies.