Comparative Layout Study of Stacked CMOS Synthetic Quasi-TEM Lines Separated by the Meshed Ground Shield and its Application to 180 $^{\circ}$ Hybrid Design

This work investigates the coupling phenomena of the synthetic quasi-TEM transmission lines (TLs) with the differential layout in multilayer structure. The numerical method based on the normal mode parameters calculates the couplings between two stacking TLs shared with a common mesh ground plane. The theoretical investigations show that the TL in the orthogonal layout has the lowest coupling. This result is applied to design a 60 GHz 180 ° hybrid using the standard 0.18 μm 1P6M CMOS process. The prototype is realized by the TLs with an orthogonal stacked layout in a size of 180 μm × 240 μm without the contact pads. Both measurements and the simulations show the return loss lower than 15 dB and the isolation higher than 20 dB at the frequency between 55 and 65 GHz. Two insertion losses (|S₃₁ | and |S₂₁|) are 4.9 ±0.2 dB and 5.4 ±0.3 dB, respectively. From 56 to 64 GHz, the phase difference between two output ports is about 180° ±10°.