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The new interest in high frequency applications such as 5G and mmWaves have increased the design requirement for the integrated circuits, specifically for the signal generation and base-band processing stages. The Rotary Traveling Wave Oscillator (RTWO) has been proposed not only as clock distribution network when is used in arrays (ROAs), but also for high data rate applications and communication systems. The RTWO has two ring-shaped differential transmission lines as resonator and this resonator ring cannot be built with a constant characteristic impedance due to the characteristics of the CMOS manufacturing processes. The most complex discontinuity of the RTWO resonator is the Mobius connection; this discontinuity is generally manufactured using angles of 90° or 45°, different metal levels and stacks of intermetallic connections (vias). In this work we analyze and model the 45° Mobius connection for different geometrical configurations and technologies. The results show that the Mobius connection commonly implemented using the last two top metal levels is not the optimal and by using a lower metal layer is possible to select the optimal cross-connection in this type of oscillators.

In this work, a simple electric circuit model for the evaluation of the impact of vias (inter-metallic vertical connections) in resonant rotary traveling wave oscillator (RTWO) is proposed. A test structure was designed to quantify the degradation on the signal integrity of RTWOs caused by these vias. The test structure and the RTWO were designed according to the rules of the 130 nm commercial mixed mode, Single-Poly 8-Metal (1P8M), P-substrate, RFCMOS technology. The vias test structure consist of vertical inter-metallic connections and respective metallic pads. According to the used technology, the test structure was implemented using copper for all the metals layers. Simulations were performed using advanced tools: a 3D electromagnetic simulator (EMpro) for the extraction of the electrical properties of the test structure, HSPICE for electrical simulation and Mentor Graphics IC Studio for the geometric pattern (layout) design of the test structure. Finally, a 26.87 GHz RTWO was designed to quantify the performance of the oscillator under the effect of the vias.

In this paper, the effects of geometrical discontinuities and topological structure on Rotary Travelling Wave Oscillators (RTWO) are studied. Using the 3D electromagnetic simulator EMPro Simulation Software Design Platform, we have found that reducing the corner discontinuities can increase the oscillation frequency up to 3.34%. Additionally, we observed that the topological structure of the RTWO affects also the different performance parameters, since as more folds and overlaps between metallic levels present the structure, the oscillation frequency is reduced and the power consumption of the RTWO resonator is increased.