M.Sc Thesis

M.Sc StudentWeiss Roy
SubjectLow Loss Integrated N-Path-Filter-Based Circulator
DepartmentDepartment of Electrical and Computer Engineering
Supervisor ASSOCIATE PROF. Emmanuel Cohen
Full Thesis textFull thesis text - English Version


Full-duplex is a system architecture where the transmitter and the receiver operate at the same time and at the same frequency. Using a passive shared-antenna interface in a high-end Full-Duplex system dictates the use of a circulator. Conventional circulators rely on magnetic materials and cannot be integrated on silicon. However, previous work have shown that an N-Path-Filter-Based circulator can be integrated in a standard CMOS process, which suits perfectly for mass production applications such as mobile communication.

In the first part of this work, the integrated N-Path-Filter-Based circulator is thoroughly analyzed. Simplified linear time invariant (LTI) circuit models are introduced in order to perform the analysis. These models are then verified by comparison to the complex linear periodic time varying (LPTV) model of the circulator. Exploiting the insight acquired from the simplified models, a new and improved topology for the integrated circulator is proposed. The simulated sum of Tx-to-Ant insertion losses (IL) and noise figure (NF) are less than 1dB at 100MHz and less than 2dB at 2GHz. These results are ~2dB better than the previously reported state-of-the-art integrated circulator. This significant expected improvement lead to second part of the work.

In the second part, the design considerations, trade-offs and implementation of the local oscillator (LO) generator are discussed. Specifically, the impact and importance of LO phase noises (PN) and rise/fall time. The concept of baseband negative resistance and its advantages are introduced. Finally, the layout of the non-reciprocal phase shifter (NRPS) test chip and the predicted performance of a circulator based on this NRPS are presented. The simulated NF and Tx-to-Ant IL of the designed circulator are ~1.4dB @2GHz and the Tx-to-Rx isolation is better than 22dB @2GHz.

At the time of writing this work, the NRPS test chip and a test board were being manufactured. Once the manufacturing is completed, the performance of the NRPS chip and the circulator would be evaluated in the lab and reported accordingly.