Improved 60GHz loaded-line phase shifter using tunable inductor

Abstract

In this paper we propose a modified varactor loaded π-cell phase shifter to increase the phase shift range per cell and to minimize the input/output return losses over a large frequency band. A tunable transformer-based inductor is employed instead of the fixed inductor in conventional π-cell to keep the characteristic impedance of the line independent of the phase shift. In the proposed transformer based tunable inductor secondary terminals of the transformer are connected to a varactor to produce a variable inductor at the input of the transformer. To verify the operation principle, a 60GHz transformer in 65nm CMOS technology is EM simulated in HFSS and results have been imported into the circuit simulator for the overall characterization of the system with a varactor. A large phase shift of 480, average insertion loss of 3.5dB and input/output return loss of 10dB is achieved in the 60 GHz band.