Design of single transistor stack direct-conversion mixers for low power and low voltage RF SoCs

Abstract

In this thesis, I propose two novel single-level down conversion mixers for direct-conversion receivers. The purpose of these researches is to develop low voltage and low power RF circuits for the current and near future system-on-chip (SoC) applications. The first one is SiGe sub-harmonic mixers for a 5.8 GHz wireless local area network service and the second one is CMOS down conversion mixers for an ultra-wideband wireless personal area network service. First of all, I propose a novel omitter/collector-coupled single-level sub-harmonic mixer. Although the sub-harmonic mixers have advantages over the conventional direct-conversion mixers in DC offset problem, LO self-mixing, and LO leakage, the use of lossy poly-phase filters complicates RF receiver structure due to the needs for LO amplifiers for compensating the poly-phase fitters`` loss. In this research, I insist a solution for the referred problems by using a novel circuit topology and a 90$\deg$ phase shifter. The SiGe sub-harmonic mixers consist of single level I/Q-channel mixers and 90$\deg$ phase shifters without using a LO buffer amplifier. The sub-harmonic mixers in this design generate I/Q base-band signals with single-ended RF and orthogonal LO input signals. The 90$\deg$ phase shifters generate orthogonal signals for each RF and LO input. A single-ended RF signal is orthogonally divided by an RC phase shifter, and the orthogonal output signals of the phase shifter enter the corresponding I/Q channel sub-harmonic mixers. Also, a single ended LO signal is orthogonally divided by an RC phase shifter and the both output of LO signals enter each sub-harmonic mixer. The down converter accepting single-ended RF and LO signal sources simplifies the whole RF block compared to conventional direct-conversion architectures which use fully differential components from LNA and VCO to mixer such as differential LNA and RF balun at RF signal path and differential or quadrature VCO and poly-phase shifter at LO ...