A CMOS Sub-Harmonic Passive Mixer Having Low Flicker Noise with Back-gate Coupling LC-Tank Quadrature VCO

Abstract

A sub-harmonic passive mixer and LC-tank QVCO (Quadrature Voltage Controlled Oscillator) are presented in this thesis. Both of them are designed to be useful for multi-band wireless communications (WCDMA, WiBro and CDMA2000 1x). The designed mixer is a passive component. Thus, the mixer doesn't have any gain. Despite of that, the reason why the mixer has been chosen is that it is possible to reduce a f licker noise which appears in the desired band. Moreover, the mixer provides better linearity than an active mixer. In order to enhance the isolation between each port, the mixer uses a sub-harmonic frequency. As a result of that, a problem like DC offset because of the self-mixing phenomenon is significantly reduced and the QVCO could be alleviated. The designed QVCO operating on WCDMA, WiBro and CDMA2000 1x is a differential structure, which NMOS and PMOS transistor are used, to have low power consumption. The oscillation frequencies of the QVCO are half of standards. Since the current source can increase in phase noise, it is excluded from this structure. For flexible band selection of the QVCO, it has MOS switches for multi-band selection, but they also affect phase noise, so the size of transistor should be selected carefully. Moreover, MOS varactors are employed for channel selection. The frequency tuning range of the designed VCO is from 800 MHz to 1.2 GHz. A fully integrated multi-band Mixer cascaded with a VCO is designed with TSMC 0.18-μm RF CMOS process.