| Voltage controlled oscillators (VCOs) are key components in frequency synthesizers for Radio Frequency (RF) wireless communications. The design of monolithic VCOs with standard CMOS processes has been the object of several recent research projects. The common goal of these attempts has been to investigate the possibility of meeting the very demanding VCO phase noise specifications without making use of bipolar processes or external components. Two categories of VCOs are studied in this thesis, one involving an inductor, and the other is inductor free, which is a ring oscillator.; The study of the phase noise performance of complementary LC VCO shows that most of the phase noises come from the tail current. A modification has been made based on this topology, where the tail transistor is removed. However this brings another problem: higher power consumption. To overcome this problem, sub-threshold techniques have been used leading to sub-threshold LC VCO. A Ring oscillator is designed at the end because of its wide tuning range and ease of implementation. Schematic simulations, layout and post-layout simulations are accomplished using TSMC 0.18 um CMOS technology. The performances of the three types of VCOs are compared regarding the oscillating frequency, phase noise and tuning range. All of these can be used in the Bluetooth applications. In addition, the figure of merit (FOM) of the designed VCOs is compared with work by other researchers. |
