Comparison of CMOS VCO Topologies

In this work the phase noise behavior of integrated LC VCOs in 130 nm SiGe BiCMOS technology is investigated. Three different VCO topologies i) Full NMOS ii) Full PMOS and iii) Complementary NMOS PMOS structures have been considered for investigation. Through circuit level simulations, the dependency of the phase noise on various parameters like frequency of operation, transistor type, transistor width and transit frequency has been studied and various tradeoffs will be discussed and validated. Using foundry based RF transistor models the comparison of the VCOs has been made at three different operating frequencies: 5 GHz, 15 GHz, and 25 GHz. It will be shown that with ideal passive elements, the PMOS VCO structure achieves the best phase noise performance at 15 GHz and higher operating frequencies.