Design and optimization of CMOS switches for switched tuning of LC resonators

Switched tuning of RF integrated circuits has had a reputation of being inferior compared to continuous varactor tuning due to excessive loss in the switches. This paper models CMOS switches and switched capacitance tuning of LC resonators. Closed form expressions are derived that show what the optimal switch size is and what the corresponding Q-value is. Finally a comparison is made between different layout styles. These results show that switched tuning is a very attractive alternative to varactor tuning.