Q-enhancement in RF CMOS Filters; Case Study: Direct Downconversion Transmitters for UMTS

This project concerns the use of Q-enhanced LC resonators in monolithic transmitters for UMTS. Among others, the UMTS conformance test specifies measurement of Adjacent Channel Leakage Ratio and Error Vector Magnitude. It is investigated how different circuit imperfections common for transmitters affect these parameters. Direct up-conversion is found to be the architecture that is most likely to generate efficient monolithic transmitters but they require a bandpass filter with a pass band in the low GHz range. Power losses in on-chip inductors make sharp bandpass filters based on passive resonators inefficient. Utilizing Q-enhancement it is possible to compensate for the losses the resonator with active circuits. One such circuit is implemented and an analytical expression describing the resulting Q-enhancement is derived. The Q-enhancement circuit is used in an on-chip LC resonator to demonstrate Q-enhancement. The circuit was more than capable of Q-enhancing the LC resonator.