Interference Rejection at a Radio Receiver Input Exploiting Selective Feedback

The aim of this thesis is to study the feasibility of using feedback immediately at the antenna to improve the out-of-band linearity of receivers. The idea is to reject all signals at the antenna node, except for those in the wanted band, i.e. to effectively create a high-Q RF filter at the input of the receiver. An exception should be made for the desired signal which is available as a zero-IF baseband signal which is likely possible by upconverting it, breaking the feedback loop for the wanted signal. During the course time of the report, two architectures and a seperate chapter for performance improvement techniques in terms of linearity are introduced. The main difference between the proposed architectures is the location of the gain stage. The first architecture has a feedback gain. Due to noise problem, the gain is moved to the forward path and the second architecture is formed. The resulting noise figure was found to be similar as in the case of a simple single stage common-base LNA. The linearity of the block itself also does not show a difference, but the interferers at the adjacent channels were attenuated at the input of the filter which brings more flexibility to the linearity constraints of the following building blocks of the receiver.