Active Feedback Technique for RF Channel Selection in Front-End Receivers

Co-existence problems in a mobile terminal environment pose strict requirements on the linearity of a front-end receiver. In this paper, active feedback is explored as a means to relax such requirements by providing channel selectivity as early as possible in the receiver chain. The proposed receiver architecture addresses some of the most common problems of integrated RF filters, while maintaining their inherent tunability. Through a simplified and intuitive analysis, the operation of the receiver is examined and the design parameters affecting the filter characteristics, such as bandwidth and stopband rejection, are determined. A systematic procedure for analyzing the linearity of the receiver reveals the possibility of LNA distortion canceling, which decouples the trade-off between noise, linearity and harmonic radiation. A prototype designed in a standard 65 nm CMOS process occupies <;0.06 mm² and utilizes an RF channel-select filter with a 1 to 2.5 GHz tunable center frequency to achieve 48 dB of stopband rejection and a wideband IIP3 >; +12 dBm.