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

Abstract

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 stop-band 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 65nm CMOS process occupies < 0.06mm 2 and utilizes an RF channel-select filter with a 1-to-2.5GHz tunable center frequency to achieve 48dB of stop-band rejection and a wideband IIP3 > +12dBm.

An integrated CMOS passive transmitter leakage suppression technique for FDD Radios

“…Most of the work has been reported so far using active methods to do the leakage cancellation including feed-forward filtering [8][9], active two port cancellation [10], LMS adaptive filter [15] and feedback filter [16][17]. All these techniques try to tap the PA output and inject an amplitude adjusted and phase rotated signal into the RX path to cancel the leakage signal.…”

“…1-8(a) and Fig.1-8 (b). Fig.1-8 (a) proposes a feedback loop incorporating the receiver's down-conversion path [16] while Fig.1-8 (b) has a separate rejection loop after the LNA, which needs an additional down-converter [17].…”

Frequency translation loops for RF filtering : theory and design

“…Consequently, the analysis accurately predicts main performance parameters of the system such as stop-band rejection, in-band loss and loop stability, and can thus be used for both system design and optimization. In contrast, the idealized analysis [50], although much simpler and can serve as a preliminary design guide, is shown to be quite inadequate in predicting such performance parameters.…”

“…This paper provides a detailed circuit analysis of frequency translation loops employing passive mixers by solving the frequency domain equations of the system in an iterative manner to obtain an accurate closed form solution. The analysis developed here is based on the negative feedback receiver architecture presented in [50], i.e. it assumes a frequency translation loop that incor-porates the IF part of the receiver chain.…”

“…By substituting (3.4) -(3.6) into (3.2), it can be shown that the RF channel filter bandwidth is [50] …”