CMOS mixers and polyphase filters for large image rejection

摘要

This paper presents an in-depth treatment of mixers and polyphasenfilters, and how they are used in rejecting the image in transmittersnand receivers. A powerful phasor-based analysis is used to explain allncommon image-reject topologies and their limitations, and it is shownnhow this can replace complex trigonometric equations commonly found innthe literature. Practical problems in design and layout that limit thenperformance of image-reject upconversion and downconversion mixers arenidentified, and solutions are presented or limits explained. Thisnunderstanding is put to work in a low-IF CMOS wideband, low-IFndownconversion circuit, which repeatedly rejects the image by 60 dB overnthe wide band of 3.5 to 20 MHz without trimming or calibration