Image reject filtering in a direct sampling mixer

Abstract

Disclosed are methods, circuits and systems for image reject filtering in a multi-tap direct sampling mixer (MTDSM) of an IF or RF system. Disclosed is the use of rotating capacitors among the in-phase and quadrature branches of a signal processing system. The exchange of information among the branches of the I and Q channels is used in the implementation of a complex filter. Rotation of a switched capacitor CR between the I and Q channels of the circuit causes a sharing of the charge among the four paths, I+, I-, Q+, Q-, resulting in a direct sampling and a complex filtering arrangement (10). The preferred embodiment of the filter (10) shown can be seen to have four sub-circuits (12, 14, 16, 18), which may be understood as single-pole IIR filters. Embodiments using cascaded multiple stages of the complex filter to provide higher order complex filters are also disclosed.

Description

technical field [0001] The present invention relates to signal processing circuits and methods. More particularly, the present invention relates to methods and circuits for image rejection filtering in direct sampling mixers. Background technique [0002] Integrated radio transmitters and receivers have become increasingly popular. Efforts to provide intermediate frequency (IF) and radio frequency (RF) devices integrated on a single chip face many challenges. A particular problem is the need to eliminate or suppress image signals by providing bandpass filtering in transceiver devices designed for portable wireless applications. These applications require low power consumption, small silicon area, few external components and highly integrated single chip. [0003] Quadrature signaling schemes are known. Quadrature signaling incorporates the technique of processing the input in terms of an in-phase signal component (I) and a quadrature (Q) signal component using a carrier ...

AI Technical Summary

Problems solved by technology

This type of switched capacitor network suffers from the same power dissipation and cost issues as other switched capacitor networks, in large part because it relies on the use of operational amplifiers

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