A switched-capacitor image rejection filter, for complex IF receivers

This paper presents a switched-capacitor (SC) image rejection filter to solve the image problem in complex IF receivers, caused by mismatches between the in-phase (I) and quadrature (Q) paths. The proposed filter is actually a complex FIR Hilbert transformer with a notch frequency at + 1/4 f/sub s/, (f/sub s/ is the sampling frequency). An SC realization, as a part of the sampling units of the analog-to-digital convertor (ADC), is proposed. As demonstrated by circuit simulations, over 70 dB of image rejection can be achieved in the presence of 1% capacitance mismatch.