A front-to-back-end modeling of I/Q mismatch effects in a complex-IF receiver for image-rejection enhancement

Insufficient image-rejection due to I/Q mismatch limits complex-IF receivers´ application in modem wireless communication systems. This paper proposes a new modeling method to effectively enhance such kind of receiver image-rejection performance, through an understanding of the correlation between the different image-reject functional blocks. The presented complex-IF receiver mainly consists of a Double Quadrature Down-Converter (DQDC) and an Analog-Double Quadrature Sampling (A-DQS) scheme for the frequency down-conversions. Systematic analysis of the I/Q mismatch issues will be presented first. Then, according to the analyzed results and assuming that the total required image-rejection is 70dBc, an optimum combination of allowable mismatch in the functional blocks is obtained as an example for DCS1800 application. Such combination is verified through non-ideal behavioral simulations and is further discussed in terms of its practicability in CMOS implementation.