L. Schwoerer and C.P. Gupta (Germany)
Quadrature Error, Filter Mismatch, I/Q Mismatch, Direct COnversion Receiver
Typical Direct Conversion Receivers suffer mainly from Quadrature Error, i.e. non-ideal phase-shift of 90+ d between I- and Q-mixer, and mismatch of the analog filters in the I- and Q-branch. A mathematical model is presented, that gives an interpretation of the Quadrature Error as projection of the received complex signal onto a sheered coordinate system. Filter Mismatch is modeled by multiplicative Delta-Transfer-Functions both in I and Q. This paper gives some constraints for the filter mismatches, such that their impact on the system performance is negligible. With these constraints, two simple Quadrature Error Correction schemes are derived, that can compensate Quadrature Errors of up to 20 with minimal hardware effort.
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