Online calibration of quadrature low-IF receivers

In theory the quadrature low-IF receiver topology eliminates image filters required by the heterodyne topology. In practice analog component mismatch between the I/Q signal paths allows image energy to leak into the desired signal, limiting performance. Existing compensation techniques fall into three categories: offline, signal specific, and blind. In this paper a scheme is proposed that continually injects a calibration signal into the image band at the input of the receiver. This scheme allows the mismatched low-IF receiver system to be calibrated without taking it offline, without signal specific knowledge, and without the performance limits of blind techniques