A gain/phase imbalance minimization technique for LINC transmitter

A simple calibration scheme for correction of the path imbalance in a LINC transmitter has been demonstrated. In this algorithm a baseband DSP evaluates the gain and phase imbalance with a set of calibration signals through a feedback loop. Compensation of path imbalance is accomplished within the DSP by introducing a pre-distortion term. The quadrature errors of the I/Q modulators set a limit on the overall performance of this algorithm. A prototype LINC system has been tested for CDMA IS95 baseband input and -38 dBc ACI was achieved.