Blind Self-Calibration Technique for I/Q Imbalances and DC-Offsets

The gain/phase imbalances and DC-offsets in the in-phase and quadrature branches in direct conversion transmitters (DCTs) are main sources of errors, especially at microwave frequencies and above. These impairments distort the spectrum of the transmitted signal and degrade the communications performance. In this paper, a blind technique based on higher order statistics is proposed to estimate the calibration parameters in order to compensate for these impairments. By minimizing a cost function composed of second and fourth moments of the modulator output signal, the DC-offsets, gain imbalance, and phase imbalance can be successively calibrated. The convergence of the proposed technique is also analyzed. This technique is blind in the sense that it does not require any prior knowledge about the DCT input signal, and is applicable to many communications systems including QAM, OFDM, and SC-FDMA. Computer simulations and experiments at 20 GHz demonstrate that the proposed technique can significantly improve the DCT performance in terms of local oscillator leakage and image suppressions.