A Novel Gain, Phase and Offset Calibration Scheme for Wideband Direct-Conversion Transmitters

Conventional direct conversion architecture for an RF transmitter is characterized by a single up-conversion stage using high frequency quadrature modulator. The architecture is however very sensitive to quadrature gain imbalance, phase skew and dc offsets in signal path. In this paper, a simple yet highly effective novel automatic calibration scheme is presented to achieve remarkably high image and carrier rejection ratios for a board level RF transmitter system. The proposed technique can correct gain imbalance, phase skew and offset impairments of in-phase (I) and quadrature (Q) channels in an IQ modulator. The calibration is implemented in software and therefore, can be performed in the field. Measurements demonstrate that proposed scheme can achieve more than 80dB of image and carrier rejection ratios. Comparison between the proposed technique and recently published state of the art schemes shows that the proposed technique outperforms existing techniques in terms of speed, performance, and practical use scenarios.