The self-calibration method of IR mixer with low IF

This paper describes a new self-calibration method of phase shifters providing better suppression of image component in the signal path of a receiver for ISM 2.4 GHz band. The method has been applied to Hartley architecture of image-reject mixers that are used in low IF RF receivers. The method relies on measuring the amplitude differences and phase errors between the I/Q mixer signals and iterative tuning of digitally controlled capacitance arrays, which are located inside the phase shifters. Circuit implementation of the proposed method in 0.35 μm BiCMOS provided IRR (Image Rejection Ratio) = 45 dB what is about 20 dB better than IRR obtainable without self-calibration. The range of amplitude compensation is 20% and the phase correction operates correctly in the range of initial phase error ±4°.