Efficient Compensation of IQ-Impairments in Direct Conversion Receivers

IQ-impairments, i.e. gain- and phase imbalance and DC offset, are significant sources of modulation errors in direct conversion transmitters. By means of careful circuit design the absolute impairment values can be kept low. However, in combination with digital predistortion for power amplifiers (PA's) which accounts for memory effects in the PA, even small values of IQ impairments can render the predistortion ineffective. We propose an IQ impairment estimation and compensation method which uses a simple detector diode in the feedback path. The characteristic of the detector diode needs not to be known, which makes implementation easy. It is shown by simulation and measurements, that the method works excellent for narrowband as well as for wideband signals.