IQ-imbalance and DC-offfset compensation in ultrawideband Zero-IF receiver

This paper presents two calibration procedures for ultra-wideband SDR Zero-IF receiver operating in 1 GHz to 6 GHz frequency range. The IQ-imbalance compensation procedure trained with an additional testing monochromatic signal and based on complex FIR filter allows Image Rejection Ratio (IRR) better than -65 dBFS over 600 MHz bandwidth. For DC-offset minimization a hybrid method based on AC coupling with very low cut-off frequency and DAC-controlled hardware balancer of ADC inputs was developed. The level of the DC component in the output spectrum after calibration is close to 70 dBFS. It was also examined how the performance of compensation varies over time after described procedures are completed.