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.