A 400-to-900 MHz receiver with dual-domain harmonic rejection exploiting adaptive interference cancellation

Wideband direct-conversion harmonic-rejection (HR) receivers for software- defined radio aim to remove or relax the pre-mixer RF filters, which are inflexible, bulky and costly. HR schemes are often used, but amplitude and phase mismatches limit HR to between 30 and 40 dB. A quick calculation shows that much more rejection is wanted: in order to bring harmonic responses down to the noise floor (e.g. -100 dBm in 10 MHz for 4 dB NF), and cope with interferers between -40 and 0 dBm, an HR of 60 to 100 dB is needed. Also in terrestrial TV receivers and in applications like DVB-H with co-existence requirements with GSM/WLAN transmitters in a small telephone, high HR is needed. In this work, an architecture aiming for >80 dB HR is shown. It consists of an analog front-end followed by adaptive interference cancellation (AIC) in the digital domain. AIC is known for its ability to adapt to and mitigate unknown system non-idealities, e.g. gain and phase imbalances. Due to its adaptivity it can achieve large improvements, provided the interference estimate is accurate. To the authors´ knowledge, they are the first to explore AIC for HR and previously presented simulation results. Here a new and different architecture and measured results with the RF part implemented in 65 nm CMOS and the AIC in software are presented.