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.