Enhanced-Selectivity high-linearity low-noise mixer-first receiver with complex pole pair due to capacitive positive feedback

A mixer-first receiver with enhanced selectivity and high dynamic range is proposed, targeting to remove SAW-filters in mobile phones and cover all frequency bands up to 6 GHz. Capacitive negative feedback across the baseband amplifier serves as a blocker bypassing path, while an extra capacitive positive feedback path offers further blocker rejection. This combination of feedback paths synthesizes a complex pole pair at the input of the baseband amplifier, which is up-converted to the RF port to obtain steeper RF-bandpass filter roll-off and reduced distortion. This paper explains the circuit principle and analyzes receiver performance. A prototype chip fabricated in 45nm Partially Depleted SOI technology achieves high out-of-band linearity (IIP3=39 dBm, IIP2=88 dB) combined with sub-3 dB noise figure. Desensitization due to a 0-dBm blocker is only 2.2 dB at 1.4 GHz.