A New Analog-based LO Harmonic Rejection Technique with Tunable Notch Frequency


Department of Electrical and Computer Engineering, Babol Noshirvani University of Technology, Babol, Iran


An effective technique for mixer LO harmonic rejection in a SAW-less wideband receiver front-end is proposed. The proposed technique provides a tunable notch that can be placed at any frequency like mixer LO harmonics, to avoid the aliasing in baseband after mixing. An analog LC notch is used in a cascode transconductor, and it can reject one of the 3rd or 5th harmonics. This notch frequency is tunable using the bond wire inductors or fixed Gyrator-C active inductor, and a capacitor array, without any significant Power/Area overhead on overall system. Since the accurate value of inductance is not clear, a calibration circuit is proposed to tune this LC notch. This tuning phase runs in forground, and consumes very low additional power. This technique is used in a wideband receiver front-end. Post-layout simulation in 130nm CMOS results in an average 3rd harmonic rejection ratio of 36 dB. The overall circuit consums 34mW power and a has a noise figure of 3.4dB at 1GHz frequency.