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

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.