A 1V, low power, high-gain, 3 – 11 GHz double-balanced CMOS sub-harmonic mixer

Design and simulation of a low power ultra wide band doubly balanced 2× sub-harmonic direct conversion mixer in a 0.18-μm CMOS technology is presented. The basic idea of the proposed mixer is adopted from the conventional Gilbert cell mixer, with two modifications incorporated. The first is that each of the switching quad transistors is replaced with a pair of transistors where their two drains, and also their two sources, are connected together (forming a “switching octet” instead of a “switching quad”). The signals driving the switching octet now has 4 different phases 0°, 90°, 180° and 270° (as opposed to the 2 phases 0° and 180° needed for the conventional Gilbert cell) which their waveform is in such a way that none of the octet transistors driven by different phases will be simultaneously on. These 4 driving phases are generated by a circuit block comprised of an 8-phase oscillator and 4 frequency doublers. The second modification is that each of the two transconductance transistors is replaced with an inductor. In the proposed mixer the RF signal is applied to the sources of the switching octet transistors. Because of this modification, stacking of transistors is avoided, allowing low voltage operation of the circuit. Simulation results performed using Hspice show The mixer draws 4.5 mA of dc current from a 1 V power supply, and achieves a bandwidth from 3 GHz to 11 GHz, a voltage conversion gain (CG) of 14~23dB, and 3^rd intermodulation intercept points (IIP3) of -1.2 dBm.