MOST Moderate–Weak-Inversion Region as the Optimum Design Zone for CMOS 2.4-GHz CS-LNAs

In this paper, the MOS transistor (MOST) moderate-inversion (MI)-weak-inversion (WI) region is shown to be the optimum design zone for CMOS 2.4-GHz common-source low-noise amplifiers (CS-LNAs) focused on low power consumption applications. This statement is supported by a systematic study where the MOST is analyzed in all-inversion regions using an exhaustive CS-LNA noise-figure (NF)-power-consumption optimization technique with power gain constraint. Effects of bias choke resistance and MOST capacitances are carefully included in the study to obtain more accurate results, especially for the MI-WI region. NF, power consumption, and gain versus the inversion region are described with design space maps, providing the designer with a deep insight of their tradeoffs. The Pareto-optimal design frontier obtained by calculation-showing the MI-WI region as the optimum design zone-is reverified by extensive electrical simulations of a high number of designs. Finally, one 90-nm 2.4-GHz CS-LNA Pareto optimal design is implemented. It achieves the best figure of merit considering under-milliwatt CS-LNAs published designs, consuming 684 μW, an NF of 4.36 dB, a power gain of 9.7 dB, and a third-order intermodulation intercept point of -4 dBm with load and source resistances of 50 Ω.