A 600 mV + 12 dBm IIP3 CMOS LNA with Gm Smoothening Auxiliary Path for 2.4 GHz Wireless Applications

Abstract

Linearity plays an important role in RF systems because nonlinearity issues comprise harmonic distortion, gain compression, cross modulation and intermodulation, etc. RF devices using 802.11b/g/n experience interference from other products operating in the 2.4 GHz band. Devices operating in the 2.4 GHz range include Bluetooth devices, cordless telephones, some radio equipment and wireless keyboards. As the first block in receiver, the LNA must be sufficiently linear to suppress interference due to intermodulation distortion and maintain high sensitivity. In realistic scenario, more than one interferer is going to interfere with the fundamental component causing intermodulation distortion. Interaction of higher-order harmonics and intrinsic second-order nonlinearities distorts the fundament frequency components. Second-order interaction with the fundamental frequency contributes to intermodulated components, which intern increases the overall nonlinearity. Hence overall second- and third-order nonlinearity contribution should be suppressed to increase the performance of the LNA. Derivative and modified derivative superposition methods are well known for offering more linearity in LNAs. With identified limitations of modified derivative superposition method, the simulated results are compared and summarized with the reported literature. A new inventive LNA model is presented in this work to improve the linearity with a little sacrifice in gain.