Design considerations for CMOS low-noise amplifiers

A low-noise amplifier is the first active stage of a CMOS RF receiver. The inductively degenerated common-source LNA (CS-LNA) topology is currently popular because it achieves high gain, low noise figure, etc. The amplifier´s performance is reviewed and the optimum Q value that gives the minimum noise figure is derived. It is then compared to the conventional common-gate LNA (CG-LNA) in terms of gain, noise figure, input matching, reverse isolation and stability. Finally, a general g_m-boosted design technique for common-gate RF circuits is introduced that provides lower noise figure and power consumption than the conventional CS-LNA and CG-LNA stages; it also preserves the CG-LNA insensitivity to parasitic input capacitances. In view of CMOS scaling, the CG-LNA topology is attractive for future higher frequency and/or lower power designs.