Serendipitous noise reduction in inductively degenerated CMOS RF LNAs

The design of radio-frequency inductively-degenerated CMOS low-noise-amplifiers does not follow the guidelines for minimum noise figure. Nonetheless, state-of-the-art implementations achieve noise figure values very close to the theoretical minimum. In this brief contribution, we point out that this is due to the effect of the parasitic overlap capacitances in the MOS device acting as transconductor. In particular, we show that overlap capacitances lead to a significant induced-gate-noise reduction, especially when deep sub-micron CMOS processes are used.