Design of On-Chip Inductors with Optimized Quality Factor for a 24 GHz LNA

A spiral inductor with nonuniform width is designed in a 130nm technology for 24 GHz applications. Using basic analytical equations the quality factor (Q) is optimized. Full wave 2.5D Electro Magnetic (EM) simulations performed with the commercial software Sonnet confirm the results of our analytical model. Furthermore, this structure proves to be more efficient in terms of Q in comparison to other classical structures, e.g. the conventional spiral inductor with uniform width, the stacked, as well as the shunt inductors. The EM simulations show that the Self Resonance Frequency (SRF) of the designed inductors is at least 3 times higher than the operating frequency of the LNA (24 GHz), so that parasitic capacitances can be neglected in the LNA design. Therefore, a first order approximation of the inductor using a series R-L lumped model suffices to model the broadband behavior of the LNA with very good accuracy.