Abstract
The main design goals of an LNA are to achieve low noise figure, high gain, good linearity and good matching and reverse isolation. The choice of the LNA topology is therefore very important to suit the design application. Five LNA topologies were studied, analyzed and compared in this chapter. The topologies are the Simultaneous Noise and Input Matching (SNIM), Power-constrained Simultaneous Noise and Input Matching (PCSNIM), Current-reuse (CR) and Folded-cascode (FC) LNAs. The last topology is the PCSNIM with buffer. The circuits are analyzed in detail in terms of their functionality and compared based on the LNAs typical performance metrics. From the analysis, the PCSNIM technique can improve matching and noise performance of the inductively degenerated cascode. The current-reuse is found to consume less current but maintaining the circuit’s transconductance to achieve the desirable gain. The folded-cascode operates at lower voltage and hence is suitable for low-powered designs. Consequently, it is also resulting in the lowest noise-figure amongst the other designs.
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