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The noise figure of a low noise amplifier (LNA) is a function of the quality factor of its inductors. The lack of high-Q inductors in silicon has prevented the development of completely integrated complementary metal oxide semiconductor (CMOS) LNAs for high sensitivity applications like global system for mobile communications (GSM) (1.9 GHz) and wideband code-division multiple-access (W-CDMA) (2.1GHz). Recent developments in the design of high-Q inductors (embedded in low cost integrated circuit (IC) packages) have made single-package integration of RF front-ends feasible. These embedded passives provide a viable alternative to using discrete elements or low-Q on-chip passives, for achieving completely integrated solutions. Compared to on-chip inductors with low Q values and discrete passives with fixed Qs, the use of these embedded passives also leads to the development of the passive Q as a new variable in circuit design. However, higher Q values also result in new tradeoffs, particularly with respect to device size. This paper presents a novel optimization strategy for the design of completely integrated CMOS LNAs using embedded passives. The tradeoff of higher inductor size for higher Q has been adopted into the LNA design methodology. The paper also presents design issues involved in the use of multiple embedded components in the packaging substrate, particularly with reference to mutual coupling between the passives and reference ground layout.
Date of Publication: Feb. 2004