Design considerations and experimental results of continuously-tuned reconfigurable CMOS LNAs

This paper analyses the use of continuously-tuned Low Noise Amplifiers (LNAs) for the implementation of the next generation of software-defined radio receivers. Two LNA circuits are discussed. One is based on a folded cascode stage and the other one consists on a two-stage inductively degenerated common-source configuration. Both LNAs - designed and implemented in a 1-V 90-nm CMOS technology - employ MOS-varactor based tuning networks to make the operating frequency continuously programmable within the band of interest, targeting the requirements of GSM, UMTS, Bluetooth and WLAN standards, as well as any other operation mode in between. Practical design issues are presented, considering the effect of circuit parasitics associated to both the chip package and integrated inductors, capacitors and varactors; as well as technology parameter deviations. Experimental measurements demonstrate a correct operation of the circuits, showing a continuous tuning of Noise Figure (NF) and S-parameters within a 1.75-2.48 GHz band, featuring NF <; 3.7 dB, S₂₁ >;19.6 dB and IIP3 >; -9.8 dBm in a frequency range of 1.75-2.23 GHz.