The wide variety of applications and the consumer demand for higher data rates has led to the emergence of newer wireless communication standards, usage of different frequency bands, and latest modulation schemes. This demands a multistandard unit that should be flexible to cope up with the existing and newly launched wireless communication standards. Such a unit is termed as a Software-Defined Radio (SDR). For portability and affordability, this unit needs to be cost effective, smaller, and consume low power. The CMOS technology, which is low-cost, highly integrable, consumes relatively small power, achieves extremely high speed, is a suitable option for the design of multistandard radio devices. The research in this thesis focuses on the design of CMOS based LNAs, suitable for flexible radio terminals like Software-Defined Radio. Three low-noise amplifier RFIC''s are realized of which the first two are designed in 130 nm CMOS technology from IBM, while the third is designed in 150 nm CMOS technology from LFoundry. A novel, stacked connection of CG Amplifiers is proposed to achieve wideband input matching. Stacking allows an input matching at half the transconductance and current, in contrast to the conventional common-gate LNAs. Results depict a high gain, 2 GHz of bandwidth, small NF with extremely low power consumption. A novel, low-power, current-reuse, noise-cancelling, UWB LNA, which utilizes only two individually biased stages, is proposed. This LNA performs noise cancellation to break the tradeoff between the input matching and the noise figure, in addition to providing the 50 Ω output matching for measurement, without the need of an additional buffer. In the first IC tape-out, a novel and extremely simple FDC technique is proposed, which includes a diodeconnected transistor in the feedforward network. The diode-connected transistor generates third-order distortion components in an opposite polarity with respect to those produced by the main amplifier. As a result, the third-order intercept point is improved. This LNA finds application in tunable multistandard radio receivers. In the second IC tape-out, a modified resistive shunt feedback LNA is proposed and analyzed. The proposed LNA, with an active feedback, performs noise and distortion cancellation to improve the noise figure, and the third-order intercept point, in contrast to a resistive shunt architecture. Detailed mathematical analysis for the modified input impedance, noise, and distortion-cancellation are presented with the measured results. In the third IC tape-out, a low-power LNA is proposed for MIMO and Phase Array applications. It is the first ever implementation of a positive feedback CG LNA in a single-ended configuration, which avoids balun thus, saves chip area, cost, and does not degrade receiver''s sensitivity. It is demonstrated mathematically for the first time that positive feedback can partially cancel the noise of the input matching CG transistor. Novel analysis for the LNA is performed using the return ratio concept. The wideband, low-power, low-noise, and highly linear LNAs proposed in this research, pave the way towards the implementation of a multistandard Software-Defined radio.