Abstract
The design issues in designing low noise amplifier (LNA) for Software-Defined-Radio (SDR) are reviewed. An inductor-less wideband low noise amplifier aiming at low frequency band (0.2-2 GHz) for Software-Defined-Radio is presented. Shunt-shunt LNA with active feedback is used as the first stage which is carefully optimized for low noise and wide band applications. A digitally controlled second stage is employed to provide an additional 12 dB gain control. A novel method is proposed to bypass the first stage without degrading the input matching. This LNA is fabricated in a standard 0.18 mu m CMOS technology. The measurement result shows the proposed LNA has a gain range of 6 dB-18 dB at high gain mode and -12 dB to 0 dB at low gain mode, as well as a -3dB bandwidth of 2 GHz. The noise figure (NF) is 3.5-4.5 dB in the high gain setting mode. It consumes 20 mW from a 1.8 V supply.