Variable gain broadband low noise amplifier using tunable active inductor

The variable gain broadband low noise amplifier (LNA) is presented in this paper using tunable active inductor (TAI). The active inductor is adopted instead of feedback spiral inductor in the intermediate amplification stage to achieve variable gain and extend bandwidth. Furthermore, a high gain push-pull inverter with the feedback resistor is employed to realize a good trade-off between wideband matching and low noise figure (NF) in the input stage. At output stage, a source follower structure is adopted to achieve good output impedance matching. The LNA is verified by Advanced Design System (ADS). The results show that over the range of 0.5 GHz-5.5 GHz, the gain can be tuned from 15.5 dB to 19.6 dB, input and output return loss are better than -10 dB, the NF is less than 5 dB, and the total chip size is reduced dramatically.