High gain low noise figure LNA circuit employing variable gain amplifier

This paper presents the realization of high gain low Noise Figure (NF) Low Noise Amplifier (LNA) employing the variable gain amplifier. The high gain is achieved by cascading three stages while the low NF is achieved by employing the resistive feedback in the input stage. The linearity is achieved by employing the source degeneration technique. The variable gain amplifier gets turned on/off by the input signal causing the change in the transconductance of the LNA and hence the gain of LNA varies according to the input signal strength. The results show that maximum gain for the realized LNA is 21.34 dB at 1.72 GHz for M7 ON position while during M7 OFF position, the maximum gain achieved is 26.05 dB at 1.72 GHz frequency. The S11 value is less than –9 dB for the frequency range of 1.65 GHz to 3.9 GHz, i. e., having the bandwidth of 2.25 GHz and it is matched for the 50 Ω termination at input and output port. The minimum value of the NF during low conductance is 2.88 dB while during the high conductance it is 2.82 dB.