Analysis of NF of LNA, when operated beyond 1-dB

[kamranraja222]

Hello everyone,
I am analyzing that how the NF of LNA affects, when LNA is operated in saturation region. According to theory, NF should degrade. But in practice, when I measured LNA's NF by using spectrum analyzer, the SNR(out) remained at same level. Experts please throw some light on this issue.Thanks

 

[SLK001]

The noise floor of the SA is way higher than the noise floor of your LNA, so what you are seeing is the noise floor of the SA. Get a dedicated noise figure meter and source and retest.

 

[kamranraja222]

Thanks for the reply. When I varied input signal from-70dbu to 100dbu, the output power level and noise level is also varied accordingly(means output SNR varied) and this was shown on spectrum.However near saturation and beyond saturation level the output power level and noise level remain unchanged. The gain of the amplifier is 26. Unfortunately the only thing I have is spectrum and signal generator.