Noise Figure vs Collector current density relationship

[Faizan shafi]

hi

I have plotted a Noise figure of a common emitter amplifier with respect to the collector current. I would like to know why i am getting tis behavior what is the cause of it.

1- why is the noise figure going up to 2.1 when the collector current is zero.
Is it because when Ic is zero. the shot noise is zero but thermal noise is maximum. thermal noise does not depend on the collector current.

why does noise figure decreases first and then increases slowly with the increase in collector current. Any explanation will be appreciated and or if you could refer any material that will also be grateful. Thank you.

 

[FvM]

Keyword is "noise matching". For each source impedance there's a collector current with minimal noise. That's due to opposite current dependency of noise voltage and current density.

 

[G4BCH]

This explains it.

https://www.uio.no/studier/emner/matnat/ifi/INF5460/h16/undervisningsmateriale/f8-1p.pdf