Calculate NF and Back-off in receiver chain

In a receiver chain some parameters should be calculated.

Chain: LNA, SAW, adj. Attenuator, ?, VGA.
Input signal min. -80 dBm, max. -40 dBm.

To calculate the NF, Back-off which conditions regarding gain should be adjusted. I think NF calculate at min. input level and max. gain.

Have you maybe some paper where such calculations are explained.

Regards,

Olzanin

check this link , lecture 11 , and 12 will answer ur question

http://inst.eecs.berkeley.edu/~ee142/fa04/

khouly

Sorry, I don't have access permissions!

Could you upload?

Regards,

Olzanin

i will upload the two lectures here


khouly

Slide 15 of Lecture 12 has the relevant equation. You are going to want to calculate the Noise figure with the minimum input signal.

The next step is to figure out what the output signal level's are. Typically, this is governed by the A/D Converter you are feeding. The VGA's in a receiver should be set to keep the input power to the A/D Converter below the maximum, with some margin. This point is where you would make the trade off between A/D Converter dynamic range and filter rejection.

At the maximum signal input level, You need to make sure that your receiver isn't operating in compression, and any interferers are low enough that you have enough SNR so that your sensitivity doesn't degrade.

Dave
www.keystoneradio.com