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Design >> RF Design >> noise figure of passive circuit
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Message started by VNF on Jul 14^th, 2015, 11:21pm

Title: noise figure of passive circuit
Post by VNF on Jul 14^th, 2015, 11:21pm

Hi,

It is shown in multiple places that noise figure of a passive circuit equals to the power loss.

My question is, theoretically (assuming no bandwidth issue), if the network is a simple capacitor divider, i.e. with voltage gain of 1/2, then the signal, along with the noise will scale by 1/2 altogether, therefore SNR_out should be the same as SNR_in, which leads to NF = 1.

so what am I missing here?
thanks,
VNF

Title: Re: noise figure of passive circuit
Post by bellona on Jul 18^th, 2015, 9:31pm

The CAP divider is actually a impedance transformer, and ideally it introduces no power loss (Voltage halved with Current doubled), so the NF should be 0dB (F=1)

Title: Re: noise figure of passive circuit
Post by baohulu on Jul 23^rd, 2015, 11:59pm

I think you are right