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Simulators >> RF Simulators >> How to set resistor of input port for Pnoise
https://designers-guide.org/forum/YaBB.pl?num=1052660826

Message started by tulip on May 11^th, 2003, 6:47am

Title: How to set resistor of input port for Pnoise
Post by tulip on May 11^th, 2003, 6:47am

When using Pnoise to calculate NFof mixer, To match the IEEE definition of noise figure, the input probe must be a port with no excess noise and its noisetemp must be set to 16.85C (290K).

My question is, Need I set the value of the resistor in Port to be 50 ohm? If not, what value I must set?

Title: Re: How to set resistor of input port for Pnoise
Post by pancho_hideboo on May 12^th, 2003, 9:53pm

> My question is, Need I set the value of the resistor in Port to be 50 ohm?
> If not, what value I must set?

If DUT is perfect linear, we can characterize NF with arbitrary source impedance
since we can get constant {NFmin, Sopt, Rn}. So in this case, you don't need to set it as 50ohm.

But for mixer, this is not true since local power will be leaked to RF port
then cause some amplitude in source impedance.
This amplitude in source impedance could perturb operation point of mixer.
Even though there is no local leakage, source impedance value could
change operation point of mixer due to nonlinear nature.

So for mixer, you should set source impedance closely as actual value such as
expected output impedance of image rejection filter or output impedance
of driver amplifier.
If you assume actual measurement using NF-meter without image rejection filter,
source impedance should be 50ohm. ::)