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How to measure NF in the Zero -IF structure

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mitgrace

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Dear All :

We are measure the Zero-IF structure, The I /Q out form mixer, We using two port to measure N.F. one port is LNA input , another port is I/Q . But I have somequestions, Because the I/Q is from DC to BW. How Do I do that ? The Noise Figure meter is always Fmin is 10MHz. Does anyone have these experiments ? Thanks
 

You are using instrument or simulator to measure it?
 

You can use two different method:

1) you can apply directly the definition of NF=(S/N)in/(S/N)out => -G -Ni + No
where G = gain, Ni = -174 dBm/Hz, No is the noise in the oputput measured with a spectrum in dBm/Hz.
2) you can use directly the Y-method. You can simply find it in Agilent application note.

The method 2) is better, because you remove the systematic error. I think that you should use the two method and compare the results.
 

Sounds like you are using an HP 8970 to measure your NF. You can use the noise source from it to perform method 2) recommended by dinone. See the note from Maxim below:

hxxp://www.maxim-ic.com/appnotes.cfm/appnote_number/2875
 

I forgot to inform you that when you perform the measurements with the two different mode you will try a difference of 3 dB (the method 1 is higher of 3 dB than the method 2). This is because the method 2 is a measurement that, for how is performed, don't consider the image frequency, because you perform two noise measurements with the image placed over, and, since the Y method is a ratio of two noise the image is eliminated. In the method 1 usually you consider the gain sending a singol tone without its image, instead you will measure the noise with its image. So you will try a results 3 dB higher.
 

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