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regarding iip3 and p1db

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chacha

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p1db curve

hi all,

what is the best way to fix up the extrapolation point to plot the IPN curves(say iip3).
usually we find the region having the slope 3 for the 3rd order intermodulation curve and taking the mid point of that we will fix the extrapolation point.

but unexpectedly, my 3rd order intermodulation curve is not having slope 3(it is varying between -5 and 2.5).

can any explain why this is so??
 

what is p1db

Start by checking linear relationship up to the 1 dB compression point, using a single carrier test. It shall look like the plot on page 1 in this document:

**broken link removed**

An explanation for your 3rd order intermodulation curve is not having slope 3 could be intermodulation between the two signal generators used for giving the two tone signal input. You should have a 10 dB attenuator at each signal generator's output in front of a high isolation power combiner.

What is the frequency separation between the two carriers?
 

thank you VSWR. the pdf u sent was very good.

i am attaching how my CP1 curve looks like.
it is linear till the 1 db compression point.

how to chose the extrapolation point for plotting the iip3??
the two input frequencies are seperated by 3MHz.
 

chacha
take care of what you are simulating.
If you look at left side of your plot, for a -80dBm input you got -190dBm(!!!!) of output, so your circuit is an attenuator (-110 dB!!) with poor linearity.
I think that you should correct your simulation parameters and/or results.
I hope it can help.
Mazz
 

yeah there is attenuation , is it a simulation of a mixer or what , and if it is a mixer , are u remeasuring the power of which harmonic the IF , or RF feed through

khouly
 

iam very sorry for that last attachment. this is the first time i am doing mixer design.

i was using 2 ports at the output. if i use a single port it is giving a different result.
this time its output power is -90dbm for a -80dbm rf input(taken at IF).
the conversion gain is 15db.

thank u....
 

dear chacha

how it is have a gain of 15 , and the input is -80 , and the output is -90 , this is attenuation , u need to get the gain the ouput should be -70 dbm


check ur simulation again

khouly
 

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