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iip3 of the attenuator from cadence

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shanmei

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The attenuator is built with ideal resistor as shown here:
1.png

The two input signal are f1=1GHz and f2=1.1GHz respectively, and the input power is -30dBm for both input signal.
2.png[
Run QPSS, the result is that:
3.png

At 1G and 1.1G, the spectre are both -33dBm, that' correct. (Input is -30dBm, and attenuation is 3dBm, so it is -33dBm.)
For the modulation signal: 2*f1-f2=0.9G, and 2*f2-f1=1.2G, why the amplitudes of the two modulated signals are quite different? Thanks.
 
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Attenuator is linear perfectly.
So there is no distortion.

0.9GHz : -150dBm
1.2GHz : -350dBm

These are almost zero.
So they are same value.

What analysis engine do you use as QPSS, Shooting-Newton or HB ?
I think you use Shooting-Newton-QPSS.

Dynamic range of spectrum from shooting-newton based analysis is far less than 80~90dB.

And treatments of f1 and f2 are different in Shooting-Newton-QPSS.
f1 is a large signal.
f2 is a moderate signal.
 
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Your analysis should show a perfectly linear attenuator. I believe your problem lies with the size of the steps that the analysis engine uses - it is probably too coarse to give you equal sidebands. You might want to see if you can change the step size (but it will cost you time).
 
Yes, I used newton before.

Now I changed to HB , and it works. The two modulated signals' amplitude are the almost the same now. Thanks.


The "size" option means conservative, moderate and liberal from qpss setting. Thanks.
 

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