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Simulators >> RF Simulators >> iip2 of mixer
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Message started by karen on Sep 14^th, 2007, 10:15am

Title: iip2 of mixer
Post by karen on Sep 14^th, 2007, 10:15am

Hi
I am running mixer iip2 simulation with qpss. What is the maxharms of large signal(Lo) and small signal(two rf in) I should use?

I tried 1, 5, 10 for large signal and 1,2,3 for small signal, The difference of iip2 can be 40dB. More harmonics, the better iip2. I need at least 10 harmonics for large signal and 2 for small signals.

To my understanding, 1 for large signal and 1 for two small signals is good enough. Only noise simulation needs more harmonics for noise folding. How does the harmonics number influence the accuracy?

Title: Re: iip2 of mixer
Post by sheldon on Sep 16^th, 2007, 9:54pm

Karen,

Don't think that one tone of the LO or RF inputs is sufficient for simulating
the IIP2 of a stage. There are no simple rules for the number of tones to
use. If you run a transient and plot the LO signal does it look like the LO
signal plotted when from QPSS analysis? To accurately capture the non-
ideality of the LO may require many tones and using 10 tones is not an
unreasonable number of tones to use.

Other questions:
1) Are you relying on device matching to improve the IIP2, that is, canceling
the even distortion with differential circuits?

In this case you will need to model the effect of mismatch, that is, perform
Monte Carlo simulation

2) Have you tried using perturbation analysis to estimate the IIP2?

Best Regards,

Sheldon

Title: Re: iip2 of mixer
Post by karen on Sep 17^th, 2007, 3:54pm

Hi,Sheldon,
Thanks. I still don't understand how many harmonics should I use for two small input signals, I think 1 for each should be enough. What is your opinion?

2)I want to make sure the number of harmonics are chosen rightly, then I'll go to monte carlo.

2) what is the proposal to use perturbation analysis?

regards
keren :)

Title: Re: iip2 of mixer
Post by simon2 on Sep 23^rd, 2007, 12:49pm

Hi karen,
maybe I missed the point of your question, but should you not be thinking about a taylor series description of the signal waveform?

that is: the coefficents for each term f1+f2, f1-f2, 2f1+f2, f1+2f2 etc?

- therefore if your circuit becomes more non-linear under large signal conditions, you should be considering more terms according to how large each term is?

Cheers,
SimonH.