Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: IIP3 measurement Posted: Sun Aug 28, 2005 3:53
I want to measure IIP3 of an amplifier in spice ( LTSpice
) , how can I measure it ? Please help me ,
Post subject: IIP3Posted: Sun Aug 28,
2005 9:49 pm
You will have to derive the IIP3 in much the same way
as you would measure it in a lab. (The "Distortion" calculation of SPICE
is basically worthless). You'll have to do (at least) two "Transient
Analyses". That means "at at least two different power levels", and
then use the FFT capabilities of LTSpice to measure the amplitudes of
the resulting 3rd order IM products. The more analyses you do, the better
your eventual curve-fitting exercise will be. Plot the level of the
3rd order IM products as a function of the input power, and estrapolate
to the IIP3. This will be a regression analysis if you use more than
two points. And, of course, it's usually plotted in dBm vs dBm (which
makes it a log-log curve as far as power in Watts is concerned).
You will need an accurate model of your active device(s) - not all
available models will give you realistic results.
I hope this