Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
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My Hobby Website:
IIP3 measurement - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
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