The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> RF Design >> IM3 --> IP3
https://designers-guide.org/forum/YaBB.pl?num=1102047220

Message started by Jeffrey on Dec 2^nd, 2004, 8:13pm

Title: IM3 --> IP3
Post by Jeffrey on Dec 2^nd, 2004, 8:13pm

What is the relation between IM3 (3rd order intermodulation component) and IP3 (third-order intercept point)? How do I convert from IM3 to IP3?

Title: Re: IM3 --> IP3
Post by Andrew Beckett on Dec 2^nd, 2004, 9:54pm

The IP3 "tree" looks like this:

	\|	\|
	\|	\|
\|	\|	\|	\|
\|	\|	\|	\|
IM3₁	IF₁	IF₂	IM3₂

If the input power is P_in, then the input referred IP3 is
P_in+(IF₁-IM3₂)/2
or
P_in+(IF₂-IM3₁)/2

This is fairly obvious if you plot the intercept point, since the IF's will increase at 1dB/dB and the IM3's will increase at 3dB/dB (assuming no compression, which is how the intercept point is computed).

I just remembered that this is covered in Ken's paper:
http://www.designers-guide.com/Analysis/intercept-point.pdf

Regards,

Andrew.

Title: Re: IM3 --> IP3
Post by hrkhari on Dec 18^th, 2004, 9:41pm

Hi Guys:

Which value is significant in active mixer design, IIP3 point or OIP3 point, in my design of mixer I obtain an IIP3 point of 13.39dBm but a corresponding output OIP3 point of -21.07dBm, I understand that the IIP3 point should be as high as possible to alleviate the IM3 distortion, how does OIP3 signify?. Thanks in advance

Rgds

Title: Re: IM3 --> IP3
Post by maserati on Jan 26^th, 2005, 4:20pm

In your case, it sounds like the IN->OUT signal path has about 35dB gain.
If the gain is fixed, the IIP3 and OIP3 basically is same, theoretically.
However, if the Gain veries, the IIP3 will change as well.