IP2 point extrapolated from IP3 point

[Fran Fogarty]

Hi Guys, new to this forum.
i was wondering is there a relationship between IP3 and IP2. so that you could estimate IP2 based on a measured IMD3 value and an approx IP3 point value?
Regards

 

[ltrlspree]

Hi,

just researching about this point myself and it does not seem possible from the docs I found.

Only found this paper,
http://www.signalpro.biz/pointsf1.pdf
Where they show below rule of thumb
IP2 = 1dBCP + 27 dB ( sigma = 8.1 dB)

However I d not trust it, there is also a similar rule of thumb between IP3 and P1db which in the practice does not seem to work in my experience.

BR
Carlos

 

[vfone]

There is no direct relationship between IP2 and IP3 (or between IM2 and IM3), the same as for example, there is no direct relationship between 2nd harmonic and 3rd harmonic of an amplifier.

In case of two-tone input signal if you relate to the fundamental level (f1 and f2), IM2 increase 2dB for 1dB increase of the fundamental, and IM3 increase 3dB for 1dB increase of the fundamental. These are valid only if the amplifier is not in saturation.