cascaded ip3

Hi,
Who can help me derive the formula 1/ip3_total=1/ip31+G1/ip32?
Thank you very much!

Added after 7 minutes:

I find it in RF Microelectronics,page 24.

Hi

I think it is derived in Pozars "Microwave and RF Wireless Systems ".

Do not remember which chapter.

Regards

use the APPCAD to do it ,it a free software from the www.avagotech.com,it is easy

Hy

imd_tot=imd1*G2+imd2 (worst case)
where imd is amplitudes of imd products on the stage outputs
ip3=P^(3/2)/imd^(1/2)
so

1/ip3tot=(P1^(3/2)/ip3.1*G2+(P1*G2^2)^(3/2)/ip3.2)/(P1*G2^2)^(3/2)=
=1/ip3.1/G2^2+1/ip3.2

Do I need to consider the phase of each block in the IIPS calculation?

use the APPCAD to cal

Hi
The up noted formula based IP3 calculation is not exact.
It is worst case calculation.
The phase is not taken in to account.

Hi
APPCAD is a really useful software.
Thx a lot

Well, the thing is that
I'm trying to use to phase difference of each block to add or cancel my gain and IMD.
Should I calculate them in S domian
Or is there any better way to work on this issue?

Waveman~

Hi
If You need ip3 calculated agree well with measured
You need take stages mismatch and input and output impedance nonlinearities
So use circuit simulator and full stages nonlinear model.
Regards

thx grig

thx everyone

speaking of intermodulation product, my teacher told us that the last stage is always more important. Why is that?

That is not always true. If you are striving for a given output power, such as 10 mW, and all the amplifier stages in a chain are driven by the same power supply voltage, say 3 V, then obviously the last amplifier in the chain is operating the closest to its saturation point. The more saturated an amplifier, the more it contributes to the overall chain's OIP3.

However, if you are talking about a receiver with various filters, mixers, variable attenuators in AGC loops, etc, you do have to be careful to look at each element in the chain at various input power settings. Sometimes there is one AGC setting that stresses another part mid way up the chain.

usually the last stage determine the linearity , so usually the last amplifier(PA) have a restrict linearity requirement!