How do i calculate out the oip3 of the transmitter - RF Cafe Forums

 Post subject: How do i calculate out the oip3 of the transmitter

Posted: Wed Oct 10, 2007 9:19 am 

At the stage of system design of the cdma transmitter, how can i get the oip3 metric based on ACPR requirement defined in the 3gpp standard?
which some papers are about how getting the metric by calculating or simulation?

 Post subject:

Posted: Tue Dec 18, 2007 6:07 pm 

By looking at the standard, you should have a transmit mask. From here you can see what the required ACPR for your system will be. Once this is known and you know how many channels are in your system, you can get an approximate result for your required system OIP3. See [1].

Once this is known, you can figure out what each stage IIP3 needs to be based on the linear gain of each stage and what the signal levels are and from there you can back calculate all of the individual specifications for your blocks. The author of this paper has many other works on the same subject. Just do a Google Search and you will find more results.

Hope this helps.

-J

[1] N. B. Carvalho and J. C. Pedro, "Compact Formulas to Relate ACPR and NPR to Two-Tone IMR and IP3", Microwave Journal, Vol.42, N. 12, Dez. 1999.

 Post subject:

Posted: Wed May 14, 2008 3:41 pm 

I assume that you need a relationship between ACPR and IP3, so when you test the device, you don´t have to use a digital transmitter generator to know if you are meeting with the ACPR specs, and you want to meas the ACPR indirectly using the IP3.
What I can recommend is to always polish the designs with the digital signal and be sure to meet with the specs. Once you have this, you can characterize the amplifier measuring many points of it´s IP3 from the P1db to the point of your average power. This way, you will know the linearity of the peak to av zone of your amp, this zone is where the digital modulated signal will be and this is what will define your ACPR, you can´t predict an ACPR of a peaking signal with one IP3 point.

An Other way (slower):
I never did any simulation, but i know it can be done (not in a easy way), knowing the CCDF curve of your signal, the IP3 vs power characteristic of your amp and your desired avg output power, you will be able to simulate the ACPR responce... But it is very slow.. every change you do on the amplifier you will have to extract all the IP3 vs power data and enter it again on the simulator.

Hope this helps..