third order intercept
I want to measure third order intercept of my LNA in ADS2003A.What is a proceedure.
Third order intercept point is a measure how linear a power amplifier is. Since you design a LNA you don't have to simulate the intercept point.
The linearity of LNA also is important because there are large blockers and interferes in communication environment.
The large blockers can desensitize the nonlinear LNA, and the adjacent or alternate channel of the large interferers can corrupt own channel.
You can get the fundamental concept of intercept point at below link.
http://www.odyseus.nildram.co.uk/Sys.../Linearity.pdf
Regards.
When the input signal (at frequency f0) of the amplifier is high, at the amplifier output you find not only the input frequency f0 but its harmonics also, 2*f0, 3*f0,.....
The amplifier shows a non linear behaviour, in first approximation you may write the output signal as a function of the input signal in this way:
y = A [ x + k2 * x^2 + k3 * x^3]
With this simple model you observe the compression phenomenon that may arise.
With 2 different frequencies (f1 & f2) at the input of the amplifier you 'll find other unwanted frequencies at the output such as (2*f1-f2) and (2*f2-f1).
These frequencies tones are called 3 order intermodulation products and they are very troublesome because they are very near to the input frequencies f1 & f2 and they can't be deleted with a filter.
You may quantify the intermodulation with the 3rd order intercept point (IP3) : the input power that give you the intercept between the Pout (f1) (in the linear behaviour) and the Pout (2f2-f1) (see the picture in the attachment).
In a Low Noise Amplifier the input signal is so small the you have not any non linear behaviour.
Hi,
This point was discussed a lot of time. Try a search on edabord. See one of the topics :
h**p://www.edaboard.com/viewtopic.php?t=70959&highlight=ip3
* = t
ur request explained well at gonzaliz book at chapter of power amplifier
regards.the interceipt point is used to study the interceipt(interference) of (2f1-f2)or (2f2-f1) where f1 and f2 input to amplifier at gae and source or at base and emitter,inoher ward study the isolation of any harmonics about the fundamentals(f1,f2,f1-f2,f1+f2)
regards