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Design >> RF Design >> How to calculate the out band of IIP3 in communication system?
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Message started by spring on Sep 9^th, 2009, 10:32pm

Title: How to calculate the out band of IIP3 in communication system?
Post by spring on Sep 9^th, 2009, 10:32pm

Hi, everyone,
In communication system, when there are blocks in N+2 channel and N+4 channel, how to calculate the out band of IIP3, I read a paper"A direct-conversion receiver for DVB-H" it says IIP3=(2Pd+Pa+G-IMD3)/2, I do not know how this formula derived, any one can give me some analysis. thank you:)

spring

Title: Re: How to calculate the out band of IIP3 in communication system?
Post by aaron_do on Sep 16^th, 2009, 5:16am

Hi,

first I assume you are trying to calculate the required IIP3, not the IIP3 of some circuit block. You don't need the blockers to be in the N+2 and N+4 channel, N+1 and N+2 will do. The 3rd order output will be

y₃ = Bx³
10log(y₃) = 30log(x) + 10logB

the first order is

y₁ = Ax
10log(y₁) = 10log(x) + 10log(A)

From here its pretty straight forward. IIP3 is the value of x where y₁ and y₃ are equal. The gain is of course equal to 10log(A). you can substitute the powers in the N+1 and N+2 channels in y₃.

cheers,
Aaron