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Design >> RF Design >> Intermodulation
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Message started by myjasonlee on Feb 12^th, 2005, 6:36am

Title: Intermodulation
Post by myjasonlee on Feb 12^th, 2005, 6:36am

Hello Everyone

I wish to clarif with you about the following topics;

If the input signal is coming in with two closely spaced channels, say at ω and
ω + δ, then the third order IM terms of interest are

2 ω - ( ω + δ ) = ω - δ

and

2 ( ω + δ ) - ω = ω + 2δ

My question is, are both of these frequencies important for IM distortion, or is it only the first one, which is nearest to ω that causes problems ?

For multitone input, say N tones, each spaced by δ, so that we have ω, ω + δ,
ω + 2 δ, ω + 3 δ, ..., ω + N δ, we will get many 2 tone and 3 tone IM products

2 (ω + i δ) - ( ω + j δ ) = ω + ( i - j ) δ

and

(ω + i δ) + ( ω + j δ ) - (ω + k δ) = ω + ( i + j - k )δ.

Are the only terms of interest for IM3 the ones where

i - j = ± 1

and

i + j - k = ± 1 ?

Thanks

Jason and Tel

Title: Re: Intermodulation
Post by myjasonlee on Feb 12^th, 2005, 6:40am

Sorry there are some problems.
Kindly refer to the below corrected question..........
Thank you

========================================
Hello Everyone

I wish to clarify with you about the following topics

If the input signal is coming in with two closely spaced channels, say at w and
w + delta , then the third order IM terms of interest are

2 w - ( w + delta ) = w - delta

and

2 ( w + delta ) - w = w + 2delta

My question is, are both of these frequencies important for IM distortion, or is it only the first one, which is nearest to w that causes problems ?

For multitone input, say N tones, each spaced by delta , so that we have w , w + delta ,
w + 2 delta , w + 3 delta , ..., w + N delta , we will get many 2 tone and 3 tone IM products

2 (w + i delta ) - ( w + j delta ) = w + ( i - j ) delta

and

(w + i delta ) + ( w + j delta ) - (w + k delta ) = w + ( i + j - k )delta .

Are the only terms of interest for IM3 the ones where

i - j = ± 1

and

i + j - k = ± 1 ?

Thanks

Jason and Tel