aaron_do wrote on Apr 13th, 2012, 1:54am:Hi Song,
I don't really understand your question. If you change the frequency, the results can definitely be different, especially if the gain is different at the new frequency.
regards,
Aaron
Hi Aaron,
I am sorry I did not clearly express my thinking.
Supposing the amplitude of the input two tones at f
1 and f
2 are x
1 and x
2, respectively. And the output tones at 2f
2-f
1 (f
IM3), f
1 and f
2 are P
IM3, P
1 and P
2, respectively.
If we use the fundamental tone at f
1 in the calculation,
for log-magnitude response,
P
1 = x
1 + b
0P
IM3 = x
1 + 2x
2 +b
1We can have IIP3 = (P
1-P
IM3+2x
2)/2;
However, if we use the fundamental tone at f
2 in the calculation,
for log-magnitude response,
P
2 = x
2 + b
0’
P
IM3 = x
1 + 2x
2 +b
1We can have IIP3’ = (P
2-P
IM3+x
1+x
2)/2;
IIP3 and IIP3’ are equal only if the gain at f
1 and f
2 are equal, which may not be true for all systems.
I hope the aforementioned explanation can make my question clearer. Thank you.
Best Regards,
Song