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Questions about 《Accurate and Rapid Measurement of IP2 and IP3》 (Read 3063 times)
DiegoFan
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Questions about 《Accurate and Rapid Measurement of IP2 and IP3》
Sep 21st, 2015, 11:43pm
 
Thanks for sharing this good doc. It's very useful to me and I found this forum through this doc. I have questions about it.

1. Page7, it shows "Define po1 = (aα)^2 to be the output power at ω1," Why?  As I see, it should be " (aα+3cα^3/4+3cαβ^2/2)^2 showed in (25)
Huh
2.  Page5, Supposed, In(3), we only consider two-order terms(bu^2). In(4), we suppose α=β=A. So we can get all second order IM2 products:
DC: b*(A^2)
f1+f2:  b*(A^2)cos((w1+w2)t)
f1-f2: b*(A^2)cos((w1-w2)t).

My question is:  IM2 products are distributed against total IM2 power as:   50%(-3dB) at DC,  25%(-6dB) at f1+f2,  25%(-6dB) at f1-f2.   WHY?
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« Last Edit: Sep 22nd, 2015, 1:28am by DiegoFan »  
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Ken Kundert
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Re: Questions about 《Accurate and Rapid Measurement of IP2 and IP3》
Reply #1 - Sep 23rd, 2015, 10:39pm
 
1. you are correct, but the cubic terms will be small and are considered negligible compared to the linear term.
2. I don't understand your question. You went through the mathematics to get the distribution, and then ask why. The why is explained by the mathematics.

-Ken
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DiegoFan
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Re: Questions about 《Accurate and Rapid Measurement of IP2 and IP3》
Reply #2 - Sep 24th, 2015, 1:45am
 
Ken Kundert wrote on Sep 23rd, 2015, 10:39pm:
1. you are correct, but the cubic terms will be small and are considered negligible compared to the linear term.
2. I don't understand your question. You went through the mathematics to get the distribution, and then ask why. The why is explained by the mathematics.

-Ken


Thanks. Based on the former 2 questions:
1. If we can skip the the cubic and squared items, it means α,β<<1. Based on this premise, we can eliminate α,β and get the final formula which shows indepedence between iIP3 and α,β. Conversely, if α,β>1, α,β cannot be eliminated in the final formula so it means  iIP3 has some relation with α,β.

However I know my conclusion above should be wrong because iIP3 is the non-linearity parameter of circuit and it should be only decided by the circuit itself. Anyway I don't know in which derivation part I make a mistake?

2. I know how to get the mathematics. But I don't know what' the reason to get the conclusion(50%,25%,25%) based on these mathematics.

Sorry for my long questions. Thanks a lot!
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Ken Kundert
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Re: Questions about 《Accurate and Rapid Measurement of IP2 and IP3》
Reply #3 - Sep 24th, 2015, 2:49pm
 
1. No, it implies that c is small. In the regime where you measure IP3 the 3rd order component is always small compared to the first order component.

-Ken
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