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Aug 12th, 2020, 10:12pm
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 Questions about 《Accurate and Rapid Measurement of IP2 and IP3》 (Read 3341 times)
 DiegoFan New Member Offline Posts: 2 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) 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? Back to top « Last Edit: Sep 22nd, 2015, 1:28am by DiegoFan »     IP Logged
 Ken Kundert Global Moderator Offline Posts: 2277 Silicon Valley 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 Back to top IP Logged
 DiegoFan New Member Offline Posts: 2 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! Back to top IP Logged
 Ken Kundert Global Moderator Offline Posts: 2277 Silicon Valley 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 Back to top IP Logged
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