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Type: Posts; User: sutapanaki

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  1. Closed: Re: Netlist is different between schematic and layout

    I guess you will have to provide more information. Like schematic, netlists, show how different the results are, etc. In a MOS transistor divider, interchanging drain and source shouldn't really be a...
  2. Closed: Re: Active and inactive dummy transistors in the matched array transistors

    This is a one possible layout. Or you can put all of M3 in one OD and all of M4 in another and don't interdigitize or common-centroid M3 and M4. Then you can have one dummy that bridges the two...
  3. Closed: Re: Active and inactive dummy transistors in the matched array transistors

    You can still share the drains and connect the gates to ground. Why not. That should be a perfectly legitimate way to do it.



    Yes, for the bottom transistors. For the cascodes the dummies have...
  4. Closed: Re: Active and inactive dummy transistors in the matched array transistors

    Scheme 3 only works well if you combine for example M1-M3 in a cell and abut them - for example you have one finger of M1, say S-D and then 1 finger of M3 like S-D and you abut them so it becomes...
  5. Closed: Re: Active and inactive dummy transistors in the matched array transistors

    Same OD means you put the active and dummy transistors in the same diffusion. I suppose you lay them out with fingers and something like S-D-S-D-S. If this is the case then you need to have a common...
  6. Closed: Re: Active and inactive dummy transistors in the matched array transistors

    You need to have a common net between the dummy and the active transistors, because the dummies need to be in the same OD as the active MOS. But having a common node doesn't necessarily mean having a...
  7. Closed: Re: Different transistor orientation in different matched MOS array

    If I understood well, you want not only the transistors within the individual arrays to be matched but also the arrays themselves to be matched with each other. Then if this is the case, you better...
  8. Closed: Re: Controlling partial or the whole current in CMFB

    I don't think 25% is a good idea. 50% is ok. 100% may not be a good idea too. Suppose you control 100% through the CMFB. What will happen if the CMFB doesn't start properly or for one reason or...
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    Closed: Re: Maximum current of the CMFB circuit

    When you say mismatch, what mismatch do you mean?
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    Closed: Re: Maximum current of the CMFB circuit

    Yes, the second one has more gain and hence can adjust the CM voltage for less input difference with respect to the CM ref. But you have to see how many poles you accumulate in the CMFB loop and if...
  11. Closed: Re: CMFB biasing current in fully differential Opamp with adaptive current source

    Yes, if the output common-mode voltage is half way to its settling value it will be probably a disaster. That's why I mentioned in my previous post that if it settles to within few mV of its final...
  12. Closed: Re: CMFB biasing current in fully differential Opamp with adaptive current source

    There are different opinions on how fast the CMFB circuit has to be. I've seen anything ranging from same speed as the main amplifier down to about 30% of the speed of the main amplifier. Especially...
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    Closed: Re: Gain and Phase margin problem

    It will be very helpful if you show your latest schematic, together with the CMFB, the way you break the loop and the plots of your results. Also, if you can back-annotate the DC operating point on...
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    Closed: Re: Gain and Phase margin problem

    From what I see, you've got no phase margin - 0deg or even negative, not quite visible from the plot.
    Two comments. You have a fully differential amplifier but i don't see you using a common mode...
  15. [SOLVED]Closed: Re: LoopGain analysis with multiple feedback loop

    Yes, as FvM said, that's the reason. Shunt feedback at the output reduces the impedance but only for as long as the loop gain is high. Once the loop gain dies with frequency, there is nothing else to...
  16. [SOLVED]Closed: Re: LoopGain analysis with multiple feedback loop

    Here is my opinion about what is happening here based on the discussion you guys had above. Say you check the loop stability of the top amplifier. The bottom amplifier presents a pretty low output...
  17. Closed: Re: Equivalent feed back model transformation

    Why don't you just use return ratio for the loop? Then you don't have to bother with the miller cap as it effect will be included in the ac gain of the OTA.
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    Closed: Re: Finding the input impedance of CCCS

    Yes, I read it. That's not a problem. I'm not saying other derivations are wrong, I said mine was correct and simple. Also, the result is arranged in a useful for design purposes way without need for...
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    Closed: Re: Finding the input impedance of CCCS

    Well, it is very easy to verify. Just build a simulation schematic with ideal vcvs for the amplifier, put a large gain, look for the input impedance and check the expressions against simulation....
  20. Closed: Re: Finding W and L of transistors from DC operating point.

    Wouldn't it be easier to just design the circuit yourself such that at least it produces the same gm and Vdssat, gain for the bias currents that you see on the picture?
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    Closed: Re: Finding the input impedance of CCCS

    Looks to me the shortest solution was given in #5
  22. Closed: Re: indivisual out different from differential output in fully differential amplifier

    It is common that in fully differential circuits you work with half circuite. Then it doesn't really matter if you talk about single ended or differential amplifier.
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    Closed: Re: Finding the input impedance of CCCS

    Pretty immediate in this case. The output resistance with feedback removed is R1, the loop gain with port (terminals of RL) shorted is A and the loop gain with port open is 0. The result is R1*(1+A).
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    Closed: Re: Finding the input impedance of CCCS

    Applying Blackman's impedance formula gives the output impedance in 1 line. And yes, it is R1*(1+A)
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    Closed: Re: Finding the input impedance of CCCS

    Yes, you can choose another element as the extra element, of course. The formulation of the result will be different, because you will have to find Rn and Rd from the point of view of the new extra...
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