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  1. #1
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    folded cascode with gm/id

    Hello i am trying to follow the instructions in the attached article for the circuit shown bellow.
    At the third page we see that I1=40uA from the ft ,SR constrains.
    how do we know the value of I7?
    i need it in order to calculate I5, becuase I5=I7+I1
    Thanks.

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  2. #2
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    Re: folded cascode with gm/id

    M1 is half of the diff.pair, so its current is half of the tail current. Thus M3,M4 have a 80uA current. You have to know the ratio of M11/M4 ratio to know how much is the current of M11, which equals with M7's current.
    The article states that M7 and M11's current was set by calculating the output resistance, which is not clear how was derived. The article says Lambda is computed with simulation, and probably it was used to calculate how much current is required to reach the desired total output resistance of the first stage. Sounds overcomplicated, especially if simulation was available to determine Lambda. Easier to plot operating point parameters and/or simulate output resistance directly with sweep of sizes, ratios.
    "Try SCE to AUX." /John Aaron/


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