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    Why S22 curve is like this

    Hi, I am working on a triple stack amplifier. I just baised it, all transistors are in saturation, and wanted to check S22. The resistances are negative. What could be wrong. I am not sure If I can share the netlist outside for this technology. Also Is there any particular method (Like defined formulas) to provide how much bias voltage at the input of all the three transistors (Say M1 is the bottom transistor to which I give signal. Bottom M1 -> M2-> M3 (Top)) such that all of them will be in saturation. I know how to choose the gate voltage at M1 but I am not exactly sure how much gate voltage tp be given to M1 and M2. Thanks

    Anyone know any other good book for stacked transistor amplifier other than Millimeter-Wave Power Amplifiers by Jaco du Preez, Saurabh Sinha


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    Last edited by circuitking; 20th July 2019 at 17:21.

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    Re: Why S22 curve is like this

    Quote Originally Posted by circuitslave View Post
    Hi, I am working on a triple stack amplifier.
    I just baised it, all transistors are in saturation,
    and wanted to check S22.
    The resistances are negative.
    What could be wrong.
    Not wrong at all.
    Simply due to Y12.

    Calculate Yout by hand from your small signal model of MOSFET.
    https://www.edaboard.com/showthread.php?385490#3



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    Re: Why S22 curve is like this

    I want to have positive resistances. I am wondering how to make it possible



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    Re: Why S22 curve is like this

    You amplifier may be unstable..



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    Re: Why S22 curve is like this

    Quote Originally Posted by BigBoss View Post
    You amplifier may be unstable..
    Yes it is, but If I have to keep degenerative inductor it needs to a huge value. I tried with small inductance values but still it is unstable.



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    Re: Why S22 curve is like this

    Quote Originally Posted by circuitking View Post
    Yes it is, but If I have to keep degenerative inductor it needs to a huge value. I tried with small inductance values but still it is unstable.
    There are methods to stabilize an amplifier such as connecting a resistor at input and/or at output.A negative feedback may also stabilize the amplifier..



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    Re: Why S22 curve is like this

    Quote Originally Posted by circuitslave View Post
    I want to have positive resistances.
    I am wondering how to make it possible
    Surely learn and understand following.
    https://www.edaboard.com/showthread.php?384656#4



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    Re: Why S22 curve is like this

    Quote Originally Posted by BigBoss View Post
    There are methods to stabilize an amplifier such as connecting a resistor at input and/or at output.A negative feedback may also stabilize the amplifier..
    I have seen in a book, a capactior is also used. I am still wondering how bias is provided when capacitor is kept in the signal path as shown in the figure.

    Click image for larger version. 

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  9. #9
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    Re: Why S22 curve is like this

    Quote Originally Posted by circuitslave View Post
    I am still wondering how bias is provided
    when capacitor is kept in the signal path as shown in the figure.
    Simply bias circuitries are not showed.
    That’s all.



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    Re: Why S22 curve is like this

    Quote Originally Posted by pancho_hideboo View Post
    Simply bias circuitries are not showed.
    That’s all.
    I know that bias is not shown. If at all bias is connected, where should it be connected?.

    Anyway, I found out where It should be connected without disturbing biasing.



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