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Need help in deriving equation 7, 8 and 9 in Input Impedance Matching With Fully Differential Amplifiers by James Karki

Hi

The article in question is: www.ti.com/.../slyt310.pdf

I am going through the derivation of how to calculate the input impedance and the gain of differential amp with single input ( not differential input) for my design. I cannot verify formula 7, 8 and 9. I read all the articles provided by Ti that are written by James Karki already. I understand the formulas from SLAO54E and "Analysis of fully differential amplifiers" by James Karki, but I just cannot jump the gap from all these to formula 7, 8 and 9.

It would be nice if I can write directly to Jame Karki if it is all possible.

Thanks

Alan

  • Hello Alan,

    Here is a spreadsheet that will help with your equations.  This spreadsheet is very useful to help select resistor values and is very convenient especially when  you need a particular input impedance and gain. 

    Regards,

    Loren

    8272.FDA single to diff resistor calculations with BW and Noise calculations to share.xlsx

      Every day you are alive is another opportunity to make the world a better place. 

  • In reply to Loren Siebert 1:

    Hi Loren

    Thanks for the spreadsheet. But what I am asking is how to derive the formula, not the calculation or simulation of the resistor value. I am working through the formulas to verify equations 7, 8 and 9.

    Thanks

    Alan

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