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  1. #1
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    To find the source resistance of the signal generator

    Can I use the following to find out the internal source resistance of the signal generator?

    I use a DC voltage source driving the signal generantor and 10K ohm resistor in series.

    Base on the current and voltage drop across the 10K ohm then I can find out how much the source resistance of the signal generator.

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  2. #2
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    Re: To find the source resistance of the signal generator

    The loop is a bit misdrawn, and the scheme would require
    you to know the generator's internal voltage amplitude
    or the 10K resistor's current (which is not shown to be
    measured, nor the added series resistance of doing that).

    If your signal generator is the normal 50 ohms then what
    you measure at the 10Kohm resistor owes more to the
    resistor tolerance than the generator impedance. A "10K"
    1% resistor could be 9900 to 10100 ohms; an ideal 10000
    ohm resistor would make the total loop resistance 10050.

    You'd need to know the "10K" resistor's value to much
    better accuracy. Or, use a test load that is closer to your
    best guess for Zout so the tolerance matters less (or not
    at all).

    Using two different resistor values is better. Like open
    circuit amplitude, and loaded amplitude, do the math.
    Presuming your signal generator isn't the kind that blows
    its output driver up when you drive it into an open load....



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  3. #3
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    Re: To find the source resistance of the signal generator

    Quote Originally Posted by dick_freebird View Post
    The loop is a bit misdrawn, and the scheme would require
    you to know the generator's internal voltage amplitude
    or the 10K resistor's current (which is not shown to be
    measured, nor the added series resistance of doing that).

    If your signal generator is the normal 50 ohms then what
    you measure at the 10Kohm resistor owes more to the
    resistor tolerance than the generator impedance. A "10K"
    1% resistor could be 9900 to 10100 ohms; an ideal 10000
    ohm resistor would make the total loop resistance 10050.

    You'd need to know the "10K" resistor's value to much
    better accuracy. Or, use a test load that is closer to your
    best guess for Zout so the tolerance matters less (or not
    at all).

    Using two different resistor values is better. Like open
    circuit amplitude, and loaded amplitude, do the math.
    Presuming your signal generator isn't the kind that blows
    its output driver up when you drive it into an open load....
    Instead of 10k ohm, what value I should use for better result?



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  4. #4
    Advanced Member level 5
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    Re: To find the source resistance of the signal generator

    Since most sign gens are meant for 50 ohms,
    I'd use something in that range. For example
    a ~40 ohm resistor and a ~60 ohm resistor
    and solve the two equations for Rout.



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