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low level sine wave generator

Discussion in 'General Electronics Discussion' started by peterluke, Oct 11, 2013.

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  1. peterluke

    peterluke

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    Oct 10, 2013
    Hi Folks:

    I need a 100uV p-p 10 to 20 Hz sinewave signal to test a set of EEG amplifiers since my Wavetek signal generator don't produce this kind of signal so I've to built one myself, the sine wave generator part is not too hard but I have trouble figuring out how to get a uV level differential output from a sinewave generator circuit, the whole circuit is powered by a 9v battery, any help is appreciated.

    Cheers!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If you can get a 1V p-p signal then you can use a voltage divider to get a 100uV peak to peak signal.

    100uV / 1V = 100/1000000 = 1/10000.

    So a voltage divider made up of a 9999 ohm resistor and a 1 ohm resistor will give you 100uV p-p across the 1 ohm resistor if 1V p-p is placed across both resistors.

    In practice you could use 10k and 1 ohm, since the difference between 10k and 9.999k is far less that the expected variation in resistor values given their tolerance.

    Naturally also, if your output is something other than 1V p-p then you need to recalculate the resistances required.
     
  3. peterluke

    peterluke

    4
    0
    Oct 10, 2013
    Hi Steve:

    Thanks for your help, that would work, the EEG amp input is an instrument amp with differential input, so how do I convert the output of the resistor network into a differential output ?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,270
    2,718
    Jan 21, 2010
    You would take the signal from either side of the 1 ohm resistor.

    However if you want the signal to be symmetrical around some other level then you would need to ensure that your signal generator is floating with respect to that level and connect your ground to the centre of another voltage divider across the 100uV output (It could be a pair of 1k resistors).

    At low frequencies like this, it should be fine.
     
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