How to add negative bias

Discussion in 'The Projects Forum' started by SAnton, Oct 23, 2008.

  1. SAnton

    Thread Starter New Member

    Oct 19, 2008
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    Hello! I have square-wave signal from the generator, but it is unipolar, i.e. GND to +15V. In my application I need some negative DC bias, but there is one and the main problem - fast pulse response needed with 50-100 nanoseconds rise and fall times, so this circuit must be at least high-speed. See the attachment. Thanks...
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Why not capacitively couple it, so it goes both ways. You could bring the negitive side to whatever voltage using diodes.
     
  3. SAnton

    Thread Starter New Member

    Oct 19, 2008
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    Could you draw schematics of it?
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    Greetings Santon,

    Here is a link to the section in AAC ebook on diode clamping. The technique Bill mentioned is referred to as dc-restoration. It involves introducing a capacitor into the signal line to block the existing DC component of the signal and then using a diode and a voltage reference to establish the new DC component needed.

    hgmjr
     
  5. SAnton

    Thread Starter New Member

    Oct 19, 2008
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    0
    Thanks for good info!
    As I understood, capacitor coupling is suitable for sine wave signals, but what will be with the square-wave signal?
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    The low freq parts are attenuated more than the high freq parts. If the cap is big enough, you can't tell the difference, otherwise the edges get through pretty cleanly.
     
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