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200 MHz Triangular Wave

Discussion in 'Homework Help' started by Ng Jing Xi, Oct 22, 2013.

  1. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I made a mistake yesterday with my level shifter.
    The inputs must be swapped so that the reference voltage must be +3.75V on the (+) input of the opamp.
    For the output to swing as high as +15V then the positive supply must be at least +17V so use +18V.
    For the output to swing down to 0V then the negative supply must be -2V or more negative so use the existing -12V.
    The output will be a level shifted input but it will be inverted.

    The TL072 and almost every other opamp has difficulty driving a negative feedback resistor value as low as 1k so I used 10k.
     

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  2. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    You would probably be better off applying the signal to the inverting input resistor and applying half the required offset to the non inverting terminal. If you apply the signal to the non inverting terminal you get a gain of 2 which you probably dont want.

    Keep in mind that the offset plus the peak can not go over the max output that you can get from the op amp you are using and it's power supply level. So if you have a plus and minus 5v input for example with a 1v offset voltage applied to the non inverting terminal, you'll get a triangle that goes from -3v to +7v. If you apply only a 0.5v offset then you'll see it go from -4 to +6v at the output.

    If you really need to apply a voltage that must be equal to the actual offset, then use a differential amplifier connection. That way when you apply 1v you'll actually get a true 1v offset not a 2v offset.
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    In my last post my corrected circuit is similar to the one described by MrAl.
     
  4. dave

    Dave New Member

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  5. Ng Jing Xi

    Ng Jing Xi Member

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    Thanks Audioguru and MrAl, I understood what you guys meant. Thanks so much
     

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