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Voltage offset

Discussion in 'Electronic Design' started by [email protected], Mar 6, 2008.

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  1. Guest

    I want to read a voltage on a ADC that only accept 0-5V. My input
    signal is 12Vp-p (-6 to 6). I simulate this circuit and it work. I
    have 0 to 4.45V on Vout. My question is, do this circuit can easely
    induce noise in my VCC. Or this only depend on how I will layout my
    component on the PCB? Using a op-amp in differential is more safe than
    this? My signal is 20 KHz.


    (Use courrier new)

    R1 - 1.2K
    -----------/\/\/\/\----------------o Vout (go to ADC)
    | |
    | |
    | |
    | \
    ------ /
    |sin(x)| \ R2 - 1K
    ------ /
    | \
    | /
    | |
    | |
    | |
    | ------- 5V
    | ---
    | |
    | |
    |-----------------------------
     
  2. Guest

    Pardon me, but I don't understand the term "rail", do you mean my
    power supply source? If so, yes my 5V *reference* is directly from my
    main power
    supply source.

    From the thow reply a see, once said it's ok and you said I can be in
    trouble!!!
    What's the real story?

    I have design a circuit using a op-amp to obtain the same result, but
    op-amp is *expensive* compare
    to the above circuit, but if a running after trouble with this design,
    I will go for an op-amp.
     
  3. Mook Johnson

    Mook Johnson Guest


    I would highly suggest doing the attenuation/level shift using a good, high
    bandwidth opamp to drive the ADC input. The ADC sucks a narrow, high peak
    current when it samples and a 500ohm source impedance will surely wiggle in
    this condition. A good high bandwidth opamp (say an AD8031) would make a
    good buffer for the ADC input. Running the opamp off 0-5V will also protect
    the ADC from damage if your sine input signal gets zapped or goes higher
    than the expected voltage.
     
  4. Fred Bloggs

    Fred Bloggs Guest

    This is about the same as your circuit but greatly attenuates the 5V
    noise to be expected in a digital system...
    View in a fixed-width font such
    as Courier.
     
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