voltage feedback operational amplifier with rail-to-rail output

Discussion in 'General Electronics Chat' started by gigilala, Sep 29, 2006.

  1. gigilala

    Thread Starter New Member

    Sep 29, 2006
    1
    0
    Hi,

    I do not understand what does rail-to-rail output mean.

    Why and when do we need to use a voltage feedback operational amplifier with rail-to-rail output?

    Hope to hear from you all soon.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    An op amp with a rail-to-rail output can slew its output vo;tage to equal the value of the supply rails. Normally, there is a diode drop or two in circuit, and an op amp's output voltage can only get to within a large fraction of a volt to the supply rail.

    If your signal is a couple of volts and the supplies are +/-12 volts, this is not a big deal. However, if your supplies are +/-3 volts and your signal needs to be +/- 2.9 volts, having a rail-to-rail capability is quite significant.
     
  3. gigilala

    Thread Starter New Member

    Sep 29, 2006
    1
    0
    Thank you for your reply.

    Does it mean that the output voltage can go up to +/-11.9V if the supplies are +/-12V for this type of op amp rather than just +/- 11V for the other types?

    I am doing an ECG circuit recently. I need to take into consideration of the baseline wander which will containminate my ecg signal when there is any body movement. It will shift up my ecg signals that is centered at the X-axis initially and this can result in saturation of the amplifier.

    Can I use the feedback rail-to-rail op amp to deal with this problem? If yes, then how to do? Please help......
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Getting an op amp with a couple of more volts output swing is not the best way to solve your circuit problems. I have no idea of what your ECG setup is built like, but your baseline shift makes me think your reference electrode is not doing its job.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Getting an op amp with a couple of more volts output swing is not the best way to solve your circuit problems. I have no idea of what your ECG setup is built like, but your baseline shift makes me think your reference electrode is not doing its job.
     
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