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Re: [Electronics_101] when does an opamp get saturated

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  • Howard Hansen
    From your description it appears you are at a college and will have access to a signal generator and oscilloscope. There are two tests you can easily run to
    Message 1 of 3 , Jul 2, 2010
      From your description it appears you are at a college and will have
      access to a signal generator and oscilloscope. There are two tests you
      can easily run to check for saturation. One first set the opamp's gain
      to 100, connect the signal generator's output to the opamp's input and
      the signal generator's output level to 4mv peak to peak . Connect the
      oscilloscope to the opamp's output. Now if the opamp is not saturating
      the signal displayed on the oscilloscope will be an amplified version of
      the input signal. If the output signal is a distorted version of the
      input signal than the amplifier is saturating. Next repeat this step for
      input signal levels of 8, 10, 20, 40, 80, 100, 200 and 400 millivolts
      peak to peak. At one of these input signal levels you will start to see
      distortion in the output signal. When you start to see distortion do not
      increase the input signal amplitude any further.

      The next test is to run a test similar to the above but instead of
      varying the input voltage vary the opamp's gain. Initially start with an
      opamp gain of 10 and an input signal level of 4mv peak to peak. Then
      increase the opamp's gain to either 20, 40, 80, 100, 200, 400, 1000 or
      until the opamp's output signal is no longer an amplified version of the
      input signal.

      Howard

      kishan raithatha wrote:
      >
      > hello,
      > when does an opamp get saturated or what is saturation in an amplifier?
      > I have built an instrumentation amplifier circuit and a right leg drive
      > circuit.The instrumentation amplifier used is ad620 which has a
      > programmable
      > gain .i m attaching the pindiagram of ad620 and the circuit that i
      > have made . i
      > m building initial amplifier circuit for capturing cardiac signals.i
      > have taken
      > the signals from hands by using the clamp electrodes.i m getting the
      > cardiac
      > signals but those are in the range of 90mv even after amplification.i
      > have set
      > the gain to 1000 of ad620.So normal cardiac signal when measured from
      > hands
      > without amplification are in the range of 4mv so after amplification i
      > should
      > get atleast 1 V output which is my requirement so that i can further
      > process the
      > signal.When consulted with one of our professors he said that as you
      > are keeping
      > the gain so high the opamp would be getting saturated and wont be able
      > to get
      > the desired signal strength.so i want to know what is saturation in
      > amplifier
      > and if anyone can point if something is wrong in my circuit.
      >
      > kishan
      > attached :
      > 1):pin diagram of ad620
      > 2)instrumentation amp and right leg drive circuit
      >
      > [Non-text portions of this message have been removed]
      >
      >
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