LTspice simulation with inverting op amp

Discussion in 'Homework Help' started by coolrox86, Oct 13, 2011.

  1. coolrox86

    Thread Starter New Member

    Oct 13, 2011
    6
    0
    Hello, I'm new here.

    I'm currently using LTspice software to simulate a circuit of inverting operational amplifier, to amplify the sine wave input voltage from amplitude 1V to output 5V. However the simulation never display the desired result.

    I have attached my ltspice file below for reference. I really appreciate for those who are willing to provide useful tips and help. Thanks!:)
     
    • plan.asc
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    Last edited: Oct 13, 2011
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Your simulation has a few problems.
    1) The opamp is not an ideal opamp; the LT1006 model you used is a very good one, but it does require connections to a voltage supply. Also, since your input is a true AC voltage, you will either need to use a dual supply (± 10v for example) or you will need to offset the input from ground. You should never let the input to an opamp or comparator exceed the power rails (go higher than the most positive supply pin, or go lower than the most negative supply pin).

    2) You are using VERY low values for the feedback resistors. Generally, I like to stay somewhere between ~2k Ohms and ~200k Ohms or so where possible. Going lower than ~2k Ohms in the feedback path can prevent an opamp's output from swinging as wide as it ordinarily could. If you use really large values of resistance, you will make a real circuit much more susceptible to noise.

    So, instead of 0.1 and 0.5 Ohms, try 20k and 100k Ohms. Those are both standard values of resistance, and should work just fine for your purpose.

    Hint: Use the "Label Net" feature (looks like a sign with an "A" in it) - you can label nodes like the output of the opamp with "Out", the opamp inputs with "+" and "-" - it makes it much easier to compare the plot outputs to the schematic than the default node names like "N002", etc
     
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