Proteus problem in wave generation

Discussion in 'General Electronics Chat' started by Sherko, Mar 15, 2015.

  1. Sherko

    Thread Starter New Member

    Feb 18, 2015
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    HI,I have a circuit that generate a sine wave based on hartley oscillator but i added an OP_AMP ic to circuit screen board in proteus that is not connected to any thing but when exists in board outpu of oscilloscope is nothing but when i delete OP_AMP from screen everything works good and oscilloscope shows generated sine wave ehat is problem?why this occur?is this a proteus problem or i can handle this problem?
    it gives this error : [SPICE]Gmin step[110 of 120] failed:GMIN =5.62341e-012
    what this error means?
    here is my circut:
    http://forum.allaboutcircuits.com/a...8/?temp_hash=a797cf4f0b72d0e7412a185c88bd38f6
     
    Last edited: Mar 15, 2015
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I cannot see your attachment, so cannot comment on your usage of the opamp.

    The GMin stepping error in Spice is usually caused by a highly non-linear circuit in combination with inductance and capacitance, or possibly a badly-written device model.

    Show me your circuit and I will try to run it in LTSpice, which has a highly-tuned Spice calculation engine to minimize this type of error...
     
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  3. Sherko

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    Feb 18, 2015
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  4. MikeML

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    That oscillator appears to run somewhere near 200Khz. Running even a fast opamp open-loop as a comparator (with no feedback) is not the best way to do this. A high speed comparator chip would be better.
     
  5. Sherko

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    Feb 18, 2015
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    how i can fix it ,i need more details to understand?what is feedback?
     
  6. MikeML

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    In your circuit, the opamp is used not as an amplifier, but as a comparator, meaning its output pin slews from the most positive output to the most negative output and back again in order to square the output wave. OpAmps are not designed to do this. If over-driven (as yours is), the output stage of the opamp is forced into an un-natural state, where transistors inside the opamp are overdriven. An overdriven opamp comes out of that state slowly, slowing the rise and fall times of the desired square wave.

    A high-speed comparator, such as these, is specifically designed for this task.
     
  7. Sherko

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    Feb 18, 2015
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    hi,i replace op-amp ic with a high speed comparator ad8001 but still no wave generation?
     
  8. MikeML

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    You are missing a DC path for the input bias current of the comparator.

    Move R6 (10K) from where it is now to between the non-inverting input of the comparator and the tap between R1 and R5 (0.1Vcc). C8 stays.\

    AD8001a is not a comparator; it is a special opamp. Whenever you want to use an ic in a circuit, always read the manufacture's data sheet
     
  9. Sherko

    Thread Starter New Member

    Feb 18, 2015
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    can i ask you to complete this circuit to convert generated sine wave to a square wave in a way it is possible and give me a picture of your circuit i did anything that i could with this circuit to do that but no succeed?
     
  10. MikeML

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    Do you need both the sine wave and square wave at the same time?
    What amplitude should the square wave be?
    What frequency should the oscillator actually run at?
    Must you use a Hartley?
    What about a Colpitts (doesn't require a tapped inductor)?
    What supply voltage do you want?

    For example:

    176a.jpg
     
    Last edited: Mar 16, 2015
  11. Sherko

    Thread Starter New Member

    Feb 18, 2015
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    yes i need both wave's in 200khz
    the amplitude of square wave is not important ,
    yes i want hartley oscillator
    12v supply voltage
     
  12. absf

    Senior Member

    Dec 29, 2010
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    In proteus you need a single pulse to kick start the oscillator like this....

    SIN2SQR_1.PNG

    Allen
     
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  13. Sherko

    Thread Starter New Member

    Feb 18, 2015
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    thank you brother so much you helped me so much .god bless you
     
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