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TINA/Spice/OPA209: OPA209

Part Number: OPA209
Other Parts Discussed in Thread: TINA-TI, , LMP7701, TLC277, TLC272

Tool/software: TINA-TI or Spice Models

I build a schmitt trigger circuit to transform sine wave to square wave. But I couldn't achieve to remove offset from output of OPA209. The circuit is on follow. What should I do remove offset ?

  • See below and attached file for recommended circuit.  If you do not have a mid-supply reference voltage available I can recommend an op amp buffer circuit that can generate it.


  • Dear Tim, thank you for your answer and the circuit. Actually I prefer not to use any reference voltage as far as possible.  I wonder that if there is possible way to remove offset from the circuit I added and work properly. And could you tell me the reason of offset? 

  • There is -40mV offset from the source (VG1). When I simulate the circuit with offset ( adding dc source valued 40mV), I cant get the proper results. Could you advise another solution to handle with offset and get square wave at output  ?

  • Hi Yildirim,

    the OPA290 shows an offset in your first simulation, because you violate the common mode input voltage range of OPA290. Your input voltage must stay away from the rails by more than 1.5V. The OPA290 is no RRIO-OPAmp.

    You should tell us more details about your voltage source. What is the source resistance? What is the signal level? And how is it connected to the signal ground of comparator?

  • There is a gaussmeter system. It generates sine wave signal. There is a -40mV offset of output of gaussmeter A1 and A2 signal. The signal is 10mV and 0.2Hz AC signal. My aim is to turn the sine wave signal to square wave signal. But offset of output of gaussmeter cannot allow to generate square wave by using comparator or zero cross detector. I try to build schmitt trigger circuit but result is same. How can I remove offset to get square wave ? COuld you offer a circuit to achieve that and remove offset ?

  • Hi Yildirim,

    if the offset voltage is constant then this circuit could do what you want:


  • Kai thank you for your answer. I tried the circuit but it does not work properly under 250mV input sine signal. Under 50mV for input signal, The output forms as sine signal and under 250mV input signal, the form of square wave corrupts. Input signal is 10mV 0.2 Hz sine signal with 40mV offset.
  • Hi Yildirim,

    here's the file:


    I have put the -40mV offset already into the voltage source.


  • Thank you for your solution. Could you suggest any TI IC to achieve that for quick solution ? or any alternative? Because I cannot find  LMP7701 in local area.

  • Hi Yildirim,

    in order to achieve a symmetrical output signal I have taken a OPAmp with a low offset voltage. And in order to achieve a full output swing I have taken a OPAmp with output rail to rail ability.

    For experimenting you can use the TLC277 or even TLC272. To achieve symmetrical output signal the TLC272 should be selected for minimum offset voltage. Or you can adjust the -40mV reference voltage.

    By the way, you can shift the output signal to any desired logic level by the use of a simple transistor inverting stage.


  • Yildirim

    We haven't heard back from you so we assume this answered your question. If not, post another reply below, or create a new thread if this one has timed-out.