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TL084: no phase reversal

Amy Luo
Expert 6895 points
Part Number: TL084


Hi team,

As explicitly stated on datasheet, this chip is no phase reversal, as shown below:

But one of our customers actually tested the waveform like this:

Test conditions：supply ±10V, input sinusoidal Vpp 20V, frequency 10kHz, test circuit shown

I don't have circuit boards here to actually verify, where do you have a chance to verify this feature, or are there any problems with the way the customer tests it?

In addition, I have emulated this circuit with TINA and the output is normal

Thank you,

Amy

  • +1
    Guru 140200 points

    Hi Amy,

    I knew that this would happen one fine day...

    The absense of phase reversal is only valid for the new TL084H but not for the old TL084 Frowning2

    Kai

  • +1
    TI__Guru**** 167786 points

    Hello Amy,

    Kai is correct that only the TL084H section of the curves states 'no phase reversal'. However the other versions do not make that claim. The classic TL084 will fully phase invert as you have seen. 

    A correction still needs to be made because TL084H will phase invert to a lesser extent. When the input common mode is too close to the V- supply, the device can invert. In your example circuit, when input becomes too low the input stage will cutoff. In cutoff, the output may go high or low. If output wants to go low, VOL will occur.  If output wants to go high the output will start to go high, but just high enough to bring the common mode (at IN-) back into operation (not cutoff).