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TL064: Output voltage > Input voltage on voltage follower

Part Number: TL064
Other Parts Discussed in Thread: TINA-TI, TL072

Hi,

The symptom that input signal is gained in spite of the voltage follower occurs as below attached.

This situation occurs on the below situation;

V+=5.231V, V-=-4.959V, Input signal= 3.8V(DC)+150mVpp, f=16Hz.

When the input DC voltage gets down, the Input signal isn't gained.

This symptom doesn't depends on input signal frequency.

What is the cause of this symptom?

Best Regards,

Kuramochi

  • Hi Kuramochi,

    When you say the signal isn't gained, what do you mean? In a buffer configuration, there should be no gain on the output. What is the output voltage of the amplifier in this condition - can you attach measurements?

    I suspect that you are likely running into an output swing limitation on the amplifier, as your DC level is only 1.4V from the positive supply rail.

    Best,
    Paul
  • Kuramochi-san,

    Paul is correct. This voltage is close to the maxim VOH of the TL064. The output should be clipping the top of the 16 Hz waveform. Therefore the gain should be less than 1 not greater than 1.

    If this is not the case, waveforms will be helpful.
  • Hi Kuramochi,

    your numbers make no sense to me. Can you post a schematic of your circuit? You could draw it Tina-TI.

    Is your input signal +3.8VDC or -3.8VDC? What is the gain of your TL064 circuit? Is it a unity-gain follower with gain = 1?

    Kai
  • Everyone,

    Thank you for your comments.

    I forgot to attach the file.

    Could you check the below file?

    TL064 waveform.xlsx

    Best Regards,

    Kuramochi

  • Hi Kuramochi,

    please have a look into the datasheet of TL064. In 6.3 you will find the recommended operation conditions. Please note, that you must stay away from the supply rails by more than 4V. So, with a +/-5V supply your input voltage (DC plus AC components) must not be higher than +1V and not lower than -1V. With 3.8VDC +150mVpp you heavily violate this recommendation.

    Please keep in mind, that the TL064 is no input output rail to rail operational amplifier.

    Kai

  • Kuramochi-san,

    The only time the gain would increase is having the input voltage was too close to the negative supply voltage. Are you very sure the DC component of the input signal is +3.8V? Please measure it again.

    See section 8.3 "unity gain buffer" in the TL072 data sheet.
    www.ti.com/.../TL072

    Figure 28 shows a gain up to 1.4 near the lower end of the input common mode. The gain drops abruptly to 0 on the upper end due to output high drive limitation. TL072 is not exactly same as TL064, however they are similar.