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I'm using a rail-to-rail op amp (LM6132) with its power rails at -5V and +5V, connected to a function generator. I expect to be able to give it a maximum signal of 10V peak-to-peak ((i.e. -5V to +5V)) without seeing much clipping, but as soon as the signal reaches about 4.9V peak-to-peak, clipping begins. Could anyone help me understand why this is?

Thanks in advance!

edit: pictures! The oscilloscope shows the measurement from the wire pointed at by the arrow, with the input signal being 5.5V peak-to-peak without the wrong label the oscilloscope measuring from the arrow, showing clipping. Input signal has peak-to-peak amplitude of 5.5V

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    \$\begingroup\$ What's the load? A schematic of exactly what you have showing decoupling caps, resistor network if any, and scope shots of Vin and Vout would be helpful. \$\endgroup\$
    – John D
    Commented Aug 24, 2017 at 18:48
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    \$\begingroup\$ What load do you have on the output? What gain configuration? What input frequency? Where's the schematic? \$\endgroup\$
    – Andy aka
    Commented Aug 24, 2017 at 18:49
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    \$\begingroup\$ I expect to be able to give it a maximum signal of 10V peak-to-peak ((i.e. -5V to +5V)) And why would you expect that ? Look at the datasheet, even with a 100 kohm load this opamp cannot bring the output exactly to the supply rails. Almost no opamp can. You will need some margin, if you want 10 Vpp then you need to supply the opamp with +/- 5.1 V or more. \$\endgroup\$
    – Bimpelrekkie
    Commented Aug 24, 2017 at 19:00
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    \$\begingroup\$ Gah... -1 for the complete waste of everyone's time. It's OK to make a mistake. This has been one mistake after the other, invalidating every answer as soon as they come in. \$\endgroup\$
    – pipe
    Commented Aug 24, 2017 at 19:49
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    \$\begingroup\$ Most function generators (all?) are by default set to show the voltage you'll get on a 50-Ohm matched load. Because they have a 50-Ohm output resistance, they output 2x what they are showing, because that will be halved under 50Ohm load. \$\endgroup\$
    – next-hack
    Commented Aug 24, 2017 at 19:49

2 Answers 2

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EDIT: The following considerations are valid only considering the old (unedited) question, which was referring to LMX321 and not LM6132. /EDIT

Looking at the datasheet https://datasheets.maximintegrated.com/en/ds/LMX321-LMX358.pdf I see that the absolute maximum value of VCC-VEE is 8V. You're giving 10. That's probably why it saturates at +/- 5.5/2 V, and it does not even go close to 10Vpp.

No smoke? :)

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  • \$\begingroup\$ Is that the same one as this? ti.com/lit/ds/symlink/lm6132.pdf I had to remove the original link due to lack of reputation points, sorry. \$\endgroup\$
    – janizer
    Commented Aug 24, 2017 at 19:14
  • \$\begingroup\$ Hmm..he had the TI part listed before ..... which has a much wider range. \$\endgroup\$
    – Trevor_G
    Commented Aug 24, 2017 at 19:15
  • \$\begingroup\$ No, because that one has, for instance, a much wider power supply range, and goes up to 24V (+/- 12) \$\endgroup\$
    – next-hack
    Commented Aug 24, 2017 at 19:16
  • \$\begingroup\$ The OP has changed the part number to LM6132, therefore my answer is no longer valid, as it refers to the original part (LMX321). \$\endgroup\$
    – next-hack
    Commented Aug 24, 2017 at 19:19
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    \$\begingroup\$ Now schematics has changed too. \$\endgroup\$
    – next-hack
    Commented Aug 24, 2017 at 19:29
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enter image description here

This is for +5V Vcc. Increase the PSU voltage for that extra milivolt you need. It has to be clear that even if the opamp is rail to rail it doesnt mean that the output swing will be the supply voltage and even linear to the last milivolt.

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    \$\begingroup\$ ALso missing the point. He is running the thing at 10V supply..not 5V. \$\endgroup\$
    – Trevor_G
    Commented Aug 24, 2017 at 19:06
  • \$\begingroup\$ @Trevor By the time I wrote an answer, the OP has changed the description almost three times. \$\endgroup\$
    – Marko Buršič
    Commented Aug 24, 2017 at 19:09
  • \$\begingroup\$ @MarkoBuršič I just added some pictures. My issue is still getting a 10V supply to have near to 10V output swing. \$\endgroup\$
    – janizer
    Commented Aug 24, 2017 at 19:10
  • \$\begingroup\$ I saw it on the firs iteration, but it is confusing with everything using basically the same number... \$\endgroup\$
    – Trevor_G
    Commented Aug 24, 2017 at 19:11

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