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OPA140: OPA140

Kuan Wei Chen (Kevin Chen)
Genius 9710 points

Part Number: OPA140

Dear Team,

We are learning from the precision lab video.

If we use (+-5V) on OPA140 as the supply voltage.

Function generator to 50kHz, 9Vpp, oV offset, 50% symmetry.

We can see distortion at around 2.0V+.

But when operate in 1kHz the distortion didn't occur(actually a small distortion).

The training material mention OPA140 is actually rail to rail at low frequencies, but how can I find it on the datasheet?

How low the frequency should it be?


Please kindly provide the information

Best regards

Kevin

  • 0
    TI__Genius 11135 points
    Kevin

    Could you send a schematic and maybe a scope photo of the distortion you're seeing?

    Thanks
    Dennis
  • 0
    TI__Guru* 93105 points
    Hello Kuan,

    I recall observing the OPA140 distortion behavior that you have noted when the large signal frequency is increased to tens-of-kilohertz, and that it isn't present at a low frequency such as 1 kHz. The distortion on the positive portion of the waveform seen at 50 kHz is due to the internal positive common-mode voltage (VCM) of (V+) - 3.5 V. Once that limit is exceeded the op amp operates in a region where the linearity suffers and other ac parameters degrade. The distortion may be considerably less at DC and low frequencies compared to high frequencies because the open-loop gain is very high at low frequencies.

    The OPA140 datasheet does not reflect this behavior, but simply states the VCM range is (V-) - 0.1 V to (V+) -3.5 V. The best plan is to stay within the specified limits if the the distortion is to be avoided.

    Regards, Thomas
    Precision Amplifiers Applications Engineering
  • 0 in reply to Thomas Kuehl
    TI__Genius 9710 points
    Dear Thomas,
    Thanks for the reply, it solve my issue.

    Dear Dennis,
    Thanks for the reply.

    Best Regards
    Kevin