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OPA810: OPA810 Output Distortion

Omer YILDIRIM
Prodigy 40 points
Part Number: OPA810
Other Parts Discussed in Thread: OPA2197

I bought OPA810 from Digikey. I ran into such a problem while doing the tests. When I compared the input and output in the voltage follower circuit, I observed that there was distortion in the output. When I tried it with another OPA810, I got the same result. I feed the OPA810 with -5V and +5V. Do you think there is a problem with OPA810?

  • 0
    Prodigy 40 points

    Also, when I apply 0V to the input in the voltage follower circuit, the output is around 400mV. It is stated in the datasheet that the input offset voltage is 100uV. I guess there is a problem there too. I got the same result on both OPA810s I tried.

  • 0 in reply to Omer YILDIRIM
    TI__Intellectual 1580 points

    Hi Omer,

    This behavious is not expected.

    We also tested the device OPA810 with the same test condition in our lab but didn't see any issue (See the waveform plot below).

    Are you testing the device in PCB with proper board layout or in a breadboard/veroboard type setup.

    Can you please share the schematic and PCB picture also.

    Regards

    Anant Sinha

  • 0 in reply to Anant Sinha
    Prodigy 40 points

    Hi Anant,

    I am testing the device in breadboard using SOP8 to DIP8 adapter. I am using Analog Discovery 2 as a signal generator and oscilloscope. When I test with OPA2197 in the same setup, I get the same results as yours. However, I'm having problems with my tests with the OPA810 on the same setup.

  • 0 in reply to Omer YILDIRIM
    Prodigy 40 points

    Hi Anant,

       

    This is OPA2197's test setup and result.

  • 0 in reply to Omer YILDIRIM
    TI__Intellectual 1580 points

    Omer,

    OPA810 is high speed amplifier and it has a much higher GBP of 70Mhz as compared to OPA2197 which has GBP of only10Mhz.

    For any high speed amplifer it is not advisable to test the device in a socket and breadboard type setup. The parasitics from such setup will negatively impact the device's performance and can even make it unstable. You need PCB with proper layout, component placement and supply decoupling capacitors to get the best performance out of the device. You can refer to section 11 of the OPA810 datasheet for more detail on this.

    Regards

    Anant

  • 0 in reply to Anant Sinha
    Prodigy 40 points

    Hi Anant,

    Well, when I give a constant 0V to the input of the voltage follower circuit, is it related to the experimental setup that I get 400mV from the output? And I got this result in my experiments with two different OPA810s. Is it normal to have such an effect even though I work with DC voltage?

  • 0 in reply to Omer YILDIRIM
    TI__Intellectual 1580 points

    Hi Omer,

    Most probably you device is not stable in this setup and has some high frequency oscillation. The Analog Discovery 2 oscilloscope has bandwidth of only a few MHz when used without BNC adapter ( even when used with BNC adaptor and coax cable the max -3db BW is only 30MHz). So any oscillation above the BW of the scope will be filtered out or attenuated (based on freq) and you will only see it's DC value. So the shift in output which you are seeing (in both case when forcing 0V or when giving triangular input) is probably because the average value of the oscillation signal is 400mV.

    One thing you can try is putting suppy decoupling capacitor on both Vcc and Vee. It might help in improving the performance.

    Also, if you have access of any Higher Bandwidth Oscilloscope and probe (BW>200Mhz) try probing the output with that and you should be able to see the device oscillating.

    Regards

    Anant

  • 0 in reply to Anant Sinha
    Prodigy 40 points

    Hello Anant,

    As you said, when I reduced the time division, I saw that the device oscillates around 48MHz. Not much reduction with decoupling capacitors. Do you think this problem can be solved with PCB? Will I have the same problem as I had on the breadboard?

    Thanks.

  • +1 in reply to Omer YILDIRIM
    TI__Intellectual 1580 points

    Omer,

    Yes definitely, it should get solved with PCB but make sure to follow proper guideline for layout. Refer to Section 11 of the OPA810 datasheet for more details on this.

    Regards

    Anant