AD8033 distortion

Hello.

I have a circuit with an AD8033 in voltage follower topology (gain=1), with Vs+=24V, Vs-=0V (GND).

The input signal is a positive sine of 10Vpp.

In figure 1, at frequency 100kHz, the output (blue) follows the input (yellow).

1c82f882051acdad6c43215281a77c9a.tiff

In figure 2, at freq. 2.5MHz, the output is distorted around 0V.

7c4741cf234d34acde6885e852746f2e.tiff

In figure 3, at 2.5MHz, if the low level of the input is shifted to 900mV, the output is not distorted anymore.

c07356dc4bf403322f1b2dd11a4d7cd8.tiff

Now, with Vs+=5V, Vs-=0V (GND) and an input signal of 4Vpp (positive sine) at 1MHz, the output is like in figure 4. Again, if the sine amplitude is reduce within the supply railes (say 1V to 3V), the output is not distorted anymore.

e87ceeeb6acff2a8abe692b546c6a50a.tiff

There is a post in this forum that says that the input range of the AD8033 is from Vs- (in this case 0V) to 3V below Vs+. I think this is not true because the opamp has a bipolar differential input pair that allows the input to go beyond the positive rail.

What may be causing the problem? It's not seem to me a slew rate or bandwith problem..

  • 0
    •  Analog Employees 
    on Feb 23, 2015 6:42 PM

    Hi Manu,

    Thank you for considering ADI parts for your applications. In figure 2, it looks like the distortion is due to the headroom on the output voltage swing of the part. Although it is said on the datasheet that the AD8033 have rail to rail outputs, there is no actually true rail to rail amplifiers and the output swing will always have few millivolts headroom from the supply rails. In figure 2, since you are using a single supply voltage of 24 V, you should not expect that the output can go exactly to 0 V. I would recommend to always check the datasheets and look for the output voltage swing specification as shown below:

    VS = +/- 12V

    It is also indicated on the datasheets that the input common mode voltage of the parts for 5 V single supply operation should only be limited to 0 to 2 V only as shown below:

    We should always check and  follow the conditions declared on the datasheets for us to achieve the specified performance of the parts.

    I hope this helps.

    Best regards,

    Emman