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AD8033 distortion

Question asked by photoniczen on Feb 23, 2015
Latest reply on Feb 23, 2015 by Emman.A

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).

TEK00094.TIF

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

TEK00097.TIF

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

TEK00100.TIF

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.

TEK00103.TIF

 

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..

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