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Problem with AD633 Square Rooting

Question asked by Benoit on Sep 17, 2015
Latest reply on Oct 23, 2015 by Benoit

Hi everybody,

 

I have a problem with the AD633AZR: I have a 2V offset in the output, which is intolerable for my application (active anti-noise system).

 

I have build my circuit with the Figure 15 Page 9 of the datasheet Rev. K.

Here is the datasheet (Rev.K) :http://www.analog.com/media/en/technical-documentation/data-sheets/AD633.pdf

 

Well, you can see attached how I have connected my circuit.

 

While I have a negative redressed sinus entrance (Ve), W, which should be exactly the opposite, has an offset evolving with the frequency. Then, the square output has a more or less 2V offset (Vs).

 

I tried to put the diode D2 (only avoid an oscillation).

I tried to pu the Optional Offset Trim Configuration (Figure 11 Page 8) which didn't helped.

I have put the 10nF capacitor between the output of the AOP and X1/Y1 but an oscillation appears more quickly.

 

I have this values:

 

 

f (Hz)VeminWmaxWmin
500

-3V

-6V
-7,5V

less we have an ascillation on W

-3V

-6V

-7,5V

200mV

310mV

400mV

1000

-3V

-6V
-7,5V

less we have an ascillation on W

-3V

-6V

-7,5V

310mV

520mV

600mV

2000

-3V

-6V
-7,5V

less we have an ascillation on W

-3V

-6V

-7,5V

500mV

800mV

1V

 

How can I deal with this offset? How could I delete it? I need to have very accurate signals...

 

Thanks a lot for your help.

 

Please tell me if you need any information.

 

Best regards.

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