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AD633 Control voltage polarity

Question asked by Gordon on Aug 30, 2012
Latest reply on Sep 5, 2012 by Gordon
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Hi Hopefully this is an appropriate place for the following question. Apologies if not.

 

     I hope someone can help me find a smarter way to resolve a small problem. I've been using the AD633 as a voltage controlled low pass filter. The problem is that the control voltage works the wrong way round for my purpose, the crossover frequency goes up as the voltage increases. I want the frequency to go down as the voltage increases. There is a way round by inverting and offsetting the control voltage but there's the potential for the control voltage to go below zero. Again there's a way round this by using a single supply rail to rail op amp with a false ground but it's all getting rather complicated.

 

Any clever way to make the AD633 work the other way round, or use something else?

 

Any suggestions much appreciated.

 

Gordon

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