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Author Topic: building a digitally controlled variable capacitor  (Read 675 times)
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the digitally controlled variable capacitor  I was looking at getting is still listed on digikey, but is no longer manufactured. so, looking at the data sheet, it looks simple to build. the question i have, is what is the control circuit called? it has something to do with a single in controlling transistors that connect/disconnect about 5 capacitors. It is a simple circuit, and seems that there should be lots of option already designed and tested.
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Got a link to what you are referring to?
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http://www.intersil.com/content/dam/Intersil/documents/fn81/fn8156.pdf
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Looks like plenty available at Mouser
http://www.mouser.com/Search/Refine.aspx?Keyword=x90100
"New At Mouser" hardly seems to indicate discontinued.
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thank you. if i can get it, then it will be the easy way and i was looking forward to building a bulky circuit.
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7.5 - 14.5 pF

How about "Fun WIth Varactor Diodes"?
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The bulky circuit you were looking forwards to building would have had far more stray capacitance than the 7.5pF to 14.5pF of the actual device.
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Perhaps you should remind us of what it is you propose to do with this digitally controlled variable capacitor.

If it is in regard to controlling the frequency of an oscillator as you have previously implied, then it is almost certainly an inappropriate approach as direct digital synthesis (of sinewaves, no less) is much more effectively and reliably performed, for which ICs are readily available.
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for which ICs are readily available.


have a little issue finding them.
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Hmmm.  How about an AD59030?
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This can be done with a 4066 quad analog switch and some capacitors
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