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I'm working on my project during this i face some problems... Here i mention my problem:-

  1. I required some variable capacitance whose range is C=0.05pF to C=0.5pF. So there is any variable capacitance available.so please send me the name as soon as possible.

2.It is possible to connect two varactor diode in series.and if it is possible so what is the effect of parasitic capacitance

Please send me the solution as soon as possible..

Thanks!!!

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  • \$\begingroup\$ I am just curious, why do you need such low capacitances? \$\endgroup\$ – Golaž Apr 22 '15 at 13:00
  • \$\begingroup\$ It is related to my project( phase shifer for antenna).so please tell me there is any variable capacitance for this range?? \$\endgroup\$ – ravi Apr 22 '15 at 13:08
  • \$\begingroup\$ I doubt you'll find trimmers with such low capacitances. Maybe some custom made? Can't you change any other components in your circuit to allow for bigger capacitances? \$\endgroup\$ – Golaž Apr 22 '15 at 13:10
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    \$\begingroup\$ If you are tuning an antenna you can use a higher capacitance varactor diode in parallel with an inductor. At perfect resonance the parallel combination has very high impedance and does not produce any tuning. As varactor voltage is lowered this detunes the tuned circuit slightly lower producing a net capacitive effect. \$\endgroup\$ – Andy aka Apr 22 '15 at 13:25
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    \$\begingroup\$ @SpehroPefhany dunno - it just sprang to mind \$\endgroup\$ – Andy aka Apr 22 '15 at 13:52
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Yes, you can get into this range using GaAs microwave varactors. They tend to come in inconvenient packages such as flip-chip. Macom is one supplier. I didn't look at their website for the most appropriate part (that's your job), but here is one that is a bit higher capacitance than you require. Skyworks and other manufacturers also offer this kind of part.

The 10:1 capacitance range you are asking for is probably not quite achievable, but perhaps you can relax that requirement.

If you put multiples in series (for RF) and parallel (for DC) you'll end up with no greater range (probably less) and (and because of) more parasitic capacitance (especially to ground. You may be able to make that work in whatever you have in mind.

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  • \$\begingroup\$ Thanks for this information...I already read as you mention here MA46H120 Varactor diode.But the range of capacitance is 0.14pF to 1.1 pF ... for my project i required lower range of capacitance...like 0.01pF to 0.5pF?? so there is any varaible capacitance available of this range? \$\endgroup\$ – ravi Apr 22 '15 at 13:30
  • \$\begingroup\$ Well, it's close. Perhaps you could talk to them. Even if you could put two in series you'd still have only 8:1 in range. Maybe you should re-examine the approach if it seems to require parts that nobody can manufacture. \$\endgroup\$ – Spehro Pefhany Apr 22 '15 at 13:33
  • \$\begingroup\$ suppose when i connect varactor diode and the inductor in parallel. so how its work?? And what is the effect of phase when we change the value of capacitance?? \$\endgroup\$ – ravi May 13 '15 at 11:42

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