Hi,
For a project I'm working on, I require an X band varactor, with a junction capacitance of the order of 0.1pF.
I am struggling to find a varactor (surface mounted, SC-79 packaging) with that low a junction capacitance, the best I have found so far is the SMV1430 by skyworks which has a junction cap. of 1.11pF.
Any help would be greatly appreciated.
I think you will find it difficult to find a solderable, lumped component that fulfills this requirement. Once you reach these capacitance values, even deviations in soldering and mounting will likely exceed the capacitance value. A small blob of solder will exhibit 100-200fF capacitance. Once you get into X band, varactor tuning is best done as part of an integrated MMIC (like an integrated VCO) where varactor package parasitics are avoided and interconnect performance can be tightly controlled.
If you are using a varactor as a discrete component for tuning a dielectric resonator filter or oscillator (DRO) , your best bet is to use transmission line elements to transform impedances so that you can use a device like the MAVR-011005-12790T. Keep in mind that parasitic inductance must also be accounted for (the MAVR-011005-12790T data sheet specifies 0.6nH for this device).
I have used the Skyworks SMV-2019 for tuning X-band phase-locked DROs with a minimum of fuss.
The MAVR-011005-12790T from MACOM is 0.27 pF. What are your voltage and current requirements?
I think you will find it difficult to find a solderable, lumped component that fulfills this requirement. Once you reach these capacitance values, even deviations in soldering and mounting will likely exceed the capacitance value. A small blob of solder will exhibit 100-200fF capacitance. Once you get into X band, varactor tuning is best done as part of an integrated MMIC (like an integrated VCO) where varactor package parasitics are avoided and interconnect performance can be tightly controlled.
If you are using a varactor as a discrete component for tuning a dielectric resonator filter or oscillator (DRO) , your best bet is to use transmission line elements to transform impedances so that you can use a device like the MAVR-011005-12790T. Keep in mind that parasitic inductance must also be accounted for (the MAVR-011005-12790T data sheet specifies 0.6nH for this device).
I have used the Skyworks SMV-2019 for tuning X-band phase-locked DROs with a minimum of fuss.
Dear Fraser,
I agree with George that the best choice may be very small area MOS capacitor that can work as a varactor capacitor. The circuit suitable technology may be the microwave monolithic circuit technology. As a discrete component it may be difficult to get such very low cap varactor. May be a possible solution is to use Tunable MEMS capacitors. You have to give the C-V characteristics of the required varactor.
An other partial solution is to reduce the value of the varactor capacitance is to connect a suitable fixed capacitor with it in series.
You may get more information from the paper in the link: https://pdfs.semanticscholar.org/4443/fda4d2ca730a4d26b447c08292aedbd8fdf0.pdf
Best wishes
I worked in the recent past in projects where we used varactors for antenna design with some stringent specifications. I found this model of varactor should satisfy your requests: MA46470.
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