low range inductor

Discussion in 'The Projects Forum' started by kalpraj.m, Feb 2, 2008.

  1. kalpraj.m

    Thread Starter New Member

    Feb 2, 2008
    1
    0
    hello friends,
    i want inductor of 56pH n such a low inductors are not available. i dont know how to get them.
    if u know about it please reply me as soon as possible........
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    I've never seen an inductor available in the picohenry range. I think that at high frequencies, lead arrangement will easily give you that much inductance.

    Can you tell us what the requirement is for?
     
  3. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Can't believe I missed this thread before :confused:

    Great article in the link, scubasteve!

    However, I'll suggest that creating such an inductor on a PCB may not be the way to go, as it may be necessary to "tune" the inductor for a resonant circuit in the GHz range.

    Such an inductor might look like a very small inverted "u" or omega ( Ω ) in a piece of bare wire. The inductor can be soldered across a couple of "tombstone" SMT capacitors to provide a network that can be adjusted using toothpicks, or the like, while monitoring the performance on a network analyzer.

    Variable inductors of low L are relatively cheap to make from plain bus or enameled magnet wire. Variable capacitors are relatively expensive to purchase, although one can always use "gimmicks", or short pieces of flat tinned copper stock to change capacitance.

    Strange things happen in such extremely high frequency circuits.
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    If you Google "pc trace inductance per inch", you'll find that it is in the range of around 8-20nH per inch, depending on layout, board material, and stackup. With 8nH/in, 56pH would be 7 mils long. That's 0.18mm. 180 microns.:eek: Bare wire won't help much.
    If our OP would tell us why he needs that, maybe we could be of more help. He might be trying to resonate a 10nF cap at 213MHz, or something equally impossible.
     
  6. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    Sounds like a radio filter or part of a vco that absolutely needs to be implemented on quality microwave dielectrics or even an RFIC.
     
  7. miconos

    New Member

    Jun 23, 2008
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    The use of this size inductor is frequent in ~60GHz VCO's in RFIC design
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I remember the coffee can convertors, which had a VCO in the 2GHz range. The tuned element was a simple trace, to tune it you sliced off the edge to reduce the length while watching a frequency counter for the downcoverted frequency. Cheap, simple, and worked like a charm. If you went too far you soldered a short wire to the end of the trace and started over. This was a ham circuit.
     
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