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circuit design till 100MHz

Discussion in 'Electronic Design' started by [email protected], Jun 17, 2007.

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  1. Guest

    Where does this frequency range fall ..in high frequency design or low
    frequency design range. For designing the analog circuits till this
    frequency, to study the effect of the PCB traces and other circuit
    related stuff is there any reference?
    thanks.
     
  2. 100MHz is most certainly "high frequency", and signal integrity in PCB
    design will matter a lot.

    Dave.
     
  3. colin

    colin Guest

    these days with such small components,
    you can make traces so short,
    as long as you have a good ground plane
    and with such good low capacitance devices
    upto 100 mhz its almost like playing with audio used to be.

    depends what you are trying to do of course
    and trying to breadboard at 100mhz is a different matter,
    ofc theres still plenty of room to get into trouble,
    and pcbs do start to exhibit frequency dependant charecteristics at less
    than 100mhz if you have long enough traces.
    theres lots of old info on that with regard to making wideband 100mhz+
    oscilloscope amplifiers etc.

    2ghz can be a challenge,
    and my laser didnt like being modulated at 2ghz,
    ive not gone over 2ghz so far,
    unless you include harmonics,
    although my simple srd sampling head seemed to show harmonics quite a bit
    higher,
    I have no idea how acurate it was.

    Colin =^.^=
     
  4. Guest

    hi,
    i am designing some power amplifiers. i can see most of the capacitor
    after few MHz is dominated by its parasitic inductance.Similarly
    inductors become capacitors. Transformer is no more an ideal one. the
    magentic core also behaves erratic way. Do check the permeability vs.
    freq characteristics. Damn,the permeability is flat till only few MHz.
    I am looking for some references where these issues are discussed. i
    am happy enough if i can design working circuit till 100Mhz. I taked
    to these RF people. They just say do not worry yours is not high
    frequency, they say for 100Mhz, the wavelength is 3m, so you do not
    need to worry much about the hish frquency effects. I am not
    convinced. Is there any information regarding this where i can read
    more on it.
    kristo
     
  5. I have not ventured into high frequency design, even at this moderate
    level, but I found a lot of good information in application note AN47, for
    high speed amplifiers, on the www.linear.com website. It is a well written,
    comprehensive, and informatively illustrated PDF document. There are also
    references to other documents that might help.

    Paul
     
  6. Guest

    Thanks Paul. i am desparately looking for more references. I just need
    references to read. I want to learn the topic and master it.
     
  7. Fred Bartoli

    Fred Bartoli Guest

    a écrit :
    Listen to them again. I don't think they told you you won't suffer from
    non ideal components effects, but rather that you won't suffer from
    transmission line effects.
    IOW, you can consider your PCB tracks as lumped elements rather than
    distributed ones. It's not the same thing at all.

    As an example, an easily reached 1pF PCB track parasitics is only 1.5k
    at 100MHz.
     
  8. Guest

    Thanks Fred. I got your point.Is there any literature on it?
    Thanks.
     
  9. colin

    colin Guest

    If you look at an RF book it will probably go into more detail than you
    want,
    if you say why you are wanting to use cored transformers we can see if
    theres an alternative.
    the parasitic inductance of capacitors at 100mhz can be minimised by using
    smal value capacitors,
    that are physicaly smal too, and very short trace lengths, ie zero length.
    aim to make your 100mhz circuit the size of a small postage stamp.

    ive resorted to putting SMD capacitors through the hole of a 2 sided pcb
    before
    to reduce inductance, but thats not realy needed at 100mhz.

    it very much depends on what it is your trying to do, ie if its wideband or
    narowband.

    Colin =^.^=
     
  10. colin

    colin Guest

    if thats the one I think it is its excelent, its a bit humerous in places
    too :)
    gives good advice about grounding, supply decoupling, using short lead
    lengths, ground plane,
    sheilding etc, conecting scope leads too.

    Colin =^.^=
     
  11. Guest

    Thanks colin. Yup i really do not want to goto RF design. Having said
    that i also do not want to just design the circuit for low frequency.
    Is there an alternative for cored transformer?
     
  12. Marra

    Marra Guest



    Its hard enough getting audio to stay stable never mind megahertz !
     
  13. colin

    colin Guest

    that depends entirly on what you are trying to do,
    but the answer is - probably.

    Colin =^.^=
     
  14. MooseFET

    MooseFET Guest

    You should also ask your self why you don't want the transformer. You
    are likely to be better off using one if you are working with a wide
    band signal and need to change impedance levels or split or combine
    drives.
     
  15. Guest

    i cannot do wothout transformer. in my application i am using the
    transformer to couple the high frequency line into the power lines. i
    cannot do without it. But is there is some way to design transformer
    without core then it would be wonderful.
     
  16. colin

    colin Guest

    I gues you cant, however you can get cores wich go upto 100mhz or more,
    micrometals do them.
    the higher frequency the smaller the particles its made of but the lower the
    inductance too.
    guesing your bandwidth isnt that high, you can tune out the undesirable
    parasitics.

    Colin =^.^=
     
  17. Rich Grise

    Rich Grise Guest

    Just a nitpick: Technically, 100 MHz is "Very high frequency"; HF is only
    3-30 MHz, then VHF from 30-300 MHz, so I'd think either VHF construction
    techniques would apply, or broadband, which is even harder. =:-O

    Cheers!
    Rich
     
  18. When I read this:
    "We intend to supply useful high speed products and the
    level of support necessary for their successful application
    (such high minded community spirit is, of course,
    capitalism's deputy)."

    I almost wept. :)

    Thanks!
    Rich
     
  19. Joel Kolstad

    Joel Kolstad Guest

    Only to radio operators. :)

    Check out Randy Rhea's book, "HF Filter Design," which details filters up to
    something pushing a gigahertz! :)
     
  20. MooseFET

    MooseFET Guest


    What is the voltage of the power line? How much current is flowing?
    These will determine the size of wire that must be used for the power
    line.

    At 100MHz, you can use an air core transformer if you don't need a
    wide bandwidth. You want the primary and secondary to be tightly
    coupled to each other. Making a twisted pair or using a coax will do
    this.

    For air core, you need to calculate the inductance you need and then
    wind the coax or twisted to yeld that much. You won't want to
    resonate with anything less than about 22pF.
     
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