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Wireless RF IC's

Discussion in 'Electronic Design' started by Jon Slaughter, Nov 3, 2009.

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  1. Are pretty much all modern transceiver IC's the same as far as the
    circuit? All the ones I have looked at recently use a crystal and
    some passives for the antenna which I assume are for
    impedance/resonance matching?

    Obviously the IC capabilities are different and the impedance matching
    techniques are too but basically it seems pretty simple circuit wise?
    Hardest part being the antenna(After all, thats really all there is).

    So, for the most part I can be pretty ignorant about all the special
    transmission techniques and concepts(QAM, SSB, ISM, etc...) and still
    do wireless very easy using these IC's? As long as I get the antenna
    approximately right and hook up a uC/P then I should be able to do
    some wireless(may be degraded but...)? Seems like it from what I've
    read in the datasheets.

    Guess I'm just supprised that it would be that easy but I suppose the
    IC pretty much takes care of everything? (as far as just bit banging
    is concerned)

    Also, how does one deal with interference. In the 2.4Ghz range I'd imagine
    it would be a huge problem? I'm looking at the

    Which has Zigbee and operates from 2.4Ghz to 2.483Ghz with 5Mhz between
    channels. Hence I guess there is a maximum of about 16 channels. I know that
    there are special techniques to deal with it but generally how does it keep
    thousands of different signals on the same band? (Since so many users use
    this channel(cell phones, mobile stuff such as laptops, zigbee devices,
    etc...). Is it all really in the DSSS technique and the channels are quite
    noisy or what?
  2. Nico Coesel

    Nico Coesel Guest

    IMHO I'd avoid the ones that need an external SAW filter. These
    filters attenuate about 10dB in the pass band which cuts sensitivity.
  3. It doesn't really matter now. I didn't know you had to get FCC approved to
    do such things ;/

    Is a real cheap modual(10$) that, I think, has zigbee support. While I'd
    rather do my own using TI's cc2480, which seems to have a ton of features, I
    didn't realize it would cost me 10-20k to actually commercially use it ;/
  4. Nico Coesel

    Nico Coesel Guest

    ??? Over here there are unlicensed frequencies which may be used
    without any form of paying fees. Ofcourse accountability for causing
    too much interference still stands. You probably need FCC / UL
    approval to sell a product in the US, but that is another case.
  5. Yes but my product will be "commercial". i.e., it will be sold(not in large
    quantities though... maybe 100/yr). How can I justify making spending
    10-20k$ just to add wireless capabilities and only make potentially a few
    thousand? Makes no sense. I can't understand why it would cost so
    much(actually I'm not sure the cost but this is what I found someone else
    saying) when the IC itself has already been FCC approved and the antenna is
    really the only additional RF component. It should be allowed that if one
    follows spec given in the datasheet to be ok.

    Under a certain power limit and over a certain frequency it should be free
    for commercial use since the range is extremely limited.
  6. yes, as I mentioned the one I was looking at.
    To me it sounds mainly like a way for them to get money(assuming those costs
    are correct). If some company fabs and ic and creates a certain for testing
    it and that circuit passes the FCC's tests then that circuit to almost exact
    specs(anything within reason) should be valid. The main issues are mainly
    with the antenna design and the IC and just common sense with proper layout.

    If it is so critical to keep noise down then they should designate a band
    for commercial use but free to use without restriction. This way you use at
    your own risk. The only requirement is that proper IC's and lay are used.
    You can't enfore the layout but if the IC is correct then it should do most
    of the job. Cause, after, all, what is preventing from someone not getting
    certified and designing a good circuit?

    The point being, is that some reason should prevail(but never does when
    money is involved). Simply making a "one size fit's all" rule isn't very
    practical. I understand their "goal" is to provide clean wireless comm but a
    little bit of reason can go a long way. How bout the makers of the circuits
    supply the model pcb layout that they used along with all the necessary
    specs(pcb dielectric, passive values, etc.) and only modifications unrelated
    to the rf section can be chained? Is that unreasonable? The devices could be
    restricted to only be used on private property and not for roaming and also
    for non-critical devices. This way it can be used on by businesses for their
    own use. Because of the short distances it would be highly unlikely to cause
    any drastic problems even if someone did screw something up big time.

    If a device is limited to around 50m and even 90% within spec I doubt much
    harm can come from it?

    Of course I'm just learning about rf and maybe any slight change, such as
    being 0.1% off on some passive's value, might cause some interference with
    some plane 30k ft in the sky? Of course, then again there will always be
    some genius to FTUBAR.

    If it really is an antenna problem then one should be able to by self
    contained FCC compliant antenna modules and then combine them onto the pcb
    with their own design based around an FCC complaint IC's with no big
    issues(here then it's only a connection matter and one of ground plains and
    coupling cap's).

    Somewhere there has to be some compromise. It seems to me, ignorant as I am,
    that it's mainly just a "tax" on companies that develop any RF device. After
    all, its a company so they can afford it and/or just pass on the cost to the
  7. Hammy

    Hammy Guest

    I was looking into this as well. Linx says FCC testing is about $5k
    for Tx and Rcv.

    They have a pretty detailed pdf here about FCC testing.

    Another useful place is Micrel lots of appnotes and info if you
    haven't already found it.
  8. If the circuit is is virtually the same(no major major modifications) as the
    one that was used by the IC manufacturer for their FCC testing and if it
    passed then it should pass for all time. This is like saying that every
    single circuit board must be tested because slight changes could drastically
    change it's behavior. That simply isn't the case... or if it is they still
    allow it. It is the design that is important(which I'm including the
    physical layout) rather the exact device. They obviously understand this to
    a degree.

    They do allow "minor" modifications as I just found out without requiring
    any notifications.

    Ok, but then thats not following the original design spec. Unexpected
    cross-coupling? Parasitic reactances? If the circuit is routed by exactly
    what was used by the IC's fcc testing(which had to have such a circuit to
    test with) then it should behave almost exactly the same. Obviously there
    will be minute differences and some things could potentially make a big
    difference such as dielectric of the pcb. But basically if you copy their
    design on the RF side then it should pretty much be functionally equivalent.
    Any actual differences shouldn't cause any real problems.

    Your not changing the length. Or, if it is a separate IC and antenna as I
    mentioned somewhere, the FCC could specify a maximum allowed distanced.
    (which is based on the original design)
    Yes, but I'm not talking about RF from scratch. I'm basically talking about
    copying an already proven design.
    Well, since the design was done by some TI guys then it is good enough? So I
    have to waste money to simply duplicate what they have already done? Hence
    the "scam". If I were to get their exact gerber documents and used the same
    components listed in their BOM(in the datasheet) then I haven't changed
    anything except possibly the pcb thickness/dielectric and copper thickness.
    Obviously I could use the wrong valued cap, for example... but that could
    potentially happen with a certified design when reproduced.
    An inch pretty big. If you've changed something like that from spec then
    it's not really an unessential modification. If the band is only for
    commerial unlicensed use then I would imagine medical sensors should not be
    using it. As I said... non-critical apps such as your TV communicating with
    your comp.

    Again, I don't know a lot about RF and I realize the potential for major
    problems. My point is that if you are basically copying the original design,
    which is FCC approved and the band is for non-critical use then it shouldn't
    be an issue. Given that the range would be only, max, a few hundred feet
    LOS in 2.4ghz at 0.1dBm at most, if someone screws up or intentionally makes
    major changes, then it will only effect things in that range. If it becomes
    a serious problem, say they overpowered the device, then the FCC will come
    in as normal and be able to see what they did and that they made changes
    from original spec and fine them.

    I just can't imagine, for example, if I took TI's gerber(they give the
    copper layout in their datasheets) and BOM and follow the rules given in the
    datasheet(after all, they want you to pass the tests) that I'd be so far off
    to cause any problems at all. It might not be as efficient but I doubt it
    would fail any tests.

    Of course, again, there are people that can't even tie their shoelaces but
    somehow got a degree in engineering... so...

    But again, I'm basically ignorant on the subject. I just feel that it can't
    be too critical to design such a thing... one because relatively speaking,
    it is a very simple circuit just from the number of components and layout.
    Second, the manufacturers pretty much tells you exactly what to do.

    Am I wrong to assume that if you follow there method to the T and don't make
    any blunders that you could bring down the space shuttle?

    Hehe, well, thats a pretty significant error. Huge relative to what I'm
    Then there should be a "Free" band. That people can use at their own risk
    and not critical. Say I make a design and follow spec's exactly but old joe
    engineer wants to cut costs so he uses some cheaper caps but at the wrong
    value. Joe sold some products that were used in the same location as mine
    and it caused mine to screw up... since it's non-critical it's no big deal.
    Obviously something is wrong. At some point the FCC comes out and then gets
    one of Joe's devices and find out what he did and fines him.
    A lot of things have changed though. Back in the day you didn't have
    integrated RF modules that did 90% of the work. In those cases it was much
    easier to screw stuff up.
    True... I guess that is the job of any government. But they shouldn't stifle
    entrepreneurship or small business growth nor techological advancement...
    that is, if it's not going to cause problems.
    The product recalls is the companies responsibility. If I only have 100
    devices sold a year then there is not much recall.
    Hehe... well, as I said... I really don't know enough about it. I'm just
    venting my frustration. I really wanted to implement my own RF device for my
    new nifty little widget to give it some very competative features. Luckily
    I have found some RF modules that can do the trick but they are a bit

    The main point is that I see a logical gap in the regulation. Basically it
    is overregulated to some degree. Regulation is good in moderation but there
    is such a thing as too much. But as I have said many times... I know very
    little about it. But the ideas I have stated are either wrong or right(for
    hte most part). If I were to produce an exact copy of the fcc tested design
    then it should behave exact. (I know, nothings exact) What the FCC could do
    then is allow for a quick test of the device for a much lower cost and or
    create a band for such non-tested or "quick-tested" devices.

    The IC's and design used would have to be fully tested and would be the
    responsibility of the manufacturer. But any "exact" implementation of that
    would then fall under that testing and only a simple "compliance" test could
    be required(or none at all if a proper spec for the band exists). The IC's
    could have a "compliance" test mode which would create a test situation so
    that the testers would have to do very little work. Would probably take < 5
    mins to do such a test.

    The results could be compared not only against the FCC's requirements but
    against original chips spec. If they are not with reason do to component
    variations then it could be rejected.

    Again, my point is simply that the situation could probably be improved
    unless I'm missing something that invalidates my logic. (in theory it makes
  9. My experience with the FCC is that there are two distinct parts. The
    You might be right. I thought I saw in several datasheets the mention of FCC
    "compliance". But even though it might not be necessary it is "necessary". I
    can't imagine a manufacturer creating a RF IC and not getting it tested
    since it has to be tested by the end user anyways.

    Hence it might be better to push all the work on the manufacturer since they
    have to go through it anyways. They could then just give the
    schematic/gerber files for the design and as long as you don't deviate then
    it should fall within compilance.

    I mentioned to dave that maybe the FCC could create a "utility" band that
    was unlicenced by only used by FCC licensed IC's. The IC's would be tested
    and you could only use the design by the manufacturer(the one the FCC tested
    of course). The band would not be for critical communications and the IC
    and design should elimintate any issues with interfering with other bands.

    Optionally they could enfore a cheaper method of compliance where the IC's
    would be required to run a compliance mode(say simply by toggling a pin). It
    would run an FCC approved test that could be completely automated. The
    results could be compared to the original design's results and the FCC's
    requirements. This should be enough solve any real issues involved.
  10. Thanks, that clears up some. I guess cheaper(about 5k instead of 15k) than I
    thought. Still quite expensive IMO. It's not like I'm desigining an
    tranceiver from discrete components ;/
  11. Of course not but I imagine I could get it tested relatively easy(local
    college or some EE type of shops).

    I guess you could be right that if the manufacturers suggestions/design is
    on the edge then it is possible to produce something that is out of FCC
    spec. Again, it would be nice if the FCC created a band that was for
    non-critical use and for used only by licensed RF IC's. The manufactuer
    would simply deal with all the design and compliance testing and as long as
    you implemented "exact" what they did then it shouldn't be a problem. The
    FCC would come up with the minimum requirements and require the IC to have
    some "test" feature that would automate testing.

    The IC's could be pretty stringently controlled so that even your average
    doofus couldn't screw it up too much and still be within compliance.

    What I feel is that the rules are still based on the old discrete methods
    where design was critical and involved many variables. With the IC's there
    are basically only 2 components. The IC and the Antenna. The IC is pretty
    much self contained. The Antenna could be critical but as long as the user
    followed the spec decently it should be relatively safe.

    To me it is just almost completely redundant. If the manufacturer creates a
    design that passes spec well(I'm sorta assuming this though) and I implement
    that design, then because it is so simple(being just a few components) that
    it would be hard for me to screw up. (basically if the manufacturer gave the
    schematic/gerber files and you just copy and pasted... I think you would
    still be within spec even if degraded).

    As I said, if the IC's are designed with such a test feature then the FCC
    could require a compliance test but it would be much cheaper since it would
    all be automated and the results could be compared to the manufactured
    results. Any anomalous results would result in a failure.

    If that is still a problem(non-critical, manufactured to compliance, forced
    tested) they could further specify such things as low power, short distance,
    low devices, low data rate or comm rate, etc. The idea is to open up the
    market for very cheap wireless devices for simple non-critical

    Of course, Is suppose if it is free then it will be abused and you would
    have people overpowering devices just to get into that band. Hence I guess
    the forced testing would be the way to go... but it probably could be done
    really cheap and require just minutes. A test point which initiates the test
    mode(as specified by the FCC) but also sends some manufacturer and IC code
    so they can pull up the original results to compare to. Then it goes
    through whatever output characteristics that are needed(I guess whatever was
    originally used) and compared to the original results along with the FCC
    band requirements. I'm sure it could be for around 100$ instead of 5k$.

    I'm not sure if the manufacturers would go through the trouble but I think
    it's a good idea ;)
  12. Nico Coesel

    Nico Coesel Guest

    Amplifier = extra noise (less sensitivity) + power consumption.
  13. JosephKK

    JosephKK Guest

    Type acceptance and type approval are both long gone (over 20 years
    gone). Currently it is handled with a "Document of Conformance" from
    a lab they regulate.
    What part of the FCC has had to become an income source instead of a
    money hole is so hard to understand?
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