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Silicon delay lines

Discussion in 'Electronic Design' started by [email protected], Apr 2, 2007.

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  1. Guest

    Is it "good practice" to design with delay lines? I assume somebody
    must be buying all those 74ls31 and DS1100s.

    Anybody ever used some of these and for what? Just curious.
     
  2. John  Larkin

    John Larkin Guest

    Good practice is anything that works.

    Delay lines can be very handy. The LS31 is pretty sloppy, but there
    are more precise parts around, like the Dallas thing... Bel Fuse and
    Data Delay have some too. Micrel makes an astonishing ECL delay line,
    SY89295, which has 1024 internal 10 ps delay elements and guaranteed
    monotic setability.

    We program delay lines inside FPGAs now and then; you have to fight
    the Xilinx tools to do it. Some of the new Vertex chips include
    legally-sanctioned delay blocks.

    All-synchronous design is sort of a severe ancient religion.

    John
     
  3. Guest

    Guess so, as long as you know what you're getting into. I've got this
    personal thing that's been bugging me like a splinter under a
    fingernail for a while.
    I'd like to try a delay line, but I'm wary of things I don't
    understand. Want to learn, you see.
    If only Digikey carried them. I hate specifying parts that other
    people will have trouble ordering. And I don't want to be in the parts
    business.
    Ah yes, Micrel. A bit too much for a 32MHz CMOS clock...
    No PLDs in my design. Just a few flip-flops and a PIC.
    Heh.
    I'm planning on some pretty good power supply bypassing on the delay
    line chip. I understand there's some kind of ramp/comparator thingy in
    there. I'm hoping that overall it's less sensitive to power supply
    noise than the VCO I've got right now.
    Would you heavily filter the VCC to a delay line?
     
  4. Joerg

    Joerg Guest

    I never do and have designed some out. Got less noise that way and the
    BOM cost total plummeted impressively. The latter made that client
    really happy. They were kind of expecting that I'd solve their noise
    issues and later didn't really want to know why the noise was now gone.
    But they sure didn't expect a serious cost reduction, especially because
    it just "happened" they didn't have to pay extra for that service.

    If, for example, there had to be a precise summation of signals over
    staggered delays I used Belfuse LC lines as John mentioned. For anything
    else it's the good old LC, RC, LR, whatever is practical. IOW nickel and
    dime parts. Then again my background is analog so maybe I am a bit
    biased here.
     
  5. Joel Kolstad

    Joel Kolstad Guest

    Sure... I used some DS1000-series delay line (and some logic) once to create a
    double-speed clock to extract bytes from a 16-bit word-wide parallel data bus.
    The clock speed was fixed, the DS1000 part had decent tolerances, so after
    sitting down and checking the timing margins, it really was a solid,
    repeatable design.

    In fact, the main advantage of something being sold as a delay line over just
    using some handful of spare gates is -- generally -- the much tighter
    tolerance you get on the delay.
     
  6. Guest

    "NOTIFICATION OF DISCONTINUANCE
    END OF LIFE: DELAY LINES
    ALL PRODUCT FAMILIES

    Bel is issuing this Notification of Discontinuance regarding the End
    of Life status of our delay line products. This unilateral
    discontinuance is in support of rather than in lieu of any prior
    notification you may have received from Bel. Original notification
    dates are in no way superceded by this announcement."

    Oh dear. I suspect 100000 transistors on an ASIC are cheaper than a LC
    delay line.
     
  7. Joerg

    Joerg Guest

    Yeah, mine had been a long time ago. They were used in ultrasound
    beamformers (that's what I often design for a living). Then, with
    digital beamforming becoming economical the market for delay lines has
    shriveled to the point where it just doesn't make sense anymore. But you
    can still get similar delay lines from others. Be prepared for sticker
    shock though. IMHO these have become boutique parts. While it may be ok
    to use one in a rocket controller it might not be the right thing to do
    in regular electronics.

    As I wrote, personally I'd stay away from a "canned solution" and roll
    my own. It ain't that hard. Heck, we even roll our own pizza dough
    instead of buying anything "ready to bake" :)

    Besides noise and a painful sticker price there is another reason why I
    avoid commercial delay lines if at all possible: Neither I nor my
    clients like single-sourced parts. Over my career I have heard the
    clanging of too many last order bells and seen the demise of whole
    companies along with their otherwise superb products. Remember Plessey
    and their excellent mixer chips? Luckily I was able to secure a small
    stash of those before the ship sank.
     
  8. Guest

    Monostables have ramps and comparators and can have nasty
    sensitivities to noise. Some of the Dallas parts that Dallas list as
    delay lines are actually strings of monostables.

    Proper delay lines don't have ramps and comparators, and are much less
    noise sensitive. I've used them in a few applications, but they do
    tend to come out expensive.

    Farnell stocked the Newport lumped constant delay lines for some
    twenty years - they were still in the catalogue last year, albeit as
    C&D Technology parts - but they've vanished from the 2007 catalogue.

    These parts were just passive linear phase phase low pass filters,
    built as thick film hyrids, and - as passive parts - they were totally
    insensitive to power supply noise. If you get hold of a book on filter
    theory, you can design your own delay line as an "all-pass" filter,
    but you get twice as much delay out of the same capacitance and
    inductance if you design your delay line as a low-pass filter. You do
    have to make sure that the high frequency cut-off of you low pass
    filter doesn't excessively slow down the transition times of the wave-
    train you plan on delaying.
     
  9. Joerg

    Joerg Guest

    You can still get those types of delay lines today:
    http://www.susumu.co.jp/english/pdf/products-j05-01.pdf
    http://www.susumu.co.jp/english/pdf/products-j05-02.pdf

    Digikey has that series in stock. But sit down before looking to the
    right where the prices are. Big bucks. Key "Susumu" into search, then
    first item under "Inductors".
     
  10. Ian

    Ian Guest

    It's the other way round, you get twice the delay of the low-pass
    version using the components as an all-pass.
    You probably wouldn't like the shape of the output edge, though;-)

    Regards
    Ian
     
  11. Guest

    That's not the way it seemed to be working when we looked into this at
    Cambridge Instruments around 1985 - which is why we went ofr the low-
    pass filter.
    A phase linear low pass filter may degrade the steepness of the output
    edge, but since the delay will remain constant with frequency up to
    the cut-off point, it won't degrade the shape.

    A phase linear all-pass filter wouldn't - in theory - have a cut-off
    point, so it ought to be better.
     
  12. Fred Bartoli

    Fred Bartoli Guest

    a écrit :
    For a normalized 1st order APF Hap= (1-p)/(1+p)
    For a first order LPF Hlp= 1/(1+p)

    The APF has twice the LPF phase shift for the same cut off frequency.
     
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