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PCB power planes?

Discussion in 'Electronic Design' started by Martin Griffith, Jul 5, 2008.

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  1. I get the same triangles, silly idiots for letting something out like
    that in a ref. design.
    I don't think I need all the extra bits, just 1 vid in and an AVR or
    8051 to control it, so I was just going to have a vdd and gnd copper
    flood on the inner layers, get some cheap boards done to test.


    martin
     
  2. Rich Webb

    Rich Webb Guest

    Yes, with both the Foxit and PDF-XChange viewers so it's probably in the
    original.
     
  3. Eeyore

    Eeyore Guest

    Yup, looks odd in V7 reader here.

    Graham
     
  4. Eeyore

    Eeyore Guest

    Except when it's audio of course and you don'y want digital return
    currents you can hear in the audio ground. In which case pkysically
    separated but carefully linked planes are the way to go in order to
    direct the currents where you want them to go rather than randomly
    anywhere.

    Graham
     
  5. Joerg

    Joerg Guest

    Weird. But I'd be a lot more concerned about figure 5.2. Splitting
    grounds is rarely a good idea. Might also blow the EMC cert.
     
  6. Ha.. I remember a student who said he could make a small audio desk
    with the equalisers using MF10's.
    Never saw him again....I wonder why?


    martin
     
  7. Eeyore

    Eeyore Guest

    Was that the NatSemi ? switched capacitor filter ?

    No surprise there !

    Graham
     
  8. Eeyore

    Eeyore Guest

    Depends how you treat them ! Respect pays dividends.

    Graham
     
  9. Joerg

    Joerg Guest


    Even a nice application of Olde English furniture polish won't help :)

    Can you tell that to the current generation of kids?
     
  10. Joerg

    Joerg Guest

    You can design rather excellent audio gear with S/C filters. BTDT. Ok,
    not audio but audio range. It was a Doppler receiver for medical
    ultrasound. Zero through about 25kHz, dynamic range from here to the
    Klondike. Noise from clocks and stuff: None. Sold like hotcakes, still
    in use.

    The only reason why S/C filters fell from grace with guys like us was
    cost. They probably tried to maintain fat profit margins and that backfired.
     
  11. Joerg

    Joerg Guest

    Actually they are. You can get a TMS320 for less than four bucks. But
    mostly I did go back to continuous time filtering. When it had to be
    flexible sometimes heterodyne schemes. Mix to wherever filtering is easy
    (meaning cheap ...) and then back.

    Then there is the lost art of wave digital filters. Only few people know
    it and you can get away with very cheap uC sans HW-multiplier.
     
  12. That's not my experience. Switched cap filts are famous for clock bleed
    through, and you need to be sure your circuit can tolerate this. The clock
    frequency is usually an order of magnitude or more higher than the filter
    freq, so you can usually filter out the bleedthrough with an RC.
     
  13. Joerg

    Joerg Guest

    Yes, you must filter that out. Sometimes. There are apps where spectral
    components above 100kHz just don't make a difference. Plus the supplied
    clock shall be squeaky clean. Marvelous concept but IMHO the marketing
    guys killed it. Tried to make a killing with margins and then the market
    kind of imploded around them.
     
  14. Joerg

    Joerg Guest


    It's around $5. Yikes!

    You can get a nice DSP for that kind of money.
     
  15. They get terribly expensive, even for non tunable filters. I've been
    using Frequency Devices single freq analog Bessels, and they run about
    $100 a channel.

    Krohn-Hite used to make an 8-pole tunable analog filter but it was bench
    gear, not an RC.

    I think the closest you're going to get today would be biquad stages that
    use resistors to tune them, and programmable resistors. At least that's
    an all IC approach, and you wouldn't need a billion-stage stacked switch.

    Aliasing inputs, by the way, can come from surprising sources. People
    tend not to think about bleed through on chopper amp clocks, for example,
    but it's there.
     
  16. Joerg

    Joerg Guest

    Look at the bright side: You can make really nice mixers and stuff with
    them. If they just weren't so darn expensive.

    If you use the R2R ladders of DACs you could make one around chips like
    these:
    http://datasheets.maxim-ic.com/en/ds/MAX274-MAX275.pdf

    Of course, then you'd be on the phone with Rebecca all the time.
     
  17. Joerg

    Joerg Guest

    That's the crux with DSP, they often can't do that. This is where wave
    digital filters come in handy but youngsters don't have the foggiest
    what that is or think it's some tuning device for a surfboard.
     
  18. Joerg

    Joerg Guest

    Shhht! Don't tell. Keeps us busy :)

    You need to select a processor that can do stuff like fetch, shift and
    shift-add in very few machine cycles, ideally in one. Should be 16-bit,
    too, but that's no big deal anymore these days.

    AFAICT after Professor Fettweis retired the usual happened. This whole
    research area became unglued and withered. It's sad, there is hardly any
    continuance in academia. That's what I like about working in industry,
    you continue the product lines whether you like it or not. Better for
    the customers.
     
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