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What is the difference between ASIC and FPGA?.

Discussion in 'Electronic Design' started by [email protected], Jan 16, 2005.

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  1. Guest

    Hello, I have two questions about Electronic circuit board design.
    These are the questions:

    1st question:
    What is the main difference between FPGA and ASIC, recently I went to
    some exhibition, there I heard from somebody, he says "we are designing
    a prototype handset based on FPGA, which was used between DSP chip and
    main processor, later on we will go wityh ASIC", I didn't understand
    quite well, what was the main difference, also whereever FPGA was used,
    can that be replaced by ASIC?.

    2nd question:
    What are the main stepps involved in circuit board design?. Suppose if
    I want some board to be designed, what are the steps I have to do (like
    a fabless design), how can I contact the fab to get my prottype board
    as well as production baord?.

    Thanks in advance, appreciated.
     
  2. Tam/WB2TT

    Tam/WB2TT Guest

    An FPGA is a Field Programmable Logic array. As the name implies, it can be
    programmed to be anything within its capability. ASIC stands for Application
    Specific IC. In his context, he means a custom IC. So, the FPGA is a
    prototype for the final version. You don't make one ASIC, you make
    tens/hundreds of thousands.

    Tam
     
  3. Guy Macon

    Guy Macon Guest

    Minor correction: An FPGA is a Field Programmable Gate Array.
    ^ ^^^^
     
  4. Ken Smith

    Ken Smith Guest

    Field Programable Gate Array: a bunch of logic cells that you can program
    to do lots of different things. One of these things would may be the
    thing you want done.

    Application Specific Integrated Circuit: a chip designed to do a certain
    job or a small group of jobs. If you want to do something else get a
    different chip.

    Basically it like this:

    You can make the prototype with very costly general purpose FPGAs, some
    DSPs, and have a cable running off to a big battery. This version costs a
    billion dollars each. Our target cost is 3 dollars so we will have to
    spend 10 Million on making a custom chip and sell about 4 million units to
    make it pay.
    1) Decide what the bourd should do.
    2) Make a schematic that does that.
    3) Decide the mounting issues.
    4) Select the component packages.
    5) Buy board layout software if you intend to do it yourself
    6) Start placing the parts
    7) Discover that they won't fit and loop back to 3
    8) Finish placing
    9) Start running the traces
    10) Discover that you can't route as placed and loop back to 8
    11) Finish routing
    11) Check the proposed layout
    12) Rip out large sections and loop back to 8
    13) Check the improved version
    14) Check it again
    15) Make Gerber plots and an NC drill file
    16) Check the Gerbers and drill file
    17) Compose a README.TXT
    18) Zip together the Gerber, NC drill and README.TXT
    19) Get bids on making the board
    20) Select a vendor and send off the files
    21) Get a phone call from the vendor pointing out an error
    22) Loop back to 11 and increase the ring on the vias etc
    23) Get the boards from the FAB house.
    24) Gather the parts needed
    25) Discover that you can't get the MOSFET in a DPAK loop back to 4
    26) Stuff the board
    27) Apply power
    28) Scrape the burning parts off your face
    29) Replace the burned parts
    30) Apply the right power the right way around this time
    31) Begin debugging the board
    32) Discover the errors that are not just part values
    33) Loop back to 1
    34) Prepair BOMs etc for the production build.
    35) Fight off the accounting guy who wants to lower cost.
    36) Make the pre-pre-production units
    37) Correct the BOM and assembly drawings
    38) Start testing the pre-pre-production units
    39) Build the pre-production units
    40) Do major testing
    41) Discover that the specifications from marketing have changed
    42) Loop back to 1
     
  5. Ken Smith

    Ken Smith Guest

    If you'd done it in an FPGA, no-one would even know you made the mistake.
    As it is you did it in an ASIC so you had to turn the design.
     
  6. keith

    keith Guest

    If I'd done it in an FPGA, I still couldn't stand up. My '70 Gremlin was
    small enough!
    They would have know it long before, when you wrote the check for the
    masks, the counters of beans would have noticed.
     
  7. Andrew Holme

    Andrew Holme Guest

    Development / debugging:
    An FPGA can be re-programmed again and again, until you get it right.
    An ASIC is hard-wired with a mask - you can't change it once it's
    fabricated!

    Power:
    An FPGA consumes more power than an ASIC.

    Cost per unit:
    ASICs are only made in large quantities - the total investment is large -
    but the unit cost is small.
    FPGAs can be used for one-offs, but would not be competitive in large
    voilumes.
     
  8. Mark Jones

    Mark Jones Guest


    This is good! We should put this in a F.A.Q. ;)




    -- "Welcome to the new millennium, where ingenuity is dead and
    SpongeBob Squarepants rules the world..." MCJ 200406
     
  9. Mac

    Mac Guest

    The first step should be a specification for the finished design. This
    might include mechanical specifications as well as functional and power
    consumption specifications. If UL and FCC (or similar) approvals are
    required, that should be part of the specification, too.

    Then I guess schematic capture would be the next step. Schematic capture
    just means drawing the schematic with appropriate software. Around this
    time you want to start making sure that you can get all the parts you are
    using.

    The next step would be layout. To do this, you have to decide how many
    layers the board will be, where the parts will go on the board, where you
    want to put fills and floods and so on. Any nets requiring special
    treatment might best be done first. At this stage you want to have samples
    of the parts on hand so you can compare the physical part with the layout
    you are doing.

    When layout is finished, you need to prepare the fabrication files and
    send them off to the board house. They can then give you a quote for what
    the raw boards will cost. Around this time you want to have all your parts
    in stock in quantities sufficient for the number of boards you will build.

    Once the boards come back, someone will need to solder all the parts to
    the board, and do any required mechanical assembly. Sometimes the raw
    boards are tested, either by the fabricator or by you.

    If you have limited personnel, you can contract out some or even all of
    the design. Or you could write the specification, draw the schematic,
    and write layout guidelines, then contract out the rest of the design
    and fabrication. But layout can be absolutely critical for some designs,
    so be careful!

    In general, if the design involves one or more of the following,
    layout might be critical: small analog (or RF) signals; fast digital
    signals; high voltage, power or current.

    I should re-iterate that if the finished product requires agency approvals
    (FCC, UL, etc.) then you will need to take that into account from the
    beginning.

    --Mac
     
  10. (Ken Smith) wrote in
    Here's a good tutorial about designing PCBs (minus all the real-world
    details given in the list above):

    http://www.pcb123.com/tutorials/PDF Documents/PCBDesignTutorialRevA.pdf



    --
    ----------------------------------------------------------------
    Dave Van den Bout
    XESS Corp.
    PO Box 33091
    Raleigh NC 27636
    Phn: (919) 363-4695
    Fax: (801) 749-6501

    http://www.xess.com
     
  11. Rich Grise

    Rich Grise Guest

    On Sun, 16 Jan 2005 11:51:37 -0500, Mark Jones wrote:

    Great Idea!

    Where's the FAQ?

    Thanks,
    Rich
     
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