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Help for 10mbit/s FSK transmitter and receiver

Discussion in 'Electronic Design' started by Oscar (X.), Nov 15, 2006.

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  1. Oscar (X.)

    Oscar (X.) Guest

    I have to design a fast 10mbit/s FSK transmitter and receiver. The
    frequency coding for mark and space can be chosen freely because the
    transmission is between two very close electrodes (electromagnetic
    coupling) and not across long distances in air. Actually I have some
    design options:
    1) ideally, a totally integrated solution (single chip which turns ones
    and zeroes into the corresponding frequencies, and vice versa). But
    I've been unable to find chips which were fast enough (I found
    something like 300kbps at most).
    2) I could use a PLL as a demodulator/modulator, but the TLC2933 is the
    fastest I found (100Mhz max operating frequency) and I seriously doubt
    that the loop bandwidth would be enough. Faster PLLs are usually
    intended to be frequency synthesizers (for the implementation of clocks
    and local oscillators) and there is no output pin for the VCO control
    voltage...
    3) probably I should find a PFD and a VCO separately if the integrated
    solutions are not good enough
    4) as a modulator theoretically I could drive a VCO directly, but it
    must be suitable for that (fast frequency stabilization, decent
    precision).

    Do you already know about good ICs/solutions for this problem?
     
  2. linnix

    linnix Guest

    "Oscar (X.) дµÀ£º
    "
    You could use the fastest FPGA (~500 MHz) and wide spectrum
    transceivers. Even so, I doubt you can go more than a few mbit/s. The
    technology is just not there, or is waiting for you to invent.
     
  3. Mark

    Mark Guest

    yep a free running VCO should be stable enough compared to 10mbps

    your talking about a signal with over 20MHz BW

    Mark
     
  4. Does it have to be FSK? Theoretically not impossible, but since you
    have choice of band and electromagnetic coupling, you'd be far better
    off going with something like a broadband solution.

    There are DSL modems that cost $25 OEM. You could cannibalize one of
    these designs, as they already support up to 24 mb/s uni-directional
    and do the bit-spreading for you. You'd only have to focus on
    interface circuitry.

    http://en.wikipedia.org/wiki/Digital_Subscriber_Line

    -Le Chaud Lapin-
     
  5. John  Larkin

    John Larkin Guest

    A stock VCO should do fine for the transmitter. The receiver could be
    a MMIC amplifier, a simple phase-shift network and a diode mixer,
    followed by a lowpass filter and a comparator. Probably you can do the
    whole receiver in a single chip, somewhere, if you shop around.

    Run at maybe 100 MHz or so with a pretty wide deviation.

    John
     
  6. Oscar (X.)

    Oscar (X.) Guest

    Le Chaud Lapin ha scritto:
    Technically I could choose something different from FSK... anyway the
    transceiver should be "invisible", i.e. there are 2 systems
    communicating via a wire, and they shouldn't notice if this couple of
    transceivers are placed at the middle of the wire. With FSK first I
    wouldn't have to bother about protocols etc., and then the
    communication must be "real time", unlike with many protocols like
    wi-fi etc.
    I don't think you can open a DSL modem and identify a subsystem which
    transmits the data and another separate subsystem which cares about the
    protocols... probably there are integrated modules which do these two
    things at the same time, anyway I could try and see.
     
  7. Since you mentioned 10 mb/s, I figured that you were making an Ethernet
    link. If that is the case, then you would simply plug the Ethernet
    cables into each modem, put phone wire between the two, and be done. I
    do not recall if there is a "cut-through" mode for DSL, but there might
    be.
    It's not very elegant, but if you were to take the signal just before
    the line amplifiers for each modem and up-convert them to an
    appropriate frequency, you might just get away with this. The modems
    already have state-of-the-art forward-error-correcting schemes in them,
    so if you lose a frame or two, it would happen rarely if you have taken
    care in doing coupling and shielding.

    Also, a circuit based on free-space optics might be a consideration.
    After all, if the couplers are that close, then you are almost
    guaranteed good performance.


    -Le Chaud Lapin-
     
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