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Help for 10mbit/s FSK transmitter and receiver

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?

Reply to
Oscar (X.)
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"Oscar (X.) =D0=B4=B5=C0=A3=BA "

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.

Reply to
linnix

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

your talking about a signal with over 20MHz BW

Mark

Reply to
Mark

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.

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-Le Chaud Lapin-

Reply to
Le Chaud Lapin

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

Reply to
John Larkin

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.

Reply to
Oscar (X.)

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-

Reply to
Le Chaud Lapin

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