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THVD8000: THVD8000 frequency division multiplexing

Chris Randall
Prodigy 10 points
Part Number: THVD8000

Tool/software:

Hi there

I see in the THVD8000 datasheet there is mention of a bandpass filter on the de-modulator input to the device. I have an application which currently uses two lanes of RS-485 (one for data, the other for a measurement synchronization pulse). I was wondering if it is possible to operate two pairs of THVD8000 on a single twisted pair running at different F_Set values. I assume this would work with a discrete bandpass filter on the input/output but was wondering if the in-built bandpass filter would be sufficient?

Kind regards

Chris

  • 0
    TI__Guru 73971 points

    Hi Chris,

    The internal bandpass filter isn't very narrow. So it may end up picking up the other frequency if they are too close to each other. The other problem is the frequency setting for the carrier frequency has a lot of tolerance (this is why the receiver bandpass filter is wide). So you end up with both the output frequency that could be up to 25% off from the target and something like 50% tolerance in both directions of the receiver being wider than expected. With this you could potentially overlap and end up picking up the other frequency. 

    We've seen one customer build their own discrete receiver for something similar to what what you're attempting which seems like they were successful. So it technically can be done but we generally don't recommend it. 

    The other potential issue I may be concerned about is if the two THVD8000s tried to communicate at the same time and had some contention. You may end up putting stress on the devices since they would look like a short circuit between the two outputs. You would need to try to come up with a way to avoid the two of them trying to transmit at the same time if they are sharing the same bus/cable.

    -Bobby