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DS15EA101 Transformer Coupling

Martin Schaeffer
Prodigy 20 points
Other Parts Discussed in Thread: DS15EA101, DS25BR110

Hi,


The DS15EA101 equalizer says within the datasheet that it does not support transformer coupling.  If transformer coupling is required for my application is there a method by which this device can be made to work?  It meets all of the other needs i currently have including the industrial range.  My application is a 1.2Gbps 8b/10b encoded data stream over a cable that can range in length from 1m to 25m.  If I add pull up resistors and AC coupling caps from the output of the transformer, does the equalizer device support that method of input?  Or even a termination impedance with AC coupling caps between the output of the transformer and the input of the DS15EA101?

If the DS15EA101 will not work in my application at all due to my need for transformer coupling, is there another industrial grade adaptive equalizer that will function for me?

Thanks

Marty

  • 0
    TI__Mastermind 43795 points

    Marty,

    I am always suspect of transformer coupling with high speed data.  Transformer bandwidth is often an issue as it can have a big impact on the adaption process within the CTLE.  From a structural point of view, adding a 1:1 transformer on the receive side of a cable could be ok as long as the termination and AC coupling requirements shown in the figure are maintained.

    If possible, using a settable CTLE like the DS25BR110 would provide a cleaner solution.  Depending on the loss characteristics of the cable, using a couple sense pins in the cable assy to change the setting between "short", "medium", and "long" cables would provide enough granularity to give good results.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Prodigy 20 points

    The transformer we are using has a 3db point at 1.5GHz, so we tend to have enough high frequency content. 

    Is a component available for "sensing" the amplitude or the cable length for setting short/medium/long?

     

    Marty

  • 0 in reply to Martin Schaeffer
    TI__Mastermind 43795 points
    The transformer sounds good. What is the part number? I'm sure it will help a few people out.
    The DS15EA101 input signal should be ~ 800mVpp for the adaptive EQ to work correctly.

    High-end cables have on-board EEPROM to help the system understand what is connected. Since you need the isolation, using a sense through the cable may not work unless there is a paddle card at the connector which could be used to return a VDD/GND tie and control the EQ setting on the DS25BR110.
  • 0 in reply to Martin Schaeffer
    TI__Genius 13475 points

    Marty

    The 'EA101 sets it's equalization by looking at the edge energy on the received signal, as a result, it is sensitive to high frequency rolloff.   If you do use a transformer, you may want to experiment with the drive amplitude to compensate for the additional loss that the transformer is introducing into the link between the driver and the equalizer.

    Mark

     

  • 0 in reply to Mark Sauerwald88474
    TI__Guru* 88835 points
    Greetings,

    DS15EA101 has two pins: CAP+ and CAP- that indicates the amount of equalization device is performing. Normally the value of this voltage is between -0.5V and +0.5V. The longer the cable or media the more equalization and this number goes toward positive. As Mark mentioned, you can experiment with drive strength and meanwhile monitor this voltage. The more the drive strength the more negative this number will be.

    Also, Pulse transformer has two parts with about 1.5G bandwidth(based on data sheet). The part numbers are: CX2040 and CX2038.

    Regards,,nasser