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DS280BR810: Various DS280BR810 Questions

Daniel Jackson
Intellectual 575 points
Part Number: DS280BR810

a) Is the version of the DS280BR810 datasheet dated November 2015 the latest version available?

b) Is the version of the DS280BR810 Programmers' Guide dated (last revised) December 2015 the latest version available?

c) Does DS280BR810 support use of single-ended inputs (e.g., except perhaps for proper LOS detection) (note that the datasheet of a competitive device, the HMC6545, explicitly states "The inputs and outputs... can be operated either differentially or single-ended")?

d) When the DS280BR810 is operated in FIR limiting mode, what input signal minimum amplitude is typically supported?

e) What is the typical DS280BR810 differential input low-frequency common-mode impedance (e.g., 2.5 Ohms, 25 Ohms, 250 Ohms, 2.5K Ohms, 25KOhms,...)?

  • 0
    TI__Mastermind 43795 points

    Hi Daniel,

    a. There is a newer version which can be requested through the product folder interface.

    b. There is a newer version which can be requested.

    c. The DS280BR810 is designed to be a differential device.  Single-ended operation is possible but not specified.

    d. The signal detect function requires a > 200mV Tx launch amplitude.  Increasing the launch amplitude to 600-800mV is optimal.

    e. The common mode return loss is better than -7 dB at 100 MHz, this was the minimum test capability. This value can be extended to lower frequencies.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Intellectual 575 points
    Lee,

    d) If signal detect (that is, LOS detect) is not a concern (i.e., if the channel is configured to not squelch the output based on the size of the input signal), how small can the input amplitude be? From another point of view, in FIR mode what is the maximum gain that the channel could successfully apply to regenerate the input signal?

    e) The input common mode loss is not a concern here. The input common mode impedance is the concern.
  • 0 in reply to Daniel Jackson
    TI__Mastermind 43795 points

    Hi

    Our maximum channel extension is quoted as ~17 dB in the datasheet.  What are you planning to drive this device with?

    The common mode is AC coupled so the impedance will increase as the frequency drops below the normal range of data.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Intellectual 575 points

    Lee,

    So that sounds like a maximum gain possible of about 7.

    The application involves receipt of a differential signal in over a cable, with the signal needing to be regenerated to perhaps 1000mVdpp, with the incoming signal amplitude possibly as low as 100mVdpp, perhaps lower.  (As noted, squelch detection is not a (major) issue, and could be disabled in the IC.)  Limiting (FIR) mode is required, rather than linear amplification of the input signal.

    Prior to highspeed scrambled signaling occurring at 10/20Gbps, PCIe-like "RX Detect" signaling can occur, wherein the low-frequency input common mode resistance is checked (as a means to determine whether a far-end receiver is present) by the far-end transmitting device using a signal pulsing technique (the series coupling capacitors in the IC are not a (major) issue).  Hence the need to have an idea of what the low-frequency input common-mode resistance of each input port is.  The datasheet indicates that there is a 100 Ohm differential termination present, but some idea of what the ("stray") common-mode resistance is, is needed.

  • 0 in reply to Daniel Jackson
    TI__Mastermind 43795 points

    Hi Daniel,

    The gain will vary based on the specific frequency in question.  At nyquist (~12.5 GHz) the gain is over 20 dB.

    This device will not work in PCIe Receiver Detect applications.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Intellectual 575 points

    Lee,

    I believe it is possible to augment the inpout configuration of the basic device so that it will in fact perform satisfactorily in the required PCIe RX Detect situation.  For that, it would be helpful to understand what the low-frequency input common-mode impedance of the ports is.  Note that one possible response could be "infinite" (a purely 100 Ohm differential impedance being present), but something a bit more substantive would be highly helpful and appreciated.

  • 0 in reply to Daniel Jackson
    TI__Mastermind 43795 points

    Hi Daniel,

    The input differential impedance is ~ 100 Ohms.  The common mode impedance at DC is >50KOhms. 

    We have attempted to run this device in a PCIe environment and found external additions to the common mode did not create a robust receiver detection solution.

    Regards,

    Lee 

  • 0 in reply to Lee Sledjeski
    Intellectual 575 points

    Lee,

    I greatly appreciate your providing the information regarding the DC common-mode impedance.

    I also appreciate understanding what your PCIe-related experience has been; thanks.