• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 33 subscribers
  • Views 462 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Input Termination/Biasing network for DS25BR101

Jay Hardesty
Prodigy 100 points
Other Parts Discussed in Thread: DS25BR101, DS30EA101, DS30BA101

Given the absence of an input termination on the DS25BR101, I was wondering how best to bias the inputs to accept a single ended 75Ohm input signal (signal format is 3G/HD SDI Video).  Thus far, I have had fair success by AC coupling a simple coax signal source terminated via 75Ohm resistor to ground (termination resistor is placed prior to AC coupling caps).  I originally configured a DS25BR101 for a 75Ohm single ended input, however, the DS25BR101 has yielded much lower jitter output while also occupying far less board real estate (board real estate is extremely limited).  So I am very keen to sticking with the DS25DR101 if at all possible.

Any suggestions or comments are much appreciated. 

Thank you.

- Jay

  • 0
    TI__Mastermind 29635 points

    Hi Jay,

    The DS25BR101 was designed for 100-ohm FR-4 EQ applications. I wonder whether you will have better performance if you use the DS30EA101 instead and apply the cable extender chipset application circuit shown in Figure 4 of the datasheet (pasted below):

    Please take a look at the DS30EA101.

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Prodigy 100 points

    Hi Michael,

          Thank you for the suggestion and for pointing out that I had a typo in my original post.  My original post suggested that my initial configuration used a DS25BR101 for a 75Ohm single ended input, etc,.. What it should have said was that my initial configuration used a DS30EA101, the very part you have recommended (and not the DS25BR101).  So, I actually have been looking at this part, as well as the DS30BA101 chip. 

    I feel I should point-out that the coax input in this application is barely a couple inches long, using MMCX interconnects, serving as a board interconnect and not a multi-meter signal medium.  As such, you can see how a full on equalizer, such as the DS30EA101, is a bit overkill/unnecessary.  That fact aside, of these three parts the DS25BR101 has fewer passives requirements while being nearly half the size of the other two chips (9mm^2 vs 16mm^2).  This PCB real estate savings is very desirable in this application.  Additionally, when configured as per datasheet recommendations, both the DS30BA101 and DS30EA101 yield higher jitter characteristics on the output than what I am able to attain with the DS25BR101 chip.  

    So, for the reasons of smaller footprint/layout requirements, and better signal fidelity, the DS25BR101 is thus far a much more attractive part for this application and I would be very appreciative of any information pertaining to the proper termination of a single ended 75Ohm input signal.

    Thank you for all your help and suggestions.

    - Jay  

  • 0 in reply to Jay Hardesty
    TI__Mastermind 43795 points
    Hi Jay,
    The DS25BR101 can certainly work as you suggest. I use the DS25BR101 in the lab with AC coupling quite often. Since this interface is actually very short I don't see any negatives to the implementation you are describing.
    Regards,Lee