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DS90LV047A: Additive Jitter

Boris van Wessel
Prodigy 60 points
Part Number: DS90LV047A
Other Parts Discussed in Thread: SN65LVDS20, SN65LVDS31, SN65LVDS105, LMH7220, DS90LV001

Hello, 

For a high precision (<10ps) TDC application I am looking for a way to translate LVTTL and TTL signals to LVDS signals without adding alot of additive Jitter. 

I expect my input signals to have a frequency between DC and lets say 180MHz.

I was wondering about the amount of additive jitter (both deterministic and Random) I could expect by using the DS90LV047A.

Are there any alternatives to this part that could provide me with a better Jitter performance or potentially a smaller differential skew? 

a different approach ive had in mind was to use a high speed comparator to do the (LV)TTL to LVDS conversion in order to obtain the lowest amount of additive jitter and output skew. 

Do you have any experience/ ideas on using a comparator for low jitter TTL to LVDS conversion? 

Im looking forward to hearing from y'all. 

Thanks in advance!

~Boris

  • 0
    Guru 279390 points

    A differential input works like a comparator. So a high-speed buffer like the SN65LVDS20 (which is faster than any plain transmitter) is likely to have the smallest jitter.

  • 0 in reply to Clemens Ladisch
    Prodigy 60 points

    Hi Clemens, thanks for your reply. 

    I am not so much interested in the speed aspect, I am really trying to get as low of an additive jitter as possible. 

    I have checked the part you've mentioned, but it seems like the jitter expected by using it is greatly above my jitter limit needed to have a tdc resolution of atleast 10ps. (preferably less) 

    Thank you for sharing the idea of using the buffer, but I will continue my search <3

  • 0 in reply to Boris van Wessel
    TI__Genius 14601 points

    Hi Boris,

    Jitter tolerance is system dependent (sounds like your application requires very low jitter). In standard applications exceeding 20% jitter tends to close the eye diagram and corrupt the data. The DS90LV047A device was characterized with 20% jitter. The datasheet provides an overview section (9.2.2.2) of the test procedure (and results at 20% jitter, Figure 16).

    This application note (How Far, How Fast Can You Operate LVDS Drivers and Receivers?) has a breakdown of jitter measurements at 5%, 10%, 20% as tested bench level on the DS90LV047-48A EVM. If you are looking for say, a 5% jitter tolerance, see the “48” column of Table 1. This table does a nice breakdown of comparing other devices tested (DS90LV011/12A, SN65LVDS31/33, DS90LV047/8A). Additionally, I would also look into the SN65LVDS105 (SN65LVDS105).

    I put your criteria in our search tool: LVDS, M-LVDS & PECL ICs product selection | TI.com. Unfortunately, we don’t have a filter option to breakdown by differential skew, but it should be listed in the datasheets to compare. If you are looking for a high-speed comparator, the LMH7220 may be a fit.

    Regards, Amy

  • 0 in reply to Amy
    Prodigy 60 points

    Thanks Amy, this has been very helpfull. 
    I will be making a testprint with both the SN65LVDS105 and the DS90LV047A to see which component works best under my expected conditions.

    Have a good weekend!

  • 0 in reply to Boris van Wessel
    TI__Genius 14601 points

    Hi Boris,

    Thank you for the feedback, glad to hear you found a possible fit for your application.

    Please reach out if you have any questions. 

    Regards, Amy

  • 0 in reply to Boris van Wessel
    TI__Genius 14601 points

    Hi Boris,

    Just one other thought that I had for you:

    It is possible to use a LVDS buffer as a driver. Here is a TI application note: How to Use a 3.3-V LVDS Buffer as a Low-Voltage LVDS Driver (ti.com)

    The DS90LV001 has 100 ps of jitter at 800 Mbps. It accepts LVTTL signals and outputs LVDS. You could use high quality source for Vref for the inverting leg of the buffer to avoid injecting any other sources of noise.

    DS90LV001 data sheet, product information and support | TI.com

    Regards, Amy

  • 0 in reply to Amy
    Prodigy 60 points

    Hey Amy, 

    I appreciate you sharing this new thought with me, I find the concept very interesting. 

    Since I also expect TTL voltages at my input, I am more leaning towards the driver options you have helped me with. 

    I will keep this concept of using buffers instead of drivers in mind, it might come in handy some other day. 

    Thanks a lot and have a good day!

    ~Boris