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TLV3801: Regarding single ended output application

Deepak Sharma
Prodigy 235 points

Part Number: TLV3801
Other Parts Discussed in Thread: TLV3601, SN65EPT21

Hi TI

The TLV3801 provides LVDS output, but our design necessitates a single-ended output with specific minimum and maximum voltage amplitudes for the toggling signal, as illustrated in the figure below. Could you please review the signal chain and advise on how we should proceed with the TLV3801, given that it perfectly matches the required transition time latency of our project, which is in picoseconds?

Kindly advise on devising a comparator to enable an RF SPDT to route either of the inputs to the output.

Thanks

Deep

  • 0
    Guru 325330 points

    You can either use a comparator with push/pull output like the TLV3601, or add an LVDS receiver like the SN65EPT21. Both are much slower. And the SPDT switch will have an additional delay.

  • 0 in reply to Clemens Ladisch
    Prodigy 235 points

    Hi Clemens


    Is it possible to synthesize a faster solution that offers a maximum transient latency of less than 1 nanosecond, utilizing either a push-pull output comparator or an LVDS comparator with an LVDS to TTL converter?

    Thanks

    Deep

  • 0 in reply to Deepak Sharma
    Guru 325330 points

    An LVDS output is designed to drive a 100 Ω load. When you connect an LVDS output pin directly to a high-impedance input, then the output voltage range might be larger. (But this is not guaranteed by the datasheet; you have to test, and it might change in future revisions.)

  • 0 in reply to Clemens Ladisch
    TI__Genius 11701 points

    Hi Deepak,

    As Clemens mentioned, we have seen TLV3601 be used to convert differential outputs to single ended outputs but unfortunately this adds a delay being that TLV3601 is in the 2.5ns range and minimum pulse width of 1.25ns. Sorry this is the best we could offer in terms of push pull comparators. 

    We do have a written piece on this topic as well if you're interested.

    How to Improve Accuracy W/ High-Speed Comparators in LIDAR and Proximity Sensing (Rev. A) (ti.com)

  • +1
    TI__Guru 68296 points

    Hello Deepak,

    Note that the TLV3801 does not have ground sensing inputs. It's input range is limited to 1.5V above negative and up to VCC.

    You will need to shift the TIA reference so that the input signal swings between 1.5V and whatever you use for VCC.

    Most comparators in the <1ns response time range are going to be some sort of reduced swing differential output (LVDS, PECL, CML), and not push-pull due to having to swing the full supply (3-5V) in 100's of ps. Remember i=C*(dv/dt)?

    As Clemens said, considering the delays added for the LVDS conversions, and the CMOS analog switch cannot be that fast, you may be better off using the TLV3601 (with a full R-R input).