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TLV3801: 0mV and split power supply comparator option

Shine Jo Tom
Prodigy 120 points
Part Number: TLV3801
Other Parts Discussed in Thread: TLV1871, TLV3811

Tool/software:

Hi Team,

I have been so far using the TLV3801 comparator for my project. But I now require a comparators with the following criteria; 0mV hysteresis and input split power supply. TLV3811C looks to be a great candidate but it doesn't have an input split power supply. The idea is that I need to compare a 500MHz high-speed ac-coupled signal with 0V/ground. Could you propose any components/ circuits that could be useful for this?

  • 0
    Guru 284090 points

    As far as I know, the only other comparator with split supplies is the TLV1871, which is too slow.

    If the input is AC-coupled, couldn't you bias the TLV3811‍C's input voltage higher?

  • 0 in reply to Clemens Ladisch
    Prodigy 120 points

    Thanks for your prompt reply.

    May I know if you could suggest an optimal way of biasing the high-speed signal using just passive components without affecting the speed at all? I don't want to use any additional FDA or other IC components for the same. On an additional note, I have a very low noise LDO of 2V which can be used as the bias voltage.

  • 0 in reply to Shine Jo Tom
    Guru 284090 points

    Typically, you'd use a resistor divider with a voltage in the middle of the common-mode voltage range.

    Do you have any requirements for termination impedance?

  • 0 in reply to Clemens Ladisch
    Prodigy 120 points

    Hi,

    Yes, the ac-coupled output of MAX40660 https://www.analog.com/media/en/technical-documentation/data-sheets/MAX40660-MAX40661.pdf (image below) needs to be compared with the voltage of 2V from a LDO (since it's ground is not possible).

    Only one of the differential pair of MAX40660 would be used, let's say OUTP and the other OUTN would be terminated with 50ohms to ground after the ac-coupling capacitor. Both traces will be routed as single-ended co-planar traces.

    To maintain signal integrity and avoid reflections, I believe 50ohms termination is required after the 0.1uF coupling capacitor. Is it possible to just use a pull-up resistor with 50ohms to 2V for ac-coupled the signal output to be connected to the input (non-inverting input) of the TLV3811C's? The other input (let's say inverting input) of the comparator can also be pulled-up to 2V with 50ohms Would this be enough or do we need any other circuit?

    The single-supply voltage can be around 3.3V and the maximum peak-to-peak output signal of MAX40660 is around +-150mV with respect to ground.

  • 0 in reply to Shine Jo Tom
    Guru 284090 points

    A single pull-up or -down resistor has the correct impedance. (This is called parallel termination.)

    But you would not need the 2 V supply with Thevenin termination, i.e., a resistor divider (whose impedance can be computed as the two resistors in parallel).

    As far as I can see, the MAX40660 datasheet does not guarantee a fixed output common-mode voltage, so it might be necessary to create a proper differential receiver.

  • 0 in reply to Shine Jo Tom
    TI__Expert 5985 points

    Hi Shine,

    Could you please provide a block diagram of what you're trying to achieve? In addition, why is a comparator with separate supplies necessary for your application?

    Thanks,

    Ho