AD8397ARDZ as a digital line driver

Hello, I'm using an AD8397ARDZ to make a simple, fast buffer capable to drive 50 ohm loads at 0-5V:

The input is a 0...3.3V HCMOS square wave at 10 kHz.

What I'm experiencing is a "tail" on the falling edge of the output waveform:

I suppose this is due to the common emitter output stage.

Is there a way to improve this behavior, apart from using a dual supply voltage (which I cannot do)?

I've tried to reduce the resistor values (the screenshot actually refers to the configuration R3=R4=220 ohms) but the improvement is quite small.

Thanks!

L.

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    •  Analog Employees 
    on Jul 8, 2020 3:30 AM 6 months ago

    Hi,

    I wanted to understand further.

    loads at 0-5V:

    Since your output is a square wave, is the 0 - 5V here is a logic level?
    0V for Logic Lo and 5V for Logic Hi?
    If yes, what is your acceptable range for Logic Lo and acceptable range for Logic Hi?

    Also, are you limited to 5V single supply or you can go beyond? Say 10V single supply.

    Thanks and regards.

  • Hi Fdelaram, sorry for the delay but i didn't receive a notification on your reply. Of course a comparator would be a cleaner choice, but it seems quite difficult to find one capable to drive 50 ohm loads.

    The circuit will drive the enable input of a pulsed LASER driver. The specifications are quite fuzzy, we don't know the actual input voltage threshold and therefore we need to stick as close as possible to the 0-5V levels.

    Anyway, in the meantime we actually have tested the circuit and it seems to work fine. The LASER fires on the rising edge, and the uglinesses on the falling edge don't seem to trigger false firings.

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  • Hi Fdelaram, sorry for the delay but i didn't receive a notification on your reply. Of course a comparator would be a cleaner choice, but it seems quite difficult to find one capable to drive 50 ohm loads.

    The circuit will drive the enable input of a pulsed LASER driver. The specifications are quite fuzzy, we don't know the actual input voltage threshold and therefore we need to stick as close as possible to the 0-5V levels.

    Anyway, in the meantime we actually have tested the circuit and it seems to work fine. The LASER fires on the rising edge, and the uglinesses on the falling edge don't seem to trigger false firings.

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