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.
Using the opamp in open loop improves things:
The falling edge when zoomed is still a little bit ugly, but it should be ok:
I wanted to understand further.
IC_Larry said: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.
The configuration works as Comparator.
Your reference is 2.5V.So that is, if your input is 3.3V which is higher than your reference, you got a 5V output.
You might want to consider a comparator in your application.
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.