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A question about effect of external trigger to the risetime a driver output


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Dec 5, 2019
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A laser driver outputs very short pulses with very fast rise times required for some laser diode applications. But the driver requires an external trigger to operate. I want to give an example scenario to make my question clear, and expecting an estimate approximate answer.

Here is the manual pdf.

The manual states that the driver output's rise/fall times as 100ps.

My confusion is, will the external trigger source I will use affect the driver's output rise time or it will only affect the jitter?

Figure 1 in that manual, it looks like a Schmitt trigger on the trigger input (0.5 V). The manual says the device can provide 250 picosecond pulse width.

But I need an external trigger source for this device. And if I use a microcontroller PWM the rising edge of my external trigger can be up to 100ns. If by using an external trigger device I provide 1MHz pulse train with 100ns rise time(fx. from a microcontroller) to this driver, will the driver output's rise/fall time affected? Basically I'm asking whether my external trigger rise time will affect the device output's rise-time.

(I hope my question is clear enough and I'm satisfied with some approximate answer since I cannot provide more details at the moment.)
A very slow risetime may affect the driver. Any risetime
greater than the driver prop delay should be suspect,
and tested.

In addition to slowness you might see "multi-pulsing"
if the risetime is slow enough that ground bounce can
"wrap back around to the input" before the output moves
appreciably (as with very strong predrivers and high
internal loading, to create a leading ground impulse
before the output stage swings, perhaps causing the
front end to "dither" until the input has passed the logic
threshold plus any in-the-moment ground perturbation).

PWM resource risetimes probably are sandbagged for
external loading, and timing is probably quite "notchy"
when you get to the narrow pulse width end. You might
prefer to use a fast one-shot and a regular logic resource,
and get your pulse control some other way than a PWM
register and perhaps-too-leisurely PWM output buffer
(if that's different than a logic I/O).

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