Simulating a monostable

[alec_t]

It's easy enough to model monostable action using e.g. a CD4000 series monostable model, or logic gate models etc, but these all involve external R and C.
Is it possible to use just a behavioral (or standard) voltage source instead, with trigger instant and period both set by parameters? I've faffed around with a bvs but can't come up with a suitable formula to get from it, for example, a voltage which goes low for a period T in response to the falling edge of some other signal.

 

[MikeMl]

Are you using LTSpice? If so, read the help file on the Behavioral Source, specifically the function:absdelay(x,t[,tmax]) x delayed by t.

 

[alec_t]

Yes, LTSpice (sorry; thought everyone here was using LTSpice ). Read that. That's what I was faffing with. It just delays an input waveform rather than start a pulse in response to a falling edge of the waveform. So no joy so far. Maybe that function can be tweaked, but I haven't yet found how. But thanks anyway MikeMl.

 

[kubeek]

Well if you combine that with an RS latch, you might get what you wanted.
Remember that this is how a 555 monostable works. Also you might want the latch with priority on one of the inputs in case there is a long control impulse.

 

[alec_t]

Thanks, kubeek. That gives me another way to cobble together something. I was hoping to avoid multiple devices and to use only a single LTS parameterised voltage source. Looks like that's not going to be doable.

 

[Roff]

Post deleted.

 

[Roff]

Here's a start (unless you've already been this far already). Note that the input pulse must be wider than the output (param PW). I know that's not good, but it's as far as I got.
Also, I see no way to control output transition times in a B element.

Note that the input pulse amplitude may be anything (I think it has to be constant (flat). The output will swing between 0V and Vhigh.

 

[alec_t]

it's as far as I got

...and further than I got.
That looks handy in many situations. Thanks Roff.