🚀 go-pugleaf

Johnny Boy wrote:
>
> You should listen to David, he knows what he's saying - even the very best
> of rail-to-rail op-amps won't go close to the supply rails, except if
> they're very lightly loaded, 1M etc. They still usually fall short of the
> negative rail by 5-50mV and 0.5-1.5V short of the positive rail.
> ... Johnny

OK, I doublechecked the requirements, I don't have to get the exact
10Vp-p. Maybe I was getting such high output voltages (for OPA657)
because of 1M load


Jamie wrote:
> Vitaliy wrote:
>
> > I've been trying to do that.
> >
> > In a lot of examples on the datasheets of amplifiers I'm looking for, I
> > see they are using 50Ohm input. However, I know for sure (test results)
> > that output of the first stage (photodiode amp) does not work with
> > 50Ohm loads, but works with 1MOhm loads. Should I be concerned about
> > that?
> >
> > Vitaliy
>
>   put an old stand by TL082 type op-amp infront of it.

But that would kill my BW (the BW on that is only 4MHz, and I need
40MHz), right?

redbelly wrote:
> If you're okay with, say 1 usec or slower response time, I wouldn't
> worry about using a 50 ohm load.  You might even be okay with the
> higher impendance at somewhat faster response times, you might need to
> experiment a little.  If you could get by with a 1k or 10k load then
> you'd have an easier time finding an opamp.
>
> You didn't say much yet about the nature of your signal, other than
> it's optical.  Are you looking at light pulses (and at what pulse
> duration), modulated light (and at what frequency), or a more-or-less
> cw signal that changes slowly in intensity (and on what sort of time
> scale does the intensity change)?

I have broadband light source w/ rapid scanning optical delay line
(RSOD) and phase modulator. Are you suggesting this would affect the
required slew rate?

Thanks for all advices,

Vitaliy