Richard Ottosen wrote:
>
> With respect to risetime verses bandwidth:
> An approximation is Risetime = 1/Frequency * 0.35.
> This gives 70MHz bandwidth for a 5ns risetime. Not trivial but a lot
> easier than 280MHz. There are a lot of voltage and current feedback
> opamps available for these frequencies and risetimes. Not terribly
> expensive either.
>


Thanks- I guess I did remember the equation wrong.  This also brings the
frequency well within what I would expect from some fast TTL... now the
big question is, how do I modulate the LED and recieve it that fast?  I
remember reading in a scope manual about how two consecutive rise times
affect each other- something like a 10ns rise time into an amplifier
with a 10ns rise time gives about a 14ns rise time? (I seem to remember
a sqrt(2) in there).  I guess the LED needs about a 100MHz BW from the
LED to get the 5ns rise time out of a 70MHz reciever.

So, how about it... anyone have circuits for transmitting/recieving
light modulated at about 100MHz?  Gigabit Ethernet does it at over 1GHz,
and OC192 approaches 10 GHz optically, so there should be a way.

Matt

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body