TTL signal

What sort of TTL are you going to use with a 3 ns pulse????

Cheers,

Phil Hobbs

One that stays solidly at either a high or low level?

Bob

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I'm looking to use the TTL as a trigger pulse for an NI scope application. So the pulse can be stretched longer than the 3nS pulse. The 3-5nS pulse is coming from a photodiode circuit on a Cobolt Tango Laser.

=3D

It does not have to stay high or low, except sufficiently to be used as a trigger for NI scope input.

Sno-o-o-o-o-ort ;-)

...Jim Thompson

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LVDS receivers make nice comparators with "CMOS"/"TTL" outputs at these input voltage levels.

e.g. DS90C032 et al for few hundred mV swing inputs.

If the input isn't actually differential then appropriately biasing the inactive input does the trick.

Sometimes the same parts used to be known as LVPECL receivers.

Tim.

That's a bit on the fast side for a TTL-level output, but you can try looking at fast comparators. LVDS (or PECL or CML) will be easier.

You should probably think in terms that the pulse _must be_ stretched, not "could be". Check the documentation on your hardware.

I assume that you're looking for a circuit? Your question didn't make it clear.

Perhaps you should start over again and tell the _whole_ story: "I am trying to trigger a NI scope board (which one?) with a Cobolt Tango laser which has a photodiode output. The NI board needs a TTL-level input, but the laser pulse is 3-5ns long and only 150mV high". Something like that.

Then you'll have provided a much nicer framework for folks to answer your need.

You may want to make clear your requirements for jitter and maximum pulse width -- if you have to slow it down for TTL you can pretty much guarantee that you'll introduce jitter in the process, or the receiving board will.

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

Uh, really, really, really fast TTL?

I assume the scope has an analog trigger input, with programmable trigger level. So maybe all you need is a linear amplifier.

Like this, maybe:

This is likly a single MMIC in a can, so probably inverts the signal.

If the scope really needs TTL, of course we could sell you one of these...

John

You have not specified if there is a DC component in this signal?

It would make a world of difference in design to know this.

From what I can gather in your info, it's 0..150v but it may actually be a 10 to 10.150V PK, for example. etc..

"

The one in the textbook?

Cheers! Rich

Googlies don't know how to do that. If they did, they'd get their own answers. This is just copied out of the exam.

Cheers! Rich

Upside-down ECL? ;-)

Cheers! Rich

I like the left handed one's my self!

"

Maybe he should go back and use gold enhanced RTL logic??

I worked up a pulse-stretcher for pretty much exactly this application

Ghiggino, K.P., Phillips, D., and Sloman, A.W. "Nanosecond pulse stretcher",Journal of Physics E: Scientific Instruments, 12, 686-687 (1979).

It used a pair of 5GHZ wideband transistors to make a Schmitt trigger

- these days I'd probably use BFR92 npn parts rather than the pnp parts we used back then.

It worked. It could have been improved, but since it did the job nobody was interested in going to the trouble of designing something better.

-- Bill Sloman, Nijmegen

Hey, it works!

ftp://66.117.156.8/3ns_TTL.jpg

That's a 3 ns, 100 mV input and 4 volts out. It even works with an 80 mV, 1 ns input, still 4 volts out. I'm sort of impressed!

John

I just built one of those amps into a 6 GHz microwave setup yesterday.

16 dB gain at 1 GHz, 12 dB at 6 GHz, $50 with nice gold-plated SMA connectors. Not bad.

BTW John, could you set up your FTP server to accept PASV? I have to download those pictures using command-line FTP and look at them in a photo editor, because Mozilla browsers always want to use passive-mode FTP.

Cheers,

Phil Hobbs