Hi - I'm not sure if this is something that exists or not, but I feel like I should ask anyways. I'm working on building the sensor cables for a open source/open hardware logic analyzer
Thanks!
-Mike
You're welcome!
I'm seeing the word "buffer" but thinking "comparitor". Something like the nice LMH7220 could be OK. At a push maybe the LMV7219. Looks like the easy bit is done. The headscratching comes with interfacing to the real world. :) john
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Thinking "comparator" generates nearly a hundred times more hits on Google (67,900 versus 6,120,000).
100MHz would be pushing it for regular comparators with TTL-compatible outputs, while fast comparators with ECL-compatible outputs can pretty much all make 100MHz or better - the orgininal Am685 could just do 100MHz and its many sucessors are all faster.The balanced ECL-compatible outputs are very much easier to keep out of the sensitive fast inputs on these beasts than the TTL outputs you can get away with on slower comparators, so they shouldn't be seen as a bug but rather a feature.
As John Larkin is shortly going to point out, ECL line-receivers and LVDS receivers are very fast, relatively low-gain comparators, available in multi-comparator packages intended to hang on the ends of relatively wide buses.
Here is a data sheet for a dual part
John actually uses the parts (as opposed to reading the data sheets and longing for a chance to use them) and will come up with more part nmbers.
-- Bill Sloman, Nijmegen (but in Sydney at the moment).
Indeed, this is true. 2 much reading of these damned newsgroups is imprinting me. Anyway, I'd have thought the LMH7220 would be ideal in this job. A simple to use, true compar-a-tor with LVDS out, allowing a decent length of twisted pair from the test pod. (So nifty I had to buy a sampling scope to confirm the speed) john
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Hi Bill - thanks for the help. One question though: Are there any parts with more channels that can operate at these speeds? I was thinking that they'd be a fairly common item - but so far I can't find any that can achieve speeds like that. Thanks,
-Mike
My venerable (1965) MC1650/51 comparator design has a 3.5ns tpd (typ).
You can still buy it, 41 years after I designed it, from Lansdale...
Motorola built a 32-wide version for WPAFB, but it was never commercially available.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
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| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
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I love to cook with wine. Sometimes I even put it in the food.
A quick serach of the National website found me two quad line receivers
If you need the gain of a real comparator, you really are restrcted to parts with balanced ECL-compatible outputs and they come in single parts and duals. The Am687 comes to mind.
Jim Thompsons MC1650/1 is, of course, older, but the latching arrangement isn't as nice as the one on the AM685/687, which is why I've never used it and probably explains why everybody else has second-sourced and improved the Am parts.
I've also used the Analog Devices AD9685
Analog has faster comparators
but you probably don't need that much speed.
-- Bill Sloman, Nijmegen (but in Sydney at the moment).
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