Products > Test Equipment

RPL1116 (MSO1000Z) and PLA2216 (MSO5000) Active Logic Probe teardown

<< < (45/50) > >>

MarkL:

--- Quote from: Gandalf_Sr on February 15, 2020, 03:56:20 pm ---...
So I'm considering a poor man's logic probe that would be good for up to 100 MHz ish, I realize low propagation delay may be a necessity for digital timing alongside the analog signals but some logic families such as TI's AUC go down to 1.5 nS propagation delay although I think that the MSO5000 needs +/- LVDS signals.
...

--- End quote ---
Just a comment on the propagation delay...

If you're concerned about matching the analog channel delay to a home-brew digital probe delay, the Rigol 5000 has a channel delay adjustment.  It's not clear from the user manual if you can adjust the digital channels, but you can certainly move the analog channels relative to the digital.  And although it doesn't say, I'm a sure a few nanoseconds would be within its range.

Most scopes have this, even old analog scopes.  Also known as channel-to-channel skew adjustment.

Gandalf_Sr:
OK, here is the simplest form I can imagine for my design idea:

1 There could be 4 x DS90LV047A converting single-ended 3.3V CMOS logic levels into LVDS differential signals.  Cost about $11
2. A single 74AUC16244 acting as a 16 bit buffer and voltage level translator following the advice in the TI little logic guide starting on page 19.

The AUC device at 2 above could be multiple devices e.g. 4 x 4bit buffer.

The different voltage levels being sensed could be handled by different Vcc values used for the AUC buffer.  How did the original design do this and was there some sort of setting in the MSO5000 to define what was being sensed?

If the DS90LV047A devices convert single ended into LVDS signals then I think it makes more sense to have them on the smaller PCBs close to the point of sensing and then send LVDS signals over the ribbon cable to the board that plugs into the MSO5000.

What about the input protection circuitry?

Comments please.

Gandalf_Sr:
OK, to self-comment.  I've been looking for comparators that would be a front end for the DS90LV047A but they are either too slow or too expensive so the LMH7324 seems like a good option and, at 700 pS propagation delay, it's the fastest that TI has listed.  However, the minimum Vcc is supposed to be 5V, was that catered for in the designs you guys have implemented?

TopLoser:
There's only a maximum of 4V supply available on the scope connector.

Start reading the thread from the beginning, it's got answers to lots of your questions.

Gandalf_Sr:

--- Quote from: TopLoser on February 16, 2020, 04:06:58 pm ---There's only a maximum of 4V supply available on the scope connector.

Start reading the thread from the beginning, it's got answers to lots of your questions.

--- End quote ---
I've read the whole thread a couple of times.  I saw the comment that the comparator only had 4V and needed 5.  Someone responded that there was a -2.1V available on the scope connector which could be added to the +4V, so in the designs, does the comparator run on 4V or more?

Maybe it runs OK at 4V?

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod