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

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Gandalf_Sr:
I've ordered my MSO5074 - without the PLA2216 because I refuse to pay 36% of the cost of the whole scope for a couple of ICs, a bit of cable, and the clip thingies.  I looked at the good work done here to reverse engineer the PLA2216 but the end result seems too complicated and expensive - mainly because it seems to emulate a probe that might be used on very high frequencies; much higher than the 200 MHz that the LA inputs are rated for on the MSO5000.

So I plan to design and build a simpler, lower frequency probe that uses cheaper DS90LV047A LVDS drivers and a simple 74AUCxxx front end buffer with open drain outputs that will allow it to perform voltage level translation using a single resistor per channel.  The 74AUC family is newish and has very low propagation delays of around 2 nS. I will post a new thread for this which I will come back and link from here but I do have a couple of questions that I hope you guys can answer that will speed me on my mission:

1. Regarding the 1/10 reference voltages that the MSO5000 puts out:
    a. Is this as straightforward as it sounds? For 3.3V logic the scope outputs 0.33V etc?
    b. How many different voltages are selectable from the scope's menu?
2. The LVDS buffer IC I'm considering shows that the output is done by sending current out of the +/- output pair and requires a 90 - 130\$\Omega\$ termination resistor across the output to generate the +/- voltage signal.  My driver IC will run at 3.3 volts and my question is - is the termination resistor required or are resistors already there internal to the MSO5000 LA input?
3. I plan to use a controllable Vcc to the 74AUCxxx buffer to adapt to the input voltage selected - this is going to be a microcontroller which I'm well able to do but I would prefer a simpler solution - any thoughts or ideas?

Thanks in advance.

ebclr:
Interesting Idea, Keep us informed on the development

thmjpr:

--- Quote from: Gandalf_Sr on February 20, 2020, 10:42:30 am ---1. Regarding the 1/10 reference voltages that the MSO5000 puts out:
    a. Is this as straightforward as it sounds? For 3.3V logic the scope outputs 0.33V etc?

--- End quote ---

Yeah, its commented in my code somewhere. Roughly -1.5 to +1.5V


--- Quote ---    b. How many different voltages are selectable from the scope's menu?

--- End quote ---

-15V to 15V in 10mV steps if I remember correctly.


--- Quote ---2. The LVDS buffer IC I'm considering shows that the output is done by sending current out of the +/- output pair and requires a 90 - 130\$\Omega\$ termination resistor across the output to generate the +/- voltage signal.  My driver IC will run at 3.3 volts and my question is - is the termination resistor required or are resistors already there internal to the MSO5000 LA input?

--- End quote ---

It looks like there are 33 ohm series resistors. I don't think there is any internal parallel termination, but I can measure it later.
https://gitlab.com/riglol/rigolee/-/wikis/MSO5000-teardown

Gandalf_Sr:
Thanks so much for the information

--- Quote from: thmjpr on February 21, 2020, 12:26:49 am ---
--- Quote from: Gandalf_Sr on February 20, 2020, 10:42:30 am ---2. The LVDS buffer IC I'm considering shows that the output is done by sending current out of the +/- output pair and requires a 90 - 130\$\Omega\$ termination resistor across the output to generate the +/- voltage signal.  My driver IC will run at 3.3 volts and my question is - is the termination resistor required or are resistors already there internal to the MSO5000 LA input?

--- End quote ---

It looks like there are 33 ohm series resistors. I don't think there is any internal parallel termination, but I can measure it later.
https://gitlab.com/riglol/rigolee/-/wikis/MSO5000-teardown


--- End quote ---
Hmmm, this is worrying.  If the current driven out of the LVDS doesn't generate a big enough voltage across the 33 \$\Omega\$ resistor then my whole approach isn't going to work without changing the internal resistors which I'm not going to do.  I think the only thing to do is to get an LVDS IC (I'm planning on the DS90LV047A) and try it from a breadboard to make sure it triggers the level changes accurately.  It puts out a nominal 20 mA which, if driven across a 33 \$\Omega\$ resistor, would give 0.66 Volts across whatever IC is receiving the signal.  I looked at the GIThub tear down but couldn't see what that might be?

[EDIT] Oh, you said SERIES resistor so maybe if I include 100 \$\Omega\$ parallel resistors just before the connector, they will feed through to the MSO5000 and work properly? Will need to test.

I have created the 50 pin connector component in Diptrace and the screen capture of it is below.  Can anyone confirm what pin 10 is and whether the other pins are correct, particularly the Ps and Ns?

thmjpr:

--- Quote from: Gandalf_Sr on February 22, 2020, 12:39:12 pm ---Hmmm, this is worrying.  If the current driven out of the LVDS doesn't generate a big enough voltage across the 33 \$\Omega\$ resistor then my whole approach isn't going to work without changing the internal resistors which I'm not going to do.  I think the only thing to do is to get an LVDS IC (I'm planning on the DS90LV047A) and try it from a breadboard to make sure it triggers the level changes accurately.  It puts out a nominal 20 mA which, if driven across a 33 \$\Omega\$ resistor, would give 0.66 Volts across whatever IC is receiving the signal.  I looked at the GIThub tear down but couldn't see what that might be?

[EDIT] Oh, you said SERIES resistor so maybe if I include 100 \$\Omega\$ parallel resistors just before the connector, they will feed through to the MSO5000 and work properly? Will need to test.

I have created the 50 pin connector component in Diptrace and the screen capture of it is below.  Can anyone confirm what pin 10 is and whether the other pins are correct, particularly the Ps and Ns?

--- End quote ---

Series resistors, yeah. In the teardown photos they go through the resistor pack, a via, then disappear to an inner layer. I can't measure any relevant sort of parallel resistance on the connector itself, its ~1M. So probably goes straight into some ICs input pins.
Connector pinout looks correct.

I don't even know if parallel resistors would be needed on your board? Unless you had them for signal integrity purposes. No harm in adding a footprint for them though.

The 74AUC gates look cool https://hackaday.io/project/28833-microhacks/log/157535-just-how-fast-are-74auc-gates

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