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

[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]

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?

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

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

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

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?

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

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?

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

Hmmm, this is worrying.  If the current driven out of the LVDS doesn't generate a big enough voltage across the 33 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 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 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]

Hmmm, this is worrying.  If the current driven out of the LVDS doesn't generate a big enough voltage across the 33 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 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 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?

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

[Gandalf_Sr]

thmjpr
Thanks for the commentary. The AUC gates are cool but when I asked on TI's e2e forum about implementing voltage level translation using open drain outputs and pull up resistors, the expert advice was that, although this works, it's very power inefficient and the value of the pullup resistor needs to get smaller as the signals go faster.  They recommended the SN74AXC8T245 which is an 8-bit voltage level translator that uses uAmps and I've got one of these per 8-bit pod.

I will start a new thread soon and link to it from here.

[EDIT] First vn is up in the thread here

[joeyjoejoe]

I think a lower cost pod is a great idea. As a hobbyist the 5000 series scope is at a nice price/feature point, but a LA at 200MHz just isn't needed. My cheap chinese one has been doing fine, so a cheaper pod would also be fine.

[Gandalf_Sr]

My boards are due to arrive today but now I'm starting to worry that the LVDS output of the DS90LV047A will not work properly with the LVPECL input (assuming that is what it is) for the MSO5000 LA interface connector.  The LMH7322 outputs a differential voltage that swings between 0.35 and -0.35 volts  (see first picture) but I've made my DS90LV047A LVDS output circuit drive into a 100 Ohm resistor so my output is not going to centered around zero.  Have I fucked up?

I think I may need to drive into 2 x 50 Ohm with a center offset voltage but it's not clear to me from the DS90LV047A datasheet that this is needed (see second picture).

If this is a mistake I've made, I may be able to make these boards work by putting 2 x 50 Ohm resistors in place of the 100 Ohm one and then feeding a 1.2V supply into the center point of the resistors.

Any comments are welcome.

[Vtech]

It's been a while since I've worked on the probe.

The LMH7322 outputs a differential voltage that swings between 0.35 and -0.35 volts  (see first picture) but I've made my DS90LV047A LVDS output circuit drive into a 100 Ohm resistor so my output is not going to centered around zero.  Have I fucked up?

Why do you think it's zero centered? It's RSPECL. At this VCCO voltage (2.4V) it should output levels H=1.3V, L=0.9V. These should be exactly LVDS levels (common mode voltage around 1.2V).

I can't measure it currently becouse I'm on a leave. I'll be back at work in two weeks.

[Gandalf_Sr]

It's been a while since I've worked on the probe.

The LMH7322 outputs a differential voltage that swings between 0.35 and -0.35 volts  (see first picture) but I've made my DS90LV047A LVDS output circuit drive into a 100 Ohm resistor so my output is not going to centered around zero.  Have I fucked up?

Why do you think it's zero centered? It's RSPECL. At this VCCO voltage (2.4V) it should output levels H=1.3V, L=0.9V. These should be exactly LVDS levels (common mode voltage around 1.2V).

I can't measure it currently becouse I'm on a leave. I'll be back at work in two weeks.

Thanks for the fast response. 

I was looking at the schematic in this post and the driver has +2.4 and -2.4 volts hooked up to it so I was assuming that the output was centered on zero.  Can anyone else confirm whether the voltage on the differential pair is centered on zero or 1.2V?

[EDIT] It does appear that, the way that the real LA probe circuit is connected, the LMH7322 Vcco is set at 2.5V which makes the H/L outputs run at +1.5V/+1.0V which is LVDS-compatible, so I think I'm OK (see picture).

[Gandalf_Sr]

I built one and it works - at 10 MHz in my tests so far.

See these new pictures in my thread.

Thanks for all the support and ideas from this thread.

[EDIT] I have now run my budget probe set at 50 MHz (square wave 3.3V logic levels) and it works as expected but there is an occasional 1nS jitter on the signal.  How does this compare to the real LA probes and the build specified in this thread?

[bigboss59]

So far there is no RPL1116 design ?
(I know it can be easily adapt; I don't want to invent the wheel again)

If not is there anybody have one set of the MSO to sell ? (preferably in Europe)

BR

[koljsch]

Hello!
Someone can tell - after assembling the circuit on the pins, where the voltage should be -2.5 V, the voltage rises to 0.9 V. What is the problem?

[oliv3r]

Here are some photos of RPL1116 Active Logic Probe pod used in MSO1000Z series scope.

Scope has 16 channel logic probe. The probe pod uses 8x LMH7322 (Dual 700ps High Speed Comparator with RSPECL Outputs). 4 comparators on each side. The pod is connected to the scope using 68 pin connector and flat cable. Reference voltage is generated inside the scope.
Cable connector has:
16x2 pins for PECL signals,
22x GND between diff pairs + some extra,
6 pins for VCC
2x2 pins for +/- supply voltage
Some 4 more signals (reference voltage??)


Most likely, the same design is used in new pod for MSO5000 series - PLA2216 Active logic probe. Here are some x-rays of the new pod: https://www.eevblog.com/forum/testgear/hacking-the-rigol-mso5000-series-oscilloscopes/msg2055715/#msg2055715

Vtech, I know we kind of hi-jacked your thread with the MSO5k probe.

I too did a design https://www.eevblog.com/forum/testgear/another-low-cost-la-probe-for-rigol-mso5000-by-oliv3r/ but am really interested if we can port it also to the DS1000Z series. Do you still have one? Would you experiment/help. I'd really need the pinout of course, and while looking at those two pictures, I could get like 33% of the pinout, the other 66% probably needs to be measured. E.g. which pin is what channel, which pins are gnd, which pins are power, and what voltages at that. I know it'll be quite similar to the MSO5k, but still.

[seppeltronics]

Hello,

for the MSO500/PLA2216:

1) Are the schematics and layouts which are a 100% Clone ?
2) Is the circuitry in the genuine big connector and the pod's ?
3) Is there a good clone that is commercially available ?

Thanks a lot.

Best Regards, Seppeltronics.

[Mechatrommer]

Hello,
for the MSO500/PLA2216:
1) Are the schematics and layouts which are a 100% Clone ?
2) Is the circuitry in the genuine big connector and the pod's ?
3) Is there a good clone that is commercially available ?

Thanks a lot.
Best Regards, Seppeltronics.

to answer your PM as well here...

the original circuit and IC teardown and reverse engineering for RPL1116 was made by Vtech...
https://www.eevblog.com/forum/testgear/rpl1116-active-logic-probe-pod-for-1000z-series-teardown/
https://www.eevblog.com/forum/testgear/rpl1116-active-logic-probe-pod-for-1000z-series-teardown/msg2088667/#msg2088667

the pin connector for PLA2216 (please note PLA 2216 and RPL1116 have different pin out into the scope) was described by TopLoser (and maybe others)...
https://www.eevblog.com/forum/testgear/rpl1116-active-logic-probe-pod-for-1000z-series-teardown/msg2086255/#msg2086255

there is no voltage regulator in the pod, you can see from photos here.. Q3: lets hope there will be soon. currently there are few cheap clones based on some driver/logic IC for less than $100, perhaps similar to this...
https://www.eevblog.com/forum/testgear/low-cost-logic-analyzer-probe-for-rigol-mso5000-easyeda-project
https://www.eevblog.com/forum/testgear/another-low-cost-la-probe-for-rigol-mso5000-by-oliv3r

you can follow those useful threads or maybe this thread in case if you want to build your own.  cheers.
https://www.eevblog.com/forum/testgear/low-cost-compatible-rigol-pla2216-logic-probe-for-dho900-(and-hacked-dho800)/msg5352677/#msg5352677
https://www.eevblog.com/forum/testgear/low-cost-compatible-rigol-pla2216-logic-probe-for-dho900-(and-hacked-dho800)/msg5412416/#msg5412416

[seppeltronics]

Hello,

the issue that I have is that these EEVBlog-Forum-Projects contain hundreds of posts and if you do not read them all you might miss information. So I wonder if these are in a git-repo somewhere? Got it: https://gitlab.com/riglol/lapod

I did the calculation, about 60..120€ for the comparators(),... + enclosures, PCB's,... if that is no production-run that is commercially available, it's really hard to do it for less than the original probes?

Best Regards, Seppeltronics