Hi Welcome to the Eev blog an Electronics Engineering Video blog of interest to anyone involved in electronics design. I'm your host Dave Jones Hi In the previous blog, I reviewed the new Agilant 2000x series oscilloscope and it was a beauty and I did a tear down of it which everyone seemed to love but I forgot one thing I forgot to tear down the optional Lan VGA module and somebody asked if I could do it. Is there any circuitry inside here are ageline just ripping you off? Is it just the connectors and all the circuitry is still inside the scope? Well what do you get for your 400 bucks? Good question. Let's find out somehow: I don't think I need to do this in uh, fast motion.

There's only two screws on it by the looks of it, so let's crack it open. There's one and there's the other I can see circuitry in there? Look at that. Tada Wa whoa hello Tada look at it. There we go.

They're not ripping you off. There is some circuitry in there. Okay, let's take a look at what we got here. We've got a Spartan uh 3s1, 100 Fpga on the top here, which is not a particularly uh top of line FP PGA It's a rather, uh, cheap one.

it's only 100K Gates And on the back here we've got a 4 mbit Cypress uh SRAM which is obviously the Uh frame buffer for the VGA output coupled with the Fpga on the top. The Fpga does all the timing and everything else and uh, the actual Uh Frame data for the VGA display is stored in the 4 Mbit SRAM there and down here. we've got an Analog Devices uh, Advv 7125 and that there is a three Channel Dack Very typical of what you'd find in a VGA uh typical VGA display. So this is a classic uh Fpga implemented uh VGA display these these two devices here.

obviously uh, voltage, local voltage regulation. You can tell by the power tracks actually going to them and the input and output capacitors. it's a dead giveaway. I don't even have to read the numbers on those to figure it out.

And and one thing you'll notice is that there is no Um circuitry for the Landan at all. All we've got is the two differential pairs coming out here going straight into the connector. and this is just a classic uh, what they call a MAG Jack um or a magnetic Jack because it contains the magnetics required for Um for isolation for the ethernet Uh interface. So not only will that magjack contain the Uh the isolation Transformers it'll also contain the termination resistors as well.

cuz normally uh, these used to be separate devices. You used to have to have separate isolation. Transformers If you seen like an old uh PC um Ethernet card then you'll see these little big black uh Square uh isolation Transformers Well, they don't have those anymore. Pretty much everyone is using these uh Mag Jacks that they really are the way to go.

So clearly the Ethernet interface is being handled by the Arm uh Micro. These these differential pairs. Here they'll be matched length. Of course they will go straight into Um straight into the Arm 9 Uh Micro which we saw in the Uh in the tear down of the scope.

So and there's a JTAG interface over here of course for the Uh for the Um Fpga and that's pretty much it. There's nothing you know. it's just a basic Um implemented Uh VGA controller. With the Uh Dack for the RGB signals, it generates the timing.

One thing you'll notice that's not on here is a crystal. There is no Uh oscillator at all on here, so obviously the timing is coming from uh, the main board. It's coming from the DSO so that's where it gets its clock from. I Guess why not? Because you save a bit of system cost there.

Why would you bother putting a uh, an oscillator on here which you know might cost 50 cents or something When you can, uh, tap the signal straight from your DSO along here. so they're up to rev six on the board. I Think that was uh, the same as what was in the DSO from memory. So they've had six goes at this board either.

Well, A Either they've had six goes at it or B they actually, uh, automatically update this board when the other one gets updated. That's a another technique, but I doubt it. Um, it' be a bit silly to update this particular module. It would be its own project and well, there's not much in here at all.

so it's certainly not 400 bucks worth of Parts It's you know, even from Digi ke one off, it's probably only uh, 30 or 40 bucks worth of parts. so it's not much at all. So clearly, uh, what you're paying for is the Uh development and you're paying for Well, because it's Agilant where everything's optional extra. let's take a quick look at the layout because there's something I immediately noticed here: the Dack Okay, the entire Dack Uh subsystem here is.

well, it's here. and why isn't it up near the VGA connector? Because if I was laying out this board, I would have gone right. I've got a deck that has, um, analog output signals and it should be near its connector. The last thing you want is for those signals to be running right across the board and especially you don't want them running underneath a a highspeed SRAM Like that with all those digital signals blaring away you? really? that's the last thing you want.

So I reckon it's a very strange layout decision there. I Mean they. they've obviously got a six layer board here. The reason you can tell that is because there's virtually no tracks coming out of this.

Uh, SRAM here. they're just going down into some Vs down there and if you have a look on the top, there's no corresponding tracks on the top which go to the Fpga So obviously they're on internal layers. so you would have uh, two internal signal layers. Plus, you can see that there's uh, ground and there's likely a power um, plane in there as well.

So that is likely a Uh six layer board. So well, it's a minimum of a six layer board because you can't see the inner traces on the bottom. So that's how you can tell um, that there's a ground and a power. Um, so like layers, you know two and five would be ground and power and with the two signal layers in the middle which you can't see now? Yeah, I Just think that's a crazy decision.

and the other thing you'll notice is that it's a two-sided load. There's components on both sides and that just increases your manufacturing cost and complexity. Now granted, I don't know how many modules of these, how many of these modules they're actually going to sell. So the point might be a bit mood.

But as as a layout designer, I would have tried to get this as a first pass. I would have tried to lay this out all on one side. here. You know you could have moved the Uh Fpga down to the bottom here.

You could have put the SRAM right next to it or above it or something like that. You could have put the Dack and all of its Associated Uh, circuitry up near the connector here. So you might have had Fpga here SRAM sort of tucked in there Dack over in this corner here and your power supplies. you know here or something like that because you've got your ground planes there and they're low inductance? You don't necessarily.

um, need your uh Power Supplies right next to the Fpga You've got a bit of leeway there, but uh, granted, you wouldn't. actually. on second thought, you wouldn't put say this regulator over here because then these are the two input uh, Power tracks. You've got to get those over there.

which is crazy. So I would have. Yeah, I would have just moved that down to there. put it in there.

put the well on on the top side. Anyway, this one would have gone down in this corner over here. and then the Fpga Yep, tucks in, tucks in the middle there. SRAM Boom I Don't know.

I I Just found that layout decision strange. I Don't know what the layout designer was thinking. So why have they gone and put the Lan and the VGA on a separate plug-in module? Why didn't they build it into the scope? Well, your guess is as good as mine, but uh, it obviously has a lot to do with. Um, it all ties into the system engineering aspect of it.

The uh. budget constraints for the scope because when when you're designing a base model scope like this one, you really do have to be uh, cost conscious. And although these parts on here aren't worth an absolute Uh Fortune, they do eat into your Uh budget your Um Bill of Materials budget for your scope. So really, you know the VGA side of it I can kind of understand why they sort of separated this out.

Now you could argue that the Arm 9 processor in the Uh DSO because it's not actually handling the refresh of the screen directly. which is what we found out in the previous blog when we did the tear down. Um, it's handled by the Asic in there. so maybe it would have had some grunt left over to do the VGA direct, but then you still would have needed the frame buffer and you know everything else and well.

you know you're going to need this external circuitry and you're probably going to need the Dack uh as well because I don't think that the Um Arm chip has a built-in VGA output I haven't checked, but I'm assuming that it doesn't. So really, from a a systems engineering point of view, it kind of makes sense to separate out the VGA so they could have done this as just a video output board. Now why they've chosen VGA VGA is a legacy interface. Really? it's um, it really is dying out.

It would have been a much more sensible choice to do a HDMI DVI interface. Um, you know, for 400 Buck module, he could have easily afforded to do a uh a HDMI output version. So I don't know why they've done that. Now when it comes to the Landan interface, the only component they're saving cost on in the DSO is the magjack and Mag jaacks Aren't that expensive at all.

They're very, very cheap. So why Agilant have not included this in the base model? DSO I It's not a bill of materials. Uh issue. It's not a cost issue.

It would have been a Uh marketing issue. It would have been like Marketing sales they wanted. Maybe they thought, oh, if we just had this as a video board then, well, maybe they made the decision first. Okay, let's separate out this video board.

You know we can't really afford the cost in the base uh unit, Fair enough. Let's put on a separate ball boot. Hey And then somebody said, hey, we can't afford. You know, we can't just have a video output board.

People aren't going to buy just that. So why not put separate out something that's more useful to make it entice in to buy this module. Why not stick the land on there? Everyone's going to want a land they think they're getting real value for money. If we just charge 400 bucks for just the VGA interface, people might get a bit pissed off.

Maybe, But uh, you know. So why not SE out the land? So maybe that's where the designed decision for separating out the land come from I Don't know. Pure utter speculation on my part, but an educated guess.