Analog Devices eval board layout wtfs - Page 1
Forum section: electronics / general

author: c4757p
author_rank: Super Contributor
timestamp: February 16, 2015, 06:47:44 am
content: What is up with the bizarre layout on these ADI DDS eval boards?

author: Howardlong
author_rank: Super Contributor
timestamp: February 16, 2015, 07:48:34 am
content: Looks like they are trying to maintain minimum phase difference between DAC channels.What's not so good is the proximity of the SMA connectors, particularly around the SYNC area, it will make it interesting trying to screw in adjacent plugs.

author: tautech
author_rank: Super Contributor
timestamp: February 16, 2015, 08:29:38 am
content: Are you sure the PCB layout image matches the PCB photo?

author: c4757p
author_rank: Super Contributor
timestamp: February 16, 2015, 03:42:48 pm
content: Quote from: Howardlong on February 16, 2015, 07:48:34 amYeah, that I see. Look at the rest of it though, like the low-speed digital section. All those sharp corners and whatnot - not muchwrongwith it, but it just looksweirdWhoever did thesedoesappear to have known what he was doing, but added a good does of layout chaos just because... It feels rather like a conscious style decision!Quote from: tautech on February 16, 2015, 08:29:38 amTwo different PCBs. I couldn't get a proper layout image for the one in the photo - they have the Gerbers available for download, but the format of them is funny and nothing I have would touch them.

author: iampoor
author_rank: Frequent Contributor
timestamp: February 16, 2015, 08:21:57 pm
content: Looks like the a city planner who took up PCB layout did it.

author: c4757p
author_rank: Super Contributor
timestamp: February 16, 2015, 09:42:41 pm
content: Quote from: Howardlong on February 16, 2015, 07:48:34 amBack to this - if I remember correctly (I'm currently using this chip but I did the layout months ago) you're rather unlikely to use all three of those at once. Either SYNC_IN or SYNC_OUT (or in most cases, neither - that's one bleeding expensive chip and I'm not sure how many applications would need master/slave pairs of them).It's still a bit cramped with even two, but it's not quite as bad as with three, as most SMA plugs have some play and the one next to the one you're fiddling with can shift outward a bit if there's no third plug to block it.The SMA configurationissilly though. Somanyof them! Why the hell do they have a whole bunch of them on the AVDD bus!? Not even brought right up to the pins (maybe to measure ripple as this thing hums along at 500 MHz) but right next to caps. Forprovidingpower, maybe? Why would you use SMA for power input?Some of them are funnier too, like the one labeled "Band Gap Supply" when the datasheet mentions absolutely nothing about a bandgap anything. Presumably based on some internal knowledge of what's powered by which pins - the datasheet just lists AVDD, DVDD and DVDD_I/O...

author: Neganur
author_rank: Unknown
timestamp: February 16, 2015, 10:58:39 pm
content: everything is matched to length, and I agree they are too crammed. It's a pain in the arse to get in there with fat fingers.The outputs are complementary current steering (you can set the current of each output iirc, binary attenuation), then you can choose with or without filter.Almost wonder why they don't also provide for a differential ref clk inputBut AD eval boards are really nice otherwise

author: c4757p
author_rank: Super Contributor
timestamp: February 16, 2015, 11:12:15 pm
content: Full-scale current is set for all outputs at once, using a reference resistor; you can attenuate the differential signals digitally.As for the ref clk, I get the feeling that the clocking is in a completely different part of the chip, where they've got the crystal oscillator and PLL and whatnot. Not too sure about the internal architecture of it all though.Quote from: Neganur on February 16, 2015, 10:58:39 pmI don't think I've everhadan ADI eval board - bit expensive for me! - but all their stuff in general has always seemed nice to me

author: free_electron
author_rank: Super Contributor
timestamp: February 18, 2015, 08:22:10 pm
content: designed for signal time-of-flight. ( phase shift )nothing special. I had to do that all the time when doing harddisk preamps.

author: c4757p
author_rank: Super Contributor
timestamp: February 19, 2015, 01:54:30 pm
content: Quote from: free_electron on February 18, 2015, 08:22:10 pmAddressed that already