Electronics > Projects, Designs, and Technical Stuff
decent but affordable 16 bit DAC
OM222O:
--- Quote from: nemail2 on June 13, 2019, 08:04:34 am ---when crossing traces, I tried to only do it in 90 degrees and I tried to separate digital and analog stuff as much as possible and I tried to keep traces as short as possible, especially for the critical (analog) parts.
So.. I thought it was halfway decent but appearently not :-DD so I'll gladly take any advice on how to optimize the layout. I don't really know what to optimize there, apart from relayouting everything. However if I'd do that, it might end up worse than it is now. Or quite the same :-DD
--- End quote ---
I can see your point about the traces being 90 degrees to each other, but that's not how it works :-DD it's never that simple in electronics :scared:
It has more to do with loop area, rather than overlap of the traces themselves, although this will reduce the coupled noise, it's not as effective as you think :-//
I will do some layout examples on how to properly segment the board into blocks and how to separate the signals / grounds properly.
OM222O:
here is a very basic schematic and layout, just to get the point across (didn't spend too much time on cleanliness, but it's still not too shabby):
https://easyeda.com/theepicn008/layout-example
Thinks to note:
* I didn't use a proper MCU breakout board. just 2 4-pin headers as an approximation. use the proper teensy breakout pins
* I went with a linear regulator since it was easier to draw than the switch mode one you have. again this isn't a major point here
* VCC is a thick track running at the bottom. this is the voltage input to everything
as you can see, the digital and analog traces are completely seperate: digital stuff on the left and analog stuff on the right. if you draw a line in the middle of the board, you can see the DAC and ADC both have the digital IO on one half, and the analog IO on the other half. this way you can have a solid ground plane, but it acts like 2 ground planes (analog and digital) joined only under the chips that are both analog and digital. if you want to be extra sure,separate AVDD and DVDD on the ADS1219 (i.e. connect 3.3V to reset and DVDD lines rather than 5V to both).
Also you can see the "blocks". top right corner is the linear regulator section, to its left are the mixed signal chips (DAC and ADC), under those there is the reference voltage (layout copied from T.I datasheet with minimal routing changes), the two LDOs and their caps, and the digital stuff on the very left. I hope this helped you clean up your board a bit. I used too large of a package (1206) which makes things look less neat, but I think yours were 0603 so you should be fine in that regard. just keep the layout like the schematic (i.e. in blocks) and be careful of the mixed signal chips. that should be it. just make sure you have the switching regulator on the digital side, not the analog :-DD
nemail2:
Hi
Thanks for drawing that example. However I'm still not sure how I should do this with my design.
I mean, I have this already:
- digital and analog traces are separated, only the SPI and I2C lines necessary for the DAC and ADC go to the analog part of the board (lower part is digital, upper part is analog)
- current return paths should be reasonably short everywhere
- ground planes are split and star grounded, teensy 3.5 has a ferrite bead which connects the AGND pin (which is connected to the analog part of my board) to the GND pin (which is connected to the digital part of my board)
- all traces as short as possible or at least reasonably short, at least for the analog part
- all power supply traces are big ass
- separate LDOs and VREGs for digital and analog circuitry
- no switching regulators on the analog side
i admit, what's not ideal in my opinion or rather say what i really think to understand whats not ideal:
- I2C traces are quite long
- SPI are as well, as I need SPI for the DACs and for the Display as well, which is on the opposite side of the teensy board on the digital side and the DAC is obviously on the analog side
- power supply traces (27V and 15V) are quite long because i just need them in totally different sections of the board
- NTC trace (TH0) goes from the TIP3055 footprint all the way down to an analog input of the teensy 3.5 -> quite long trace as well
for none of these issues I have a solution. I have simply no idea on how to solve those issues - the board is quite large and a bit complex as well (at least for a beginner like me) and many things are already tightly packed and I simply do not know how to make the layout better.
even if I'd relayout everything, I'm pretty sure I'd end up in a similar layout (if not worse) like I have now.
Of course I don't expect you to do my project for me but I'd be really curious how you would layout this design. I just can't see how your clean but simple example layout could scale to a design like mine and still stay as clean as yours is. At least not if I'd do the layout.
I have done some more cleanup and a bit of relayouting to reduce the size of the board and make some traces shorter and I have updated the github repository with the lastest version:
https://github.com/mamama1/LabPSU_Darlington/raw/master/preview.PNG
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