EEG board using ADS1299 chip. Help on PCB design

Thread Starter

Andrea Antonello

Joined Feb 15, 2018
9
Hello everyone!
I am a robotics engineer based in London and I have interest in sensing and electronics. As a part of a personal project, I want to design my own EEG setup (potentially to control a robot). I stumbled open work done by other people/companies, and the ADC of choice seems to be the ADS1299 from Texas Instrument.
I have a lot of experience with analog PCBs (I design PCBs for guitar amps), however I never had the chance to do SMD boards for sensing: I figured this would be a great learning experience :)
I have created my schematics and layouts in Eagle and the board is basically completed. I would love to have some expert opinion o the results, and any suggestions you might have that might increase the chances of success :)
A couple of things to note/doubts:
- I'm using a 2 layers PCB
- ground planes and fence vias on both sides
- I'm using an external oscillator for the clock: not sure the location of it on the board is best to avoid noise/interference
- I tried to separate the analog and digital signals, not sure if this is the best practice
- I'll be using SPI communication with a Raspberry PI (never used SPI before, so I hope the wiring is correct)
- I kept the supply and filtering components quite far from the chip and the digital signals as much as possible
Please let me know your thoughts, hope to learn more about circuit design and add some knowledge to my toolbox :)
Andrea
View attachment schematic_brain.pngall_brain.pngpads_brain.pngtop_brain.pngbottom_brain.png
 

seanstevens

Joined Sep 22, 2009
164
Hi @ Andrea,
Its very difficult to follow the circuit and the tracking like this. I have a massive interest in EEG monitors. I have also designed some in the past using opamps/instrumentation amps and AD and multiplexer etc when such a large all-scale integration wasnt available.

I presume you have read through the recommendation for the layout in the datasheet? A star configuration is recommended for the AVDD/AVDD1, as far as I can see, your supply track goes directly to those pins so it should be OK.
What I would suggest though is some more vias under the main chip, there are a couple of patches of ground that could do with vias to the bottom layer rather than very thin links via the chip's pins.
Also, the datasheet gives you recommendations on the placement of the power supply and keeping the digital ground away from the analogue ground, as well as the flow of the signal. Essentially keep your analogue components and tracks well away from your noisy digital tracks.
SPI is simple enough, you only need the 4 pins that you already have marked in your circuit.

Sounds like an interesting project, good luck. I also have a similar EEG monitor planned, just havent had the time yet.
 
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