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Keeping specs of 18-bit DAC
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ezalys:
Hey all,
I'm interested in laying out a board with an 18-bit DAC on it. Besides careful power distribution, layout, grounding, and thermals, what other considerations should I make for preventing switching noise or other things from ruining the performance of the output? This thing will be in the same chassis (eurorack) as a raspberry pi-- so I'm very concerned about radiated EMI making its way into the output signal. I was thinking of using a board-level shield over the converter, and then running the output signal through the inside of the board up to the SMA connector. Is this a winning strategy?
Best wishes,
E
mawyatt:
We used the TI ISO1541 to isolate the data lines for a 16 bit ADC and DAC operating with the RPi. This allows a separate power supply with separate grounds for the ADC and DAC.
Best,
Micke:
I did some quite similar recently, built an accurate ACV/DCV voltage source...
D/A was 20-bit AD5791, controlled via SPI @15MHz by a dsPIC33 @128MHz
Might be some inspiration! https://www.eevblog.com/forum/metrology/diy-acvdcv-calibrator-with-ad5791/
I used a 4-layer board, stackup:
Top: Signals and available space Ground planes (Digital and Analog)
Inner1: +15V
Inner2: -15V
Bottom: Ground planes (Digital and Analog)
The only connection between Digital and Analog ground is made on Bottom side of PCB, under the D/A converter. I opened up a rectangular area in the solder mask to be able to solder a wire between the two ground planes.
Used lots of filtering with ferrites and decoupling on the supples, isolated SPI interface and dedicated ground planes.
Important is to not place components or traces in "wrong" place, digital and analog traces and components must not be placed in same zone (on any layer). Good luck with your project! :)
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