Routing signals under crystals

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- Mark Borgerson
  
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posted
10 years ago

Sat, Aug 24, 2013 4:59 PM

I think you're correct in that the EMI occurs on the power supply lines, rather than in the chip itself. I've taken the usual steps---decoupling to the ground plane etc. I've also used a separate linear regulator for the SD card power.

When writing, the SD card seems to draw >50mA for microseconds at a time---it's difficult to tell exactly as the bandwidth of my current sensor isn't that high and the current pulses are (I hope) modified by the regulator and bypass capacitors.

I wonder if the noise relates directly to the current demands of the flash memory's charge pump that generates the programming voltage. When I get time, I'll take my RF sniffer (an old portable radio) and see if there's a significant difference in EMI between reads and writes.

Mark Borgerson

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- Randy Yates
  
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posted
10 years ago

Sun, Aug 25, 2013 2:27 AM

How do you know where it's coming from? Do you have screen rooms, antennae, spectrum analyzers, etc., like FCC testing centers do?

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Randy Yates 
Digital Signal Labs 
http://www.digitalsignallabs.com

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- rickman
  
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posted
10 years ago

Sun, Aug 25, 2013 8:20 PM

Lol, if you have EMI, you fix the board and it goes away, that shows it wasn't the chip... Same with the SD card. Replace the SD card with a different brand and the EMI should change or go away.

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Rick

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- Randy Yates
  
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posted
10 years ago

Mon, Aug 26, 2013 1:04 AM

Sure. But remember all those funny interactions you were talking about?

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Randy Yates 
Digital Signal Labs 
http://www.digitalsignallabs.com

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- rickman
  
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posted
10 years ago

Tue, Aug 27, 2013 4:49 PM

No, I don't. The point is that if the chip were faulty you would not be able to fix it in the board. If you can design a board that limits the EMI of the design, then by definition the problem is not the chip.

Are you suggesting that the board could be designed in a way that it creates EMI that emanates from the chip? My point is that the chip or SD card can be used in a design so that doesn't generate EMI or the chip generates EMI no matter what you do. I don't really care what ends up being the antenna because that is a pointless distinction.

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Rick