PCM2902 analog--digital grounds

jmar · 10th August 2005, 02:42 PM

I see in many schematics for this part that the analog and digital grounds are seperated by a 10 ohm resistor.

I thought instead on my board that I would try to create (if possible) isolated traces on all analog and digital connections with every trace grounded at the filter cap ground.

Wouldn't that be a superior method....and could I eliminate the 10 ohm resistor?

THANKS.

--Mike

kevinkr · 10th August 2005, 06:02 PM

I wouldn't recommend this due to the inductance of the individual traces. I would read the application notes and see if they provide any general guidelines.

Conventional practice with DACs has been to have a digital ground plane and an analog ground plane that meet at just one point under the dac, and this seems like pretty good practice for a 2902 as well.

In some cases one very solid ground plane has been used with good results as well.

Kevin

Guido Tent · 10th August 2005, 07:46 PM

Quote:

Originally posted by kevinkr
I I would read the application notes and see if they provide any general guidelines.

Kevin

I wouldn't trust them "by default".....

jmar · 11th August 2005, 02:25 PM

So the resistor isn't needed?

I thought the star system of dedicated traces and a SINGLE grounding point was ideal in any system?

I need to learn more about this......a large (low inductance) ground plane vs the star system.

Perhaps I should do the analog grounds in a star and use a single ground plane for the digital with everything going to the chip ground?

Guido Tent · 11th August 2005, 02:43 PM

Quote:

Originally posted by jmar
So the resistor isn't needed?

I need to learn more about this......a large (low inductance) ground plane vs the star system.

the resistor is a potential danger

I put my thoughts on paper, long ago

http://www.tentlabs.com/Info/Article...decoupling.pdf

It may help you in learning about the subject

Again, don't trust semiconductors manufacturers app notes, I once improved a demo board using my philiosophy: The jitter decreased by a fair amount and noise went down 30 dB........

cheers

Jocko Homo · 11th August 2005, 04:15 PM

He is right..........I found out the hard way not to listen to semi manufacturers. Anyone who closely examines some of my old stuff may find that out.

Jocko

jmar · 11th August 2005, 04:36 PM

wow.

nice bit of reading for me.....thanks very much.

--Mike

jmar · 12th August 2005, 12:49 PM

Is there an advantage at all to having (completely) seperate power supplys?

One for the analog DC....the other for the digital?

With completely isolated ground planes for each?

Guido Tent · 12th August 2005, 08:19 PM

Quote:

Originally posted by jmar
Is there an advantage at all to having (completely) seperate power supplys?

One for the analog DC....the other for the digital?

With completely isolated ground planes for each?

Hi

Yes, crosstalk should be avoided, so seperating power supply circuits and decoupling helps

On the groundplanes: Did you finish my article yet ?

best regards

kevinkr · 12th August 2005, 08:43 PM

Hi Guido,
Good article, I do many of the things you mention when I design a board. Perhaps I read your article long ago.. LOL

Kevin

10th August 2005, 02:42 PM	#1
jmar diyAudio Member Join Date: Jan 2004 Location: Indiana	PCM2902 analog--digital grounds I see in many schematics for this part that the analog and digital grounds are seperated by a 10 ohm resistor. I thought instead on my board that I would try to create (if possible) isolated traces on all analog and digital connections with every trace grounded at the filter cap ground. Wouldn't that be a superior method....and could I eliminate the 10 ohm resistor? THANKS. --Mike

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Digital or analog?	xplod1236	Digital Source	1	19th May 2005 02:15 AM
Analog vs. Digital XO	Seth Smith	Multi-Way	11	1st June 2004 09:33 PM
digital or analog	electro samurai	Analogue Source	7	29th February 2004 05:23 PM
Confused about Analog / Digital Grounds - TDA1541A	HeadSh0T	Digital Source	2	17th April 2003 04:27 PM
Analog to Digital?	Ioannis	Digital Source	5	11th December 2001 06:52 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

10th August 2005, 06:02 PM	#2
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	I wouldn't recommend this due to the inductance of the individual traces. I would read the application notes and see if they provide any general guidelines. Conventional practice with DACs has been to have a digital ground plane and an analog ground plane that meet at just one point under the dac, and this seems like pretty good practice for a 2902 as well. In some cases one very solid ground plane has been used with good results as well. Kevin

11th August 2005, 02:25 PM	#4
jmar diyAudio Member Join Date: Jan 2004 Location: Indiana	So the resistor isn't needed? I thought the star system of dedicated traces and a SINGLE grounding point was ideal in any system? I need to learn more about this......a large (low inductance) ground plane vs the star system. Perhaps I should do the analog grounds in a star and use a single ground plane for the digital with everything going to the chip ground?

11th August 2005, 04:15 PM	#6
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	He is right..........I found out the hard way not to listen to semi manufacturers. Anyone who closely examines some of my old stuff may find that out. Jocko

11th August 2005, 04:36 PM	#7
jmar diyAudio Member Join Date: Jan 2004 Location: Indiana	wow. nice bit of reading for me.....thanks very much. --Mike

12th August 2005, 12:49 PM	#8
jmar diyAudio Member Join Date: Jan 2004 Location: Indiana	Is there an advantage at all to having (completely) seperate power supplys? One for the analog DC....the other for the digital? With completely isolated ground planes for each?

12th August 2005, 08:43 PM	#10
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Hi Guido, Good article, I do many of the things you mention when I design a board. Perhaps I read your article long ago.. LOL Kevin

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)