Grounding Idea for single opamps - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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
Reply
 
Thread Tools Search this Thread
Old 24th December 2005, 10:26 PM   #1
Franz G is offline Franz G  Switzerland
diyAudio Member
 
Franz G's Avatar
 
Join Date: Jun 2004
Location: Bern / Switzerland
Default Grounding Idea for single opamps

Everyone of you designing pcb's for opamps knows, how bad the layout of the single opamp is, concerning ground tracing between the bypass caps.

It's always a dilemma to create short and large traces between the bypass caps. Double sided is not a perfect solution, still some limitations for this current path.

So, tonight I had the idea to attach some kind of cupper cap on top of the chip, offering a good ground trace.

What do you think, would this have the disadvantage to add some parasitic capacitance to the other pins?

Here the first try, to illustrate the idea. It would have the advantage to act as little heathsink and therefore stabilizing the amp.

Franz
Attached Images
File Type: jpg grounding_idea.jpg (80.4 KB, 595 views)
  Reply With Quote
Old 24th December 2005, 10:42 PM   #2
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
No bearing on your concept other than finetuneing, I have seen pictures of the charge buildup on the plates in those glass lab capacitors (lyden jar?) anyway, what stuck with me is that the patern seemed to radiate more from sharp edges, and basicaly only radiates on edges overall, so maybe you want to sand the edges down some... come on, I know you like playing with your metal tools, i just discovered my grandads metal working tools this weekend, he had 3 lathes at home when I was little.
  Reply With Quote
Old 24th December 2005, 10:46 PM   #3
joensd is offline joensd  Germany
diyAudio Member
 
Join Date: Dec 2001
Location: Germany
Only advantage I see is the "cage" you create with your grounded cap.
Good against HF radiation.
And of course the extra cooling.

As to grounding I´d think that a "short as possible" lead below the IC (or ground layer) would have less inductance.
(especially with the bents in the copper sheet).
Then again we´re talking audio so that doesn´t matter as much as in digital circuitry for example.

Of course you´d still have to sort out grounding anyway as the opamp wouldn´t be your only element in the circuit?

greets & happy christmas days
Jens
__________________
jens
  Reply With Quote
Old 25th December 2005, 07:45 AM   #4
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Franz, I think you should analyze your situation a bit more. What was the problem? I think you enviromnent is pretty good if you have a groundplane and a normal doublesided board. One way to make things better is to use SMD parts with will be tighter to the board and are also smaller with means better chance of good decoupling.

1 sqcm on a pcb => 3 pF
__________________
/Per-Anders (my first name) or P-A as my friends call me
  Reply With Quote
Old 27th December 2005, 09:14 AM   #5
diyAudio Member
 
Mr. Triatic's Avatar
 
Join Date: Feb 2002
Location: SWE EU
i just say thin PTFE double sided PCB-material, its good enough for microwaves so i guess it will be ok for audio as well 8-)

Seriously speaking, shielding is good so there is nothing wrong with an "IC-cap" made of copper but i dont think it is necessary, not even with highspeed opamps..

If you want a short path to ground, use SMD capacitors and place them underneath a DIP opamp and plate through to the groundplane side of the PCB.
__________________
www.joddla.net/audio/
  Reply With Quote
Old 27th December 2005, 10:18 AM   #6
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Teflon is OK but it is very soft => not so good.
__________________
/Per-Anders (my first name) or P-A as my friends call me
  Reply With Quote
Old 28th December 2005, 07:28 AM   #7
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Default Re: Grounding Idea for single opamps

Quote:
Originally posted by Franz G
Double sided is not a perfect solution,
Yes it is compared to a singlesided board.
__________________
/Per-Anders (my first name) or P-A as my friends call me
  Reply With Quote
Old 28th December 2005, 03:00 PM   #8
Banned
 
Join Date: Mar 2003
Location: Lisbon, Portugal
Quote:
Originally posted by Franz G
It's always a dilemma to create short and large traces between the bypass caps. Double sided is not a perfect solution, still some limitations for this current path.

So, tonight I had the idea to attach some kind of cupper cap on top of the chip, offering a good ground trace.

What do you think, would this have the disadvantage to add some parasitic capacitance to the other pins?
Yes, you are capacitive coupling the signal pins.

Franz, how hard can it be?
Simple.
Single layer, of course.
Attached Images
File Type: png op-amp bypass.png (3.7 KB, 256 views)
  Reply With Quote
Old 28th December 2005, 03:04 PM   #9
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Easy if it won't draw any traces under the opamp....
__________________
/Per-Anders (my first name) or P-A as my friends call me
  Reply With Quote
Old 28th December 2005, 03:19 PM   #10
Banned
 
Join Date: Mar 2003
Location: Lisbon, Portugal
Quote:
Originally posted by peranders
Easy if it won't draw any traces under the opamp....
Do you find it hard to put a feedback resistor there?
An SMD resistor can be put there easily, and the ground trace can be a little thinner.
Also, smaller bypass caps (SMD if you want) can easily be placed right after the electrolythics.
This layout is very good for modern, fast, wide bandwidth op-amps.
I don't understand the need for double layer, when there is no need. It may be good only as a show-off.

Also, return the currents to a central point (a star ground) instead of undeliberately using a ground plane for that, which should only serve for shielding, connected to one ground point on the circuit.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Grounding with single tap secondary... Nordic Tubes / Valves 1 13th May 2008 03:42 PM
Grounding of opamps. Signal or Power? Arx Chip Amps 1 23rd July 2007 09:47 AM
Stacking single opamps Swifty Digital Source 2 25th April 2006 03:03 PM
Single Opamps keyne Solid State 1 15th April 2004 02:27 PM
Good single rail opamps Bricolo Solid State 27 24th January 2003 05:05 PM


New To Site? Need Help?

All times are GMT. The time now is 02:15 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2