Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Input Noise Guarding of OPAmps
Input Noise Guarding of OPAmps
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 14th July 2007, 10:49 AM   #1
Jan Dupont is offline Jan Dupont  Denmark
diyAudio Member
 
Jan Dupont's Avatar
 
Join Date: Apr 2003
Location: Copenhagen, Denmark
Send a message via MSN to Jan Dupont
Default Input Noise Guarding of OPAmps

What's the best way to make Input Noise Guarding of OPAmp input circuits ??
Many uses Ground Plane, but BURR-BROWN recomends this:
Attached Images
File Type: jpg bb input guarding.jpg (57.2 KB, 274 views)
__________________
Free Schematic and Service Manual downloads www.audio-circuit.dk, Spare time company (just for fun): www.dupont-audio.com
  Reply With Quote
Old 14th July 2007, 01:10 PM   #2
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
That kind of guarding is usually for those that use cheap boards and want high impedance inputs (Teflon boards cost about $1 a square inch last time I checked).

I had to use a guard ring on a low frequency spectrum analyzer integrator cap, otherwise the charge would bleed off too fast.
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote
Old 14th July 2007, 01:15 PM   #3
Bonsai is offline Bonsai  Europe
Account disabled at member's request
 
Join Date: Jul 2003
Location: Europe
Jan, this technique usually has nothing to do with noise reduction as applied to audio. Basically, the idea of the guard is to prevent leakage currents on the PCB from upsetting the DC performance of the op-amp. The guard ring is tied to a low source impedance which is at the same potential as the inputs. This can be accomplished by buffering the feedback voltage divider with a second opamp. The guard ring intercepts any leakage currents arising from delta voltages elswhere on the pcb .

Note that or this echnique to work, a double ided PCB is required (if using more than 2 layers, GR is required on every layer).

Might reduce very low frequency leagage noice in an mc amp, but I only have (good) experience using this technique on thermocouple amps.
  Reply With Quote
Old 14th July 2007, 01:16 PM   #4
Bonsai is offline Bonsai  Europe
Account disabled at member's request
 
Join Date: Jul 2003
Location: Europe
good point from djk - giard ring is absolute must for integrator applications - usually in dual slope A-D applications
  Reply With Quote
Old 14th July 2007, 03:08 PM   #5
Jan Dupont is offline Jan Dupont  Denmark
diyAudio Member
 
Jan Dupont's Avatar
 
Join Date: Apr 2003
Location: Copenhagen, Denmark
Send a message via MSN to Jan Dupont
Thanks all

I was just wondering....
__________________
Free Schematic and Service Manual downloads www.audio-circuit.dk, Spare time company (just for fun): www.dupont-audio.com
  Reply With Quote
Old 14th July 2007, 04:09 PM   #6
Juergen Knoop is offline Juergen Knoop  Germany
diyAudio Member
 
Juergen Knoop's Avatar
 
Join Date: Jan 2007
to prevent leakage currents I bend the input-pins and wire them free air.
But thats not audio
regards
  Reply With Quote
Old 14th July 2007, 11:02 PM   #7
jackinnj is offline jackinnj  United States
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Input Noise Guarding of OPAmps
Quote:
Originally posted by juergenk
to prevent leakage currents I bend the input-pins and wire them free air.
But thats not audio
regards
called "dead bug" -- popular in low power ham radio applications as well.
  Reply With Quote
Old 15th July 2007, 03:58 AM   #8
Juergen Knoop is offline Juergen Knoop  Germany
diyAudio Member
 
Juergen Knoop's Avatar
 
Join Date: Jan 2007
I try to make use of sockets as much as possible
Attached Images
File Type: jpg s6300143.jpg (23.9 KB, 136 views)
  Reply With Quote
Old 15th July 2007, 04:37 AM   #9
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Input Noise Guarding of OPAmps
Hi ACD,
If you need to go to that extent, air currents can generate much more noise also. One of those things. Thermal drift is also noise, and once again air currents can really mess things up.

-Chris

Edit: Hi juergenk,
Sockets tend to make everything much worse. From capacitance to thermocouple effects. Many more paths for leakage too!
__________________
"Just because you can, doesn't mean you should" my Wife
  Reply With Quote
Old 15th July 2007, 05:02 AM   #10
Juergen Knoop is offline Juergen Knoop  Germany
diyAudio Member
 
Juergen Knoop's Avatar
 
Join Date: Jan 2007
Hi Chris,
thats not an audio circuit, the (+)input-pin is bend up to preserve the GOhm input impedance and avoid leakage currents.
The socket doesn't hurt in this special application.
Guess the hints in the BB datasheet weren't meant for audio circuits too.
Regards
  Reply With Quote

Reply


Input Noise Guarding of OPAmpsHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
FS: Capacitors/ Opamps/ Power Transistors/Noise Filters & Other Interesting Stuff dtm1962 Swap Meet 1 8th February 2006 04:21 PM
Reduce input noise YUTK Solid State 18 27th December 2005 12:04 PM
Low noise input? MikeW Pass Labs 11 21st September 2005 11:57 PM
T Amp input noise pixpop Class D 9 27th May 2005 04:54 PM
Input selector using PS gating of opamps? tcpip Solid State 11 24th February 2004 01:06 PM


New To Site? Need Help?

All times are GMT. The time now is 12:51 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki