And examples can be even more strange: we had DC-DC converter modules failing to work properly because one of the converter's power pins feeding an internal linear regulator picked up noise from the same converter.

Regards,
Istvan Novak



John Woodgate wrote:
I agree. One particular point is keeping a trace connected to an inverting input very short, even if that means including a low-value  'stopper' resistor close to the chip. That point has quasi-infinite sensitivity but infinitesimal impedance only within the op-amp pass band. Above the pass-band, it is an antenna connected to a diode. And yes, it can pick up power rail noise.

John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK

On 2018-04-09 04:27, Doug Smith wrote:
Hi Ken and the group,

Many analog circuits, as well as the analog parts of large ICs that you mention, do have response to GHz noise even 1 MHz unity gain opamps! Low frequency op amps can  generate a DC offset on their inputs from GHz digital noise or radio signals, a common problem for the last  45 years since I first observed it. Power supply rejection of op amps goes to pot pretty quickly with frequency as well. High frequency effects therefore are important even to low speed analog circuits. In some ways, one must lay out the low frequency analog circuit using microwave techniques to keep RF noise at bay. The circuit features must be keep really small,, including the bypass capacitors being kept extremely close (< 100 mils) to the op amp.

45 years ago, faced with opamp problems from RF noise I developed some techniques for keeping the op amps happy. I discuss these in my upcoming course.

Doug

University of Oxford, Course Tutor
Department for Continuing Education
Oxford, Oxfordshire, United Kingdom
--------------------------------------------------
Doug Smith
P.O. Box 60941
Boulder City, NV 89006-0941
TEL/FAX: 702-570-6108/570-6013
Mobile: 408-858-4528
Email: d...@dsmith.org
Web: http://www.dsmith.org
--------------------------------------------------




-
----------------------------------------------------------------
This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org>

All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html

Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc.

Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Scott Douglas <sdoug...@ieee.org>
Mike Cantwell <mcantw...@ieee.org>

For policy questions, send mail to:
Jim Bacher:  <j.bac...@ieee.org>
David Heald: <dhe...@gmail.com>

-
----------------------------------------------------------------
This message is from the IEEE Product Safety Engineering Society emc-pstc discussion 
list. To post a message to the list, send your e-mail to <emc-p...@ieee.org>

All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html

Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used 
formats), large files, etc.

Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Scott Douglas <sdoug...@ieee.org>
Mike Cantwell <mcantw...@ieee.org>

For policy questions, send mail to:
Jim Bacher:  <j.bac...@ieee.org>
David Heald: <dhe...@gmail.com>

Reply via email to