« Driveway Lightning - John Dunn, Consultant, Ambertec, P.E., P.C. | Main | PWM Chip Slow CLK Fall Time - John Dunn, Consultant, Ambertec, P.E., P.C. »

September 22, 2011


Feed You can follow this conversation by subscribing to the comment feed for this post.

george storm

I agree that this is almost always a third-best way of dealing with interference - even though any ringing or instability can nearly always be corrected - either via a small capacitor in parallel with the feedback resistor or a small resistor in series with the filter capacitor (the value of either of which is easily calculated).

Apart from any other reasons, the method as proposed does nothing to reduce the common-mode component - and not many OPAMPs are designed to be tolerant to common mode signals that lie outside the operating frequency range.

Vladimir Doubovis

The capacitor C3 together with resistor R3 is working as the integrator that creates delay in feedback loop, so higher T=R3*C3 should create higher instability. It is matching to your pictures instability levels for 100K and 40k.
Ideally this capacitor should not be used, excluding a case when you need to boost gain at high frequencies.

Roy Laurnet

I use RC decoupling to the power pins and on the PCB, I keep the inputs as short as possible to help prevent EMI issues. When dealing with extremely sensitive circuitry, I use the "mecca grounding" technique for adjoining stages. Keeps thing mighty quiet and fairly free from EMI too.


a care full analysis helps on use of C3 cap. It causes effect on ac gain and reduced phase margin. So some one need to analyse the trade off between immunity needs vs output ringing and gain stability

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been saved. Comments are moderated and will not appear until approved by the author. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment

Comments are moderated, and will not appear until the author has approved them.

Your Information

(Name and email address are required. Email address will not be displayed with the comment.)


  Learn about our  

 free engineering 

consulting referral 

      service at:


  IEEE Consultant's 

      Network of 

     Long Island


We have over forty 

electrical, electronic, 

mechanical and 

software engineers 

with expertise in more 

than sixty-five categories 

of technology and business. 

All are members of the 

IEEE and adhere to the 

IEEE professional codes 

of ethics. 

No fee is charged for the

referral service. 

Each member is an 

independent consultant 

and negotiates his/her 

own consulting agreement.


Editor: Jerry Brown


John Dunn

Marty Kanner

Murray Kleiner

Dick LaRosa

David Pinkowitz

Carl Schwab

Gerry Bodner

Larry Rachman


Unless otherwise noted, 

reprinting or republication 

of anarticle on this blog is 

authorized by crediting the 

author and prominently 

displaying the following 

sentence at the beginning 

or end of the article,

including the hyperlink to

IEEE Consultant's Network 

of Long Island

"This report is republished 

with permission of IEEE 

Consultant's Network of 

Long Island"



Blog powered by Typepad

Enter your email address:

Delivered by FeedBurner