« Your clock battery still matters - by Dave Rost | Main | High Voltage Corona Test - John Dunn, Consultant, Ambertec, P.E., P.C. »

January 11, 2011


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

George Storm

Agreed that there will in principle always be multiple resonances, but fortunately there are design techniques that can minimise the heights of the peaks - though a low-impedance response over a wide bandwidth does not in general come "for free".

Of course, in this case the simplest way to avoid the 100-MHz parallel resonance would be to omit the 50-pF capacitor, as it does not appear to provide any noticeable benefit when its series resonance is as low as 100-MHz.

chin wong

What are we getting at here? As design people know, RF design board is quite different from regular multi layers mixed signal board. In additions, the layout is quite difference. The fr is about 3GHz, which is much higher than normal digital design. It would not have concerned for lower frequence stuff. There is a trick to minimize this issue with good RF layout.

John D.

Hi, George.

The resonant peak issue came to my attention in a real-world case of having trouble with a Xilinx FPGA. In this example, the highest self-resonant frequency capacitor is in the artwork itself and would not be possible to avoid that.

Clearly it is possible to design systems that work, but keeping an eye out for rail voltage bypass imepdance across the frequency spectrum of interest, possibly with the inclusion of damping element(s), would be prudent.

Carl Schwab

John this discussion here brings to mind the "Foster reactance theorem" that I was taught in 1949. The theorem was attributed to the telephone laboratories in 1922 and a fellow named Zobel. It postulated when you parallel connected series resonate OR series connected parallel resonate circuits, the impedance (or the inverse) would be a succession of alternating poles and zeros. Now in 1922 they hadn’t developed the concept of poles and zeros but they understood the principal.

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