« Bidirectional Logarithmic Compression - John Dunn, Consultant, Ambertec, P.E., P.C. | Main | HYDRAULIC HYBRIDS---Carl Schwab »

October 13, 2011

Comments

george storm

Regarding bootstrapping the input resistance: when do such corcuits have a known and non-removable input resistance? Otherwise we do better either to buy a large-value resistor or to bootstrap using a follower with a potential divider at the output.

BTW, the AC-mode time constant of most 'scopes is set not by technology, but so that the user does not perceive an excessive delay before the signal settles. (Sorry to be a spoil-sport here)

John Dunn

That R1 was an RN55 or RN60 style (I forget which) and that style of film resistor didn't come in values of high enough ohms for the purpose at hand. Bootstrapping was the answer to that.

Fred Floru

Below is a link to an IC that uses a similar technique to boost just the common impedance of a differential amplifier.

http://thatcorp.com/datashts/THAT_1200-Series_Datasheet.pdf

Sergio Franco

Rewriting as Rin = R2/(R2/R1-R3/R4) better evidences that Rin depends on the difference between two resistance ratios. In applications where these ratios are designed to be very close to each other, a slight mismatch may alter Rin significantly, making it even infinite or negative, depending on the direction of the mismatch. So, even though the circuit is elegant in theory, one has to be aware of this feature when applying it in practice. Regards,

Sergio Franco

http://online.sfsu.edu/~sfranco/BookAnalog/AnalogJacket.pdf


Verify your Comment

Previewing your Comment

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

Working...
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.

Working...

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.)

Editor

  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

Contributors:

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"

 

Pages

Blog powered by Typepad

Enter your email address:

Delivered by FeedBurner