×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

OP AMP CMRR Measurement?

OP AMP CMRR Measurement?

OP AMP CMRR Measurement?

(OP)
Hello all,

I am on a quest to understand the specifications for op-amps more clearly.

On this quest I am trying to measure the common mode rejection ration for a 741 op amp.

But I am at a bit of a loss how to measure considering the measurement needs to be very precise.

I have tried one method where I shorted the inverting and non-inverting inputs and then inserted a signal but this lead me no where definate.

Any enlightenment would be appreciated

Michael

RE: OP AMP CMRR Measurement?

Michael,

You may not have gone down deep enough with your ACVM on the output.  When you feed a signal, say 1kHz at 1 volt RMS, into the shorted pos & neg inputs, the output will be very low, say around millivolts or less.  A finely tuned CMR could be tens microvolts.  At this point you'll be competing with noise, too.  

Make sure the opamp is properly configured and working correctly before the CMR test.  An oscillascope is very useful to confirm proper operation, too.  The 741 is an old workhorse and lots of fun to play with.  

Cliff Michael

RE: OP AMP CMRR Measurement?

Hi There,

CMRR = Differential Gain/Common Mode Gain(of course!).

You are on the rigth track.Just ensure proper grounding of teh supply,use by passes for blocking stray currents,and then apply a 10Vp-p 1Khz Signal in Common Mode and Differential Mode.Just measure the gains and find the ratio.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close