Hello, my tutor has asked me to sketch a non-inverting summing amp with three inputs.
I understand all the other common amp configurations, but I am unsure how to sketch this one.
Can someone please show me a basic example with some figures so I can clearly see how the individual gains are calculated with three inputs ?

Thanks kindly for any help.
(I have searched the web, but most examples just have formulas rather than actual figures)

 

Are you allowed to use two opamps? If so, then add an inverting unity gain opamp to the output of your inverting summing amplifier.

hgmjr

 

The 'net is a good source for such a circuit. Any search engine will find examples.

You might be interested in a thread we had on the subject - http://forum.allaboutcircuits.com/showthread.php?p=170314

 

thanks, great advice,
Would this attached sketch work.
I need gains of 4, 10 and 15.

Thanks kindly

 

thanks, great advice,
Would this attached sketch work.
I need gains of 4, 10 and 15.

Thanks kindly

Sorry that will not do the trick. You have used a non-inverting unity gain buffer. What you need is an inverting unity gain amplifier.

hgmjr

 

I didn't bother checking gains, you should be able to do that.

.

 

Thanks Bill. That is what I was suggesting.

hgmjr

 

thanks guys, I really appreciate your help.

 

excuse my ignorance, but can I just ask why the two 2x 1K ohm resistors are in place ?

Thanks kindly.

 

It is a unity gain inverter circuit. Which is why converts the first inverting circuit into a non inverting circuit per your requirements.

The exact resistors values aren't important, they need to be the same values for unity gain.

 

A few minutes in our Ebook will explain - http://www.allaboutcircuits.com/vol_3/chpt_8/5.html