# non-inverting summing amp

Discussion in 'Homework Help' started by fran1942, Sep 3, 2010.

1. ### fran1942 Thread Starter Member

Jul 26, 2010
58
0
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)

2. ### hgmjr Moderator

Jan 28, 2005
9,030
214
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

Apr 20, 2004
15,815
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4. ### fran1942 Thread Starter Member

Jul 26, 2010
58
0
Would this attached sketch work.
I need gains of 4, 10 and 15.

Thanks kindly

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5. ### hgmjr Moderator

Jan 28, 2005
9,030
214
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

6. ### Wendy Moderator

Mar 24, 2008
20,735
2,499

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

.

File size:
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7. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Thanks Bill. That is what I was suggesting.

hgmjr

8. ### fran1942 Thread Starter Member

Jul 26, 2010
58
0
thanks guys, I really appreciate your help.

9. ### fran1942 Thread Starter Member

Jul 26, 2010
58
0
excuse my ignorance, but can I just ask why the two 2x 1K ohm resistors are in place ?

Thanks kindly.

10. ### Wendy Moderator

Mar 24, 2008
20,735
2,499
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.

Apr 20, 2004
15,815
282