# How to offset output voltage without using DC offset

Discussion in 'Homework Help' started by justaspare, Apr 10, 2016.

1. ### justaspare Thread Starter New Member

Apr 9, 2016
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I'm supposed to be building a circuit that has an input from a function generator of 20v p-p, however the output measured on the oscilloscope needs to be 10vp-p with the positive side at 6v and the negative side at -4v. I have the voltage devider part covered, but I'm unsure how to go about offsetting the

I need to do this without using the DC offset in the function generator. Would this work with just a basic amplifier or attunator circuit? The cosest thing I have found involves op-amps, and my text doesnt have anything similar to this request in it, so I'm not sure where to go from here.

2. ### ErnieM AAC Fanatic!

Apr 24, 2011
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You can make 10vpp from 20vpp with a simple 2:1 voltage divider, which will be centered on zero.

If you now take that same divider and connect it to -8v instead of ground the net signal will be offset by the -4 v you want.

You can prove that by superposition, first look at the output with one than the other source shorted out, then add them together.

3. ### dannyf Well-Known Member

Sep 13, 2015
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a summing amplifier will do - which is essentially an offset adjustment here.

4. ### SLK001 Well-Known Member

Nov 29, 2011
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This is like asking "How do I hammer a nail without a hammer?"

5. ### WBahn Moderator

Mar 31, 2012
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That was my first thought based on the title, but the TS clarifies that he is talking about without using the DC offset capability of the function generator.

6. ### justaspare Thread Starter New Member

Apr 9, 2016
2
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That's what you get with the teacher I have. The first part of the assignment called for a voltage devider but ONLY gave input voltage and output voltage. He told me that we weren't supposed to make up the total resistance and then he made up the total resistance 45 minutes into the lab. We needed 3 different divisions, or it would have been a non-issue.

Last edited: Apr 10, 2016
7. ### dannyf Well-Known Member

Sep 13, 2015
2,196
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Vout = 0.5 * (Vin + 2)