# How to offset output voltage without using DC offset

#### justaspare

Joined Apr 9, 2016
2
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.

#### ErnieM

Joined Apr 24, 2011
8,362
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.

#### dannyf

Joined Sep 13, 2015
2,197
a summing amplifier will do - which is essentially an offset adjustment here.

#### SLK001

Joined Nov 29, 2011
1,548
This is like asking "How do I hammer a nail without a hammer?"

#### WBahn

Joined Mar 31, 2012
29,153
This is like asking "How do I hammer a nail without a hammer?"
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.

#### justaspare

Joined Apr 9, 2016
2
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.
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.

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#### dannyf

Joined Sep 13, 2015
2,197
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.
Vout = 0.5 * (Vin + 2)