# Reduce input voltage into a simple differential opamp circuit

Discussion in 'Analog & Mixed-Signal Design' started by Travm, Jul 5, 2017.

1. ### Travm Thread Starter Member

Aug 16, 2016
256
22
I completely disagree with your assessment of that. I have some new ideas on where to look for information, but i certainly haven't had a single question addressed.
I understand i'm not paying, and appreciate the fact you guys even read my words, but if you think i'm tone deaf... you haven't addressed post 1.

2. ### crutschow Expert

Mar 14, 2008
22,553
6,623
I said I was out but I'll leave one more comment, since it's hard to ignore such technical arrogance.
You keep insisting all you need is the mathematical analysis of your circuit that you say works.
But we are not interested in going to the significant effort of determining the math for an odd-ball circuit that we know will not work properly.
We tried to show you what will work and you keep insisting that a simpler circuit will work.
That's why you are tone deaf.
You are insisting that your square wheel will work, whereas it's apparent to everyone else you really need a round one.

3. ### Bordodynov Well-Known Member

May 20, 2015
2,291
704
I agree with the previous speaker. You have chosen a dead-end path. Carefully study my last drawing. There is no need to reduce voltages by voltage dividers. Take a suitable operational amplifier and build a classical differential amplifier. The operational amplifier is powered from 15 V. You just have to use a limiter to protect the ADC.

4. ### Travm Thread Starter Member

Aug 16, 2016
256
22

This appears to work pretty good to me?...
Just want to be able to figure in numbers what is happening to the gain when I add these two more resistors to the classical differential op amp circuit.

5. ### Bordodynov Well-Known Member

May 20, 2015
2,291
704
The world is not perfect. There is a scatter in the parameters of the resistors. See the post # 31. This fact makes your idea useless! Not even an accuracy of 0.1% is enough. Or will you do a precision (perhaps laser) fitting of the resistor values?!

Aug 1, 2013
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Post 25.
Post 39.

ak

7. ### Travm Thread Starter Member

Aug 16, 2016
256
22
Post 25 references post 23, which is not my circuit?
Thenevenin equivalents are a new concept for me, so it might take a while to get anywhere with that.

Aug 16, 2016
256
22