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# Need help with designing Op-Amp circuit!

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#### the_risk_master

summing amplifier circuit

Hi all,

Just want to ask if anyone knows how to design an Op-Amp Circuit
with voltage input/out relation:

Vo=5V1+3V2-6V3-4V4-10V5

Any help?

regards

summing opamp circuit

Use the summing amplifier.
A summing amplifier has one feedback resistor and multiple resistors (as many as the inputs) connected to the inverting input. The output voltage is the sum of the individual input voltages, each amplified by the ratio of the feedback resistor and the corresponding input resistor, all inverted. In your case, the first two terms are positive, so you need another summing amplifier, whose output will be added to the last three terms.

Look at the picture and note the resistors ratios. Their actual values can be different from the ones shown, but the ratios must stay the same.

### the_risk_master

Points: 2

Thanks VVV that circuit is right.

Ive formulated a new solution for it (a short cut)

I'll post my solution later for others to review my solution

op amp circuit

y=4x'+3x+x/3 can anyone setup the opamp circuit for me?

text_opamps2.htm

Am I forgetting algebra?
What does x' mean?

Re: OP-AMP Circuit?

x'=derivative of x.

OP-AMP Circuit?

My higher maths is getting rusty, I'v started reading some mathematics books and parts of it are coming back. I'd have written that as dx/dx rarther than x'

A derivative of a function is the rate of change of a function. When X is a voltage that means x' is the rate at which the voltage is going up or down.

If X is a DC voltage eg 3volts then the derivative is zero. If x is a square wave with a 1nS rise time then
x' is zero most of the time and has a large spike 1nS wide at the state changes of x, x' may be very large eg 0 to 5V in 1nS is a slew rate of 5000,000,000 volts per second.

There is going to be a pratical limit on the accuracy of the circuit due to the frequency response of the opamp.

You are going to need a two input summing amplifier circuit.

The 3x+x/3 part can be implemented as an input with a gain of three and a third.

The x' part is going to require a differentiator circuit as shown at the bottom of this page.

I'm not going to do the maths for you.
You can play with resistor values in spice or electronics workbench if necessary.

Re: OP-AMP Circuit?

we must use a Differentiator amplifier and two Summing Amplifier.thank you for helping.x'=differantion of x too.we use x' almost everytime .and it must be ac voltage if we use x'.

OP-AMP Circuit?

Re: OP-AMP Circuit?

ok.

Re: OP-AMP Circuit?