Understanding Op Amp Weighting Factors: Homework Question Explained

[Phyisab****]

Homework Statement

I have a question which asks for the weighting factors associated with several input voltages to an op amp. What is meant by this? This terminology isn't used anywhere in the text.

 

[Zryn]

If you could post the picture of the circuit the question is referring to, it would help significantly.

Could it be talking about a Summing Op-Amp with different resistance values on each input, which would give each input a different gain (or weighting)?

 

[Phyisab****]

Yes that's it. In that situation how would you define the weighting factor? The ratio of one input to the output, when all other inputs are zero?

 

[Zryn]

That sounds right.

Mathematically, do you know how to analyze an Op-Amps? If you are able, you will get a transfer function that resembles:

$$V_{out}$$ = - $$R_{f}$$ * ( $$\frac{V1}{R1}$$ + $$\frac{V2}{R2}$$ + ... + $$\frac{Vn}{Rn}$$ )

When R1 = R2 = ... = Rn = R, you can merely add the voltages as they will all have the same Gain ( $$\frac{R_{f}}{R}$$ ), however if each resistance is not equal then the Gain will give each voltage a different weight.