Exam-style question
Try this first
Which statement best describes the output of a summing amplifier?.
- A.It is the sum of the input voltages
- B.It is the sum of the input currents multiplied by the feedback resistor
- C.It is the product of the input voltages
- D.It is the difference between the input voltages
Model answer
What a good answer should say
- It is the sum of the input currents multiplied by the feedback resistor
Explanation
Why this works
Formula: Vout = -(Rf/R1)V1 -(Rf/R2)V2 ... Substitution: Rf, R1, R2, V1, V2.
Working: Each input voltage is weighted by the ratio Rf/Ri and summed with a negative sign. Answer: It is the sum of the input currents multiplied by the feedback resistor.
Units: volts. Conclusion: The output is the negative sum of the weighted input voltages.
Common mistake
No common mistake is linked to this question yet.