Exam-style question
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How does a summing amplifier combine multiple input signals?.
- A.By adding the voltages at the non-inverting input
- B.By adding the currents at the inverting input and converting to voltage
- C.By subtracting the signals at the inverting input
- D.By multiplying the signals together
Model answer
What a good answer should say
- By adding the currents at the inverting input and converting to voltage
Explanation
Why this works
Formula: I_total = I1 + I2 + ...; Vout = -Rf * I_total. Substitution: I1 = V1/R1, I2 = V2/R2.
Working: Currents from each input add at the inverting node, multiplied by the feedback resistor gives the output voltage with a negative sign. Answer: It adds currents at the inverting input and converts to voltage.
Units: volts. Conclusion: Currents add at the inverting node, output is the negative sum.
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