An ideal summing amplifier has Rf = 20 kOhm and two input resistors of 10 kOhm. If both input voltages are +1 V, the output is?

  • A-1 V
  • B-2 V
  • C-4 V
  • D+4 V
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Correct Answer: C. -4 V
Explanation: Vo = -Rf(V1/R1 + V2/R2) = -20k(1/10k + 1/10k) = -4 V.
Reference: Standard analog electronics: operational amplifiers
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