An ideal op-amp summing amplifier has three equal 10 kOhm input resistors carrying inputs 1 V, 2 V and -1 V, with Rf = 10 kOhm. The output is?

  • A-2 V
  • B+2 V
  • C-4 V
  • D+4 V
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Correct Answer: A. -2 V
Explanation: For equal input and feedback resistors, Vo = -(V1+V2+V3) = -(1+2-1) = -2 V.
Reference: Standard analog electronics: operational amplifiers
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