Q4Analog Circuits

Question

Explain the summing amplifier in detail.

Answer 1

A Summing Amplifier (or Adder) is an operational amplifier circuit that combines multiple input voltage signals into a single output voltage. It is typically configured as an inverting amplifier.

Multiple input voltages ( $V_{1}, V_{2}, V_{3}$ ) are connected through individual resistors ( $R_{1}, R_{2}, R_{3}$ ) to the inverting (-) terminal of the op-amp. The non-inverting (+) terminal is grounded. Due to the 'Virtual Ground' concept, the inverting terminal is also essentially at zero volts.

By applying Kirchhoff's Current Law (KCL) at the inverting node, the sum of the input currents must equal the current flowing through the feedback resistor $R_{f}$ :

Solving for the output voltage:

If all resistors are equal ( $R_{1} = R_{2} = R_{3} = R_{f}$ ), it acts as a direct summer: $V_{o u t} = - (V_{1} + V_{2} + V_{3})$ . If the resistors differ, it acts as a scaling/weighted summer, which is the foundational concept behind Digital-to-Analog Converters (DACs).

Q4Analog Circuits

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