State the formula for the output voltage of a summing amplifier with multiple inputs.

Vₒᵤₜ = −R_f(V₁/R₁ + V₂/R₂ + V₃/R₃ + …)

In the summing amplifier output equation, what determines the weighting applied to each input voltage?

The ratio of the feedback resistance to that input's resistance (R_f/Rₙ).

What function does a summing amplifier perform on multiple input signals?

It combines multiple input signals into a single output that is the inverted weighted sum of the inputs.

What does the negative sign in the summing amplifier output equation indicate?

It indicates phase inversion of the output relative to the inputs.

If all input signals to a summing amplifier are positive, what is the polarity of the output voltage?

The output voltage is negative, due to phase inversion.

How can a summing amplifier be configured to give different weightings to multiple input signals?

By using different input resistances for each input; the weighting for each input is determined by the ratio R_f/Rₙ.

AQA A-Level Physics 7408

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Electronics

Summing amplifier configuration

3 things to know
Paper 3, section B

Overview

The weighted sum of several inputs, and the difference amplifier that rejects a common signal.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

What is the output of a summing amplifier, and what sets each input's contribution?

Numbers

What does the minus sign mean, what sign is the output for positive inputs, and how are the inputs given different weightings?

Numbers

What does a difference amplifier do with a signal common to both inputs?

Questions from this subtopic

Each one with the model answer underneath.

1
State the formula for the output voltage of a summing amplifier with multiple inputs.
Model answer
Vₒᵤₜ = −R_f(V₁/R₁ + V₂/R₂ + V₃/R₃ + …)
2
In the summing amplifier output equation, what determines the weighting applied to each input voltage?
Model answer
The ratio of the feedback resistance to that input's resistance (R_f/Rₙ).
3
What function does a summing amplifier perform on multiple input signals?
Model answer
It combines multiple input signals into a single output that is the inverted weighted sum of the inputs.
4
What does the negative sign in the summing amplifier output equation indicate?
Model answer
It indicates phase inversion of the output relative to the inputs.
5
If all input signals to a summing amplifier are positive, what is the polarity of the output voltage?
Model answer
The output voltage is negative, due to phase inversion.
6
How can a summing amplifier be configured to give different weightings to multiple input signals?
Model answer
By using different input resistances for each input; the weighting for each input is determined by the ratio R_f/Rₙ.

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