Step-by-step Calculation of Feedback Resistors in Operational Amplifier Configurations

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Feedback resistors are essential components in operational amplifier (op-amp) circuits. They determine the gain and stability of the system. This article provides a clear, step-by-step guide to calculating feedback resistors in various op-amp configurations.

Understanding Op-Amp Feedback Configurations

Operational amplifiers can be configured in different ways, primarily as inverting, non-inverting, or differential amplifiers. Each configuration uses feedback resistors to set the desired gain and response characteristics.

Calculating Feedback Resistors in Inverting Amplifiers

In an inverting amplifier, the gain is determined by two resistors: the input resistor (Rin) and the feedback resistor (Rf). The formula for gain (Av) is:

Av = – Rf / Rin

To find Rf, rearrange the formula:

Rf = – Av × Rin

Choose Rin based on input impedance requirements, then calculate Rf accordingly.

Calculating Feedback Resistors in Non-Inverting Amplifiers

In a non-inverting amplifier, the gain is set by Rf and Rg (ground resistor). The formula is:

Av = 1 + Rf / Rg

To find Rf, rearrange:

Rf = (Av – 1) × Rg

Select Rg based on input impedance, then compute Rf for the desired gain.

Summary of Calculation Steps

  • Determine the desired gain (Av).
  • Select appropriate resistor values based on circuit requirements.
  • Use the relevant formula to calculate the feedback resistor.
  • Verify the resistor values are practical and within component limits.