Op-amps

From DP

The Operational Amplifier

Introduction

The operational amplifier is one of the most useful analog IC available, and one of the most daunting for beginners and experienced engineers. This page is to introduce some of the uses, and how to calculate values for the various configurations.

Simple non inverting

Below is a diagram of an op-amp in a closed loop non inverting configuration. Probably the most used configuration. Lets assume this is an ideal amplifier. R₁ is the input and R₂ is the feedback. When R₁ = R₂ the circuit is in unity(meaning input = output).

To calculate output use the following formula.

<math>\frac{r_2}{r_1}*V_in = V_out</math>

R₃ can be calculated by the following.

Example 1

In order to bring a 1V peak input to a 5v range we would need to R₂=5k and R₁=1k and R₃=833

and for R₃

lets graph it.

Example 2

Lets say that you want to measure a 12 volt max signal with a 3.3v a/d converter. Using the same formulas as before and standard resistor values.

and for R₃

lets graph it.

• While for these examples it is fine to assume an ideal amplifier. Many op-amps do not go rail to rail and have varying amounts of linearity. In the next section we will address these issues, and look at some other properties of common op-amps.