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Operational amplifier basics

In this article, we'll cover the basics of the operational amplifier. It explains what an operational amplifier is, what it is used for, which circuit symbols are used and how it basically works. This article belongs to our electrical engineering division.

An operational amplifier is an electronic amplifier. It is used as a component in circuits, for example to amplify a weak signal. Before we take a closer look at the operational amplifier, you should take a quick look at the following list. If you are not yet familiar with the relevant topics, please take a look at them first. Because the knowledge in it is a prerequisite in order to be able to understand the following contents about the operational amplifier. Useful prior knowledge:


What do you need an operational amplifier for?

So I am now buying an operational amplifier to use in my electronic circuit. But what's that supposed to mean? What do you need it for anyway? Well, OPs - that's the short form - can be used, for example, in the following cases:

  • Amplify a signal, for example turn 1 volt into 2 volts.
  • Add two voltages, for example 2 V + 3 V = 5 V.
  • Subtract two voltages, for example 3 V - 1 V = 2 V.
  • Create a vibration.
  • Integrate a signal.
  • Switch a signal.
  • And much more.

In order to be able to fulfill the respective tasks, the operational amplifier must be wired with additional components (resistors, capacitors, etc.). We'll look at how to do this in later chapters. First of all, it is important to know that operating theaters can perform various tasks.


Circuit symbols old and new

We now know what an operational amplifier is and what it can be used for. Now, of course, when you draw a circuit, you also need a corresponding circuit symbol. Two symbols are usually used in electrical engineering and electronics. One that is now out of date and one that is current. The following picture shows you this:

In order for an operational amplifier to work, it needs a supply voltage. Depending on the request of the creator of the circuit, the supply voltages are drawn in or this is left unchanged. That depends on the overview or on the software. The supply voltage is of course necessary for it to function in practice.

Inputs and outputs

Now let's look at the various inputs and outputs of an operational amplifier. Basically, an OP first requires a supply voltage. This is usually symmetrical, for example +15 V and -15V or +12 V and -12 V). Then an operational amplifier has two inputs. The input with the "+" is called the non-inverting input, the input with the "-" is called the inverting input. And of course an operating room also has an exit. The following graphic shows this:

Operational amplifier functionality

There are entire books that deal with the operational amplifier and its wiring. A multitude of properties are also dealt with in such books. However, we will first take a look at the basic operation of an operating room. And then we very quickly end up with the terms differential voltage and differential gain.

Differential voltage:

We have a positive input (+) and a negative input (-). The differential voltage U lies between these two inputsD.. The following applies:

Example: We have a voltage of 3 mV at the positive input (+) and a voltage of 2 mV at the negative input (-). What is the differential voltage? Solution: UP. = 3 mV and UN = 2 mV. Then the differential voltage is UD. = 3 mV - 2 mV = 1 mV.

Differential gain:

The term "operational amplifier" already includes the word "amplifier". The operational amplifier amplifies the differential voltage just discussed (UD.). How high this differential gain (VD.) depends on the type of OP used. A gain of 100,000 or more is possible with a very large number of OPs. The following equation can be used to calculate the output voltage (UA.) of the operational amplifier.

Example 1: We have a differential voltage between the two inputs of -1 mV. The differential gain of the operational amplifier is 1000. How high is the output voltage? Solution: UA. = VD. · UD. = -1 mV 1000 = -1 V.

Example 2: We have a differential voltage of 0.6 mV. The gain is 106. The OP is supplied with +15 V and - 15 V voltage. What is the output voltage? Solution: UA. = VD. · UD. = 0.6 mV 106 = 600 V. In mathematical terms, 600 V should be present at the output. This is of course not possible because the OP is only supplied with +15 V and -15 V. And the output does not quite manage even this supply voltage. Therefore the output of the OP will not be at the calculated 600 V, but will be slightly below the +15 V supply voltage, i.e. about +14 V.


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