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understanding operational amplifier

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PG1995

Active Member
Hi

Please note that I'm a beginner so please keep your replies simple and straightforward so that you could be understood and your effort fully appreciated. Thank you.

1: Why is operational amplifier or op-amp so called? Is there also something like non-operational amplifier?

2: As I see it operational amplifier could be modified to do different things with the input signal. For instance, it could be designed into an inverting amplifier, non-inverting amplifier, etc.

3: Is a simple oscillator also made from an op-amp?

4: Can you please provide me some link which shows me in images that how different type of amplifier, such as inverting amplifier or differential amplifier, affects the input signal? The Wikipedia page only gives math formulas.

Thank you very much for your help and time.

Best wishes
PG
 

crutschow

Well-Known Member
Most Helpful Member
1: Not sure where the word operational came from but it normally means a high-gain amplifier block with differential inputs. They have a bandwidth from DC to some upper limit which can vary from 1HMz to several hundred MHz.

There is no amplifier defined as a non-operational amplifier.

2: True. I call it the swiss army knife of amplifiers.

3: It can be made into various types of oscillators as your reference shows.

4: Look at https://en.wikipedia.org/wiki/Operational_amplifier_applications or this.
 

Reloadron

Well-Known Member
Most Helpful Member
If you want to understand operational amplifiers I suggest you start at the beginning. To understand the op-amp you need to understand what goes into it, the building blocks and how they are configured. People sometimes tend to place the cart before the horse if you get the idea.

Ron
 

Brevor

Member
Operational amplifiers were devoloped back in the days of analog computers. Back then they were built with vacuum tubes. They were called operational amplifiers because they could be configured to perform different arithmetic operations on analog voltages. Such as addition (summing amplifier), subtraction (differential amplifier), Multiplication (gain amplifier). Thats where the name comes from.
 

PG1995

Active Member
Thank you, everyone.

@crutschow: Your reply was helpful. Thanks for the help.

@Brevor: Thanks. Your explanation for why is op-amp called so is good one.


Best wishes
PG
 

PG1995

Active Member
1: A op-amp can be modified to do different things. For instance, it could be modified into a summing amplifier who does addition. But, is there anything in itself such as op-amp? What does it do? Or, is it simply a catch all term for all related amplifiers such as differential amplifier, summing amplifier, etc.?

2: Are there other kinds of amplifiers besides op-amp?

3: I have always been under the impression that an amplifier is used to amplify voltage. Can an amplifier also be used to amplify current?

4: The word 'feedback' simply suggests something that is returned to a machine, system, or process to improve output. I have seen in some circuits that a wire connects the output of the amplifier with one of its input and I presume it's called feedback. How would you explain this feedback and its use? Please keep it simple.
 

crutschow

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1: As I previously said an op amp is just an amplifier block with high gain and differential inputs. It's not of much use without additional external components to configure it to do what you want. It can be configured to be an inverting amp, non-inverting amp, summing amp, integrator, differentiator, etc., with a defined gain as determined by these additional components.

2: There are many other kinds of amps: audio amps, RF amps, microwave amps, etc. Op amps are just very common since they can be configured to do so many things.

3: Yes. An op amp can be configured to amplify small input currents to generate larger currents or an output voltage proportional to the input current (trans-impedance amp).

4: There is both positive and negative feedback. Positive feedback generally leads to amplifier oscillations or latchup so is not generally intentionally used. Negative feedback takes a sample of the signal from the output and applies it to the amplifier input such that it reduces (stabilizes) the amplifier gain and reduces distortion.

A simple example is an op amp configured as an inverting amplifier (below) with the (+) input grounded, input resistor (Rin) connected to the (-) input, and a negative feedback resistor (Rf) connected from the op amp output to the same (-) input. With that configuration the high gain of the op amp, will cause the op amp to always try to keep the (-) input very close to the same voltage as the (+) input (in this case the same potential. as ground). This means the current trough Rf must equal the negative of the current though Rin.

Think about why this is so. Suppose that the current from the output is slightly higher through Rf into the (-) junction then that through the input Rin. This will cause the (-) voltage to rise. The amp gain then causes the output voltage to drop and reducing the current through Rf until it matches the input current.

Since the two currents are equal then Vin/Rin = -Vout/Rf. Cross multiplying gives the value for the gain as Vout/Vin = -Rf/Rin (the minus means the gain is negative, it's an inverting amp). Notice that the closed-loop gain is determined by the value of Rf and Rin, not the op amp gain which is normally several magnitudes higher.


Inverting Amp.jpg
 
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colin55

Well-Known Member
Here are some diagrams showing the operation of an op-amp:
**broken link removed**

<mod edit: self promotion deleted>
 
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crutschow

Well-Known Member
Most Helpful Member
Here are some diagrams showing the operation of an op-amp:
**broken link removed**
That diagram is for an op amp connected as an open-loop comparator.
 
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