Why opamp is used

Technology Basics Resources. Commonly available op-amp IC. Internal circuit of IC Pin diagram. Op amp operational amplifier from Kausik das You can view the video tutorial on Operational Amplifier is here.

This article was first published on 17 July and was updated on 17 July Very informative. Reading your articles on various topics leads to refresh the fundas.

Really helpfull, gain should not have units though. Please enter your comment! Please enter your name here. You have entered an incorrect email address! What's New Electronicsforu. Good News! Most Popular DIYs. Condensed Water Atomiser For Air-conditioners. Electronics Components.

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It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. I've read in several books and papers the observation: "Op amps are the bread-and-butter of analog electronics", or " Although my experience is not broad enough either to concur or to refute that claim, it's certainly borne out in the circuits I have seen.

It makes me think I'm missing something fundamental, to explain why a component like this would be perhaps something like a "for" loop in programming or something, a fundamental pattern, that once available, finds pervasive application. What is it about the fundamental nature of analog electronics that makes an op amp the fulfillment of such a basic and versatile pattern? Op amps are pretty close to being ideal differential amplifiers.

So the real question is, what's so great about amplifiers? There are at least! First, the obvious -- amplifiers let you change the amplitude of a signal. If you have a small signal say, from a transducer , an amplifier lets you raise its voltage to a useful level. Amplifiers can also reduce the amplitude of a signal, which could be useful to fit it into the range of an ADC, for example.

Amplifiers can also buffer a signal. They present a high impedance on the input side and a low impedance on the output side. This allows a weak source signal to be delivered to a heavy load. Finally, negative feedback allows amplifiers to filter a signal. So-called active filters which use amplifiers are much more flexible and powerful than passive filters which use only resistors, capacitors, and inductors.

I should also mention oscillators , which are made using amplifiers with filtered positive feedback. Amplitude control, buffering, and filtering are three of the most common things you can do to analog signals. More generally, amplifiers can be used to implement many kinds of transfer functions , which are the basic mathematical descriptions of signal processing tasks.

Thus, amplifiers are all over the place. Why op amps in particular? As I said, op amps are essentially high-quality amplifiers. Their key characteristics are:. These characteristics mean that the behavior of the amplifier is almost entirely determined by the feedback circuit. Feedback is done with passive components like resistors, which are much better-behaved than transistors. Try simulating a simple common emitter amplifier across voltage and temperature -- it's not great.

With modern improvements in integrated circuits, op amps are cheap, high-performance, and readily available. Unless you need extreme performance high power, very high frequency there's not much reason to go with discrete transistor amplifiers anymore.

Fundamentally, as a signal gets processed through analog discrete elements, its amplitude—its voltage—drops. An op amp can buffer and boost an analog signal, ensuring it is readable or useful at the end. Incidentally, a for loop would be a counter. An op-amp itself might have input impedance in the 10's or 's of gigohms. An op-amp feedback circuit will likely have a lower input impedance, but the high input impedance of the op-amp allows this to be entirely set by the other components.

This means. Often only a few precision components are required in the feedback circuit to achieve precision performance from the overall circuit. Since the behavior of the circuit is controlled by the feedback circuit, the op-amp can be used with numerous different feedback elements to achieve different functions like amplification, differentiation, integration, logarithmic amplification, etc.

This may be the key reason that op-amps have such "pervasive application". With op-amp you can get non-exhaustive list! That's more than everything you will probably need for essential analog processing - and some of those things are neat for digital processing too.

As such, op-amps are both the bread and butter here. Also, you can easily get e. To pick out one particular electronic component and call that the "bread and butter" is silly, as is all these "most important" kind of statements. For example, count resistors in analog circuits, and I'm sure you'll find they outnumber opamps by a wide margin. Also, things change.

There was a time when vacuum tubes were the layman's silly "most important" or "bread and butter" component of analog electronics, then the transistor. You never need to use a opamp, but it can be the most efficient way to implement a circuit to a particular spec. After all, opamps are made from transistors, so it is possible to use a bunch of transistors with a few other components instead.

The attraction of opamps is that they embody a common and easily utilized building block. It is important to note that input impedance is not solely determined by the input DC resistance. Input capacitance can also influence circuit behavior, so that must be taken into consideration as well.

However, the output impedance typically has a small value, which determines the amount of current it can drive, and how well it can operate as a voltage buffer. An ideal op amp would have an infinite bandwidth BW , and would be able to maintain a high gain regardless of signal frequency.

Op amps with a higher BW have improved performance because they maintain higher gains at higher frequencies; however, this higher gain results in larger power consumption or increased cost. GBP is a constant value across the curve, and can be calculated with Equation 1 :. These are the major parameters to consider when selecting an operational amplifier in your design, but there are many other considerations that may influence your design, depending on the application and performance needs.

Other common parameters include input offset voltage, noise, quiescent current, and supply voltages. In an operational amplifier, negative feedback is implemented by feeding a portion of the output signal through an external feedback resistor and back to the inverting input see Figure 3. Negative feedback is used to stabilize the gain.

This is because the internal op amp components may vary substantially due to process shifts, temperature changes, voltage changes, and other factors. The closed-loop gain can be calculated with Equation 2 :. There are many advantages to using an operational amplifier.

Op amps have a broad range of usages, and as such are a key building block in many analog applications — including filter designs, voltage buffers, comparator circuits, and many others.

In addition, most companies provide simulation support, such as PSPICE models, for designers to validate their operational amplifier designs before building real designs. The limitations to using operational amplifiers include the fact they are analog circuits, and require a designer that understands analog fundamentals such as loading, frequency response, and stability. It is not uncommon to design a seemingly simple op amp circuit, only to turn it on and find that it is oscillating.

Due to some of the key parameters discussed earlier, the designer must understand how those parameters play into their design, which typically means the designer must have a moderate to high level of analog design experience.

There are several different op amp circuits, each differing in function. The most common topologies are described below. The most basic operational amplifier circuit is a voltage follower see Figure 4. This circuit does not generally require external components, and provides high input impedance and low output impedance, which makes it a useful buffer. Because the voltage input and output are equal, changes to the input produce equivalent changes to the output voltage.

The most common op amp used in electronic devices are voltage amplifiers, which increase the output voltage magnitude. Inverting and non-inverting configurations are the two most common amplifier configurations. Both of these topologies are closed-loop meaning that there is feedback from the output back to the input terminals , and thus voltage gain is set by a ratio of the two resistors.

In inverting operational amplifiers, the op amp forces the negative terminal to equal the positive terminal, which is commonly ground. In this configuration, the same current flows through R2 to the output. The current flowing from the negative terminal through R2 creates an inverted voltage polarity with respect to V IN. This is why these op amps are labeled with an inverting configuration. V OUT can be calculated with Equation 3 :.