What is an operational amplifier (op-amp)?

An operational amplifier also called op amp is an integrated circuit or analog circuit that takes input as a differential voltage and produces output as a single-ended voltage. It is an IC that can amplify weak electric signals.
An op amp has one output pin and two input pins. The basic role of an opamp is to amplify the voltage difference between the two input voltages. It is also used in filtering or to perform mathematical operations or in signal conditioning.

Construction of an operational amplifier

A basic Op-amp has 3-terminals consisting of two inputs and one output. It also has pins for power connections. The input pins have two high-impedance while the output pins have low impedance. They are mostly made of transistors and resistors. The inputs are inverting and non inverting types. The inverting input has a negative sign while the non-inverting input is marked with a positive sign. The output port can do both i.e. sink and source voltage or current.

The internal schematic circuit diagram of a common mode operational amplifier is shown below this:

Parameter and Ideal Characteristics

Аn ор-аmр has unlimited functions and is the basis for the edge architecture of analog-to-digital and offline line systems. The ideal and real characteristics of op amp are given below:

• Open Loop Gain, (A_vo)- Gain of the op-amp without positive or negative feedback is the open loop gain. An ideal op amp has infinite open loop gain but real values range from 20,000 to 200,000. An opamps main function is to amplify the input signal, the amplification will be more if it has more loop gain.
• Input impedance, (Z_IN)- The ratio of input voltage to input current is the input impedance. An ideal op amp has infinite input impedance to prevent any current flow from the source to the amplifier's input. But there is input leakage currents of some micro-amperes in real op-amps.
• Output impedance, (Z_OUT)- The output impedance of the ideal op amp is zero. It acts as a perfect voltage source with no internal resistance. Real op-amps have output impedances of about 100 Ω to 20 kΩ.
• Bandwidth- Bandwidth is the frequency range for which the voltage gain is above 70.7% of maximum output. An ideal op amp has an infinite frequency response, it can amplify any frequency from DC to AC, hence it has an infinite bandwidth. But real op-amps have the limited bandwidth that is measured as Gain-Bandwidth product (GB). Gain-Bandwidth product is equal to the frequency where the amplifier's gain becomes unity.
• Offset Voltage, (V_IO) - Ideally, if the voltage difference between two inputs of op amp is zero, the op amps output must be zero. However real op-amps have some amount of output offset voltage.

Frequency response and Bandwidth

Frequency response allow us to study amplifier at different frequency. In small signal analysis or ac analysis of amplifier we generally stick to a particular frequency. The frequency at which we analyze the amplifier is selected in such a way that gain of amplifier remain constant. At this frequency, analysis is done by ignoring the effect of the capacitive elements and only resistive elements are considered.

In frequency response, we study the effect of various capacitive elements such as

• Effect of blocking , coupling and bypass capacitor (these capacitor have large value and comes into play at low frequency).
• Effect of transistor capacitance or parasitic capacitance (these capacitance are small and comes into play at high frequency).

In general frequency response gives you an idea about how gain changes with frequency.

Types of op amps

There are any types of op amps available, soe of the are given below:

Vоltаge fоllоwer

By connecting the output of the operational amplifier directly to the inverting terminal without the use of any passive elements the op-amp becomes a voltage follower. Voltage follower is mostly used as a buffer in many applications. Below is a general circuit diagram for voltage follower op-amp:

Inverting operational amplifier

The term “inverting amplifier” implies two different functions.

An inverter changes a signal such that an positive input produces a negative output and vice versa. (In digital circuits an inverter changes a 1 to a 0 and a 0 to a 1. An amplifier increases one or more of the input signal’s parameters, voltage, current, or power.

So, for an inverting voltage amplifier a small positive input voltage the output would be a larger negative output voltage.

For an AC signal the output would be 180° out of phase with the input.

$V_{out}=-\left(\frac{R_2}{R_1}\right)V_{in}$Below is a general circuit diagram for Inverting operational amplifier:

Comparator circuit

The comparator circuit compares the two voltages with the output of one or auto-zero to indicate that is more. Comparator circuit comparisons are often used, as an instance, to test whether inputs have reached a predetermined variable.

Rail-to-rail

In analog signals, a “rail” is a signal boundary that a component has to work within. Opamps often require equal and opposite voltage supplies for example in a dual-supply or dual-voltage op amp. Hence, here rail implies the voltage levels of an op amp. An upper rail is the voltage output to the highest voltage level. Signal sources are often connected to the positive or negative supply rail. Rail-to-rail op amps means that the signal swings completely (positive and negative) upto supply voltage. 

Operational amplifiers need rail-to-rail input capability to match both signal sources with one device. Rail-to-rail op amps enable us to function at lower supply voltages, swing closer to the extreme values, and provide a more dynamic range of output.

Common Mistakes

Саreful оn thаt роint- Due to the requirements within the ор-amp, its unique voltage tends to decrease due to the increased frequency of entry. Many oр-amp response curves are available from the manufacturer.

Context and Applications

Oр-аmр has countless programs and forms the largest blockchain architecture for direct and indirect simulation formats. There are many benefits to using an effective operational amplifier. Active operational amplifiers are always integrated with IС form, and have a high-pass degree of flexibility, with a variety of operating modes to choose from to meet the requirements of each system. Op amp has a wide range of uses, and as such is the key to building on many analog programs - including filter formations, electric baths, composite structures, and structures. In addition, the it provides simulation guidelines so that designers can verify their amplifier design before creating the actual design.

In each of the expert exams for undergraduate and graduate publications, this topic is huge and is mainly used for:

• Bachelor of Technology in the electrical and electronic department
• Bachelor of Science Physics
• Master of Science Physics

Related Concepts

• Audio Frequency Amplifier
• Intermediate Frequency Amplifiers

Practice Problems

Q1 What is bandwidth for op-amp_______:

(a) -3.5db

(b) -3.2db

(c) 3db

(d) -3.db

Correct option: (d)

Explanation: Operational amplifiers have a finite bandwidth -3db.

Q2 How many type of op-amp are available on basis of power supply?

(a) One

(b) Two

(c) Three

(d) Four

Correct option: (b)

Explanation: Two types of op-amps (1) single power supply type and (2) dual power supply type. 

Q3 Op-amp is a _________ type amplifier.

(a) Voltage

(b) Current

(c) Power

(d) None of these

Correct option: (a)

Explanation: Op-amp is a voltage-type amplifier. The operating amplifier (op-amp) is an analog circuit block that takes in a different voltage input and produces a single-ended voltage output.

Q4: Op-amp has _______ input impedence.

(a) low

(b) high

(c) high-low

(d) low-high

Correct option: (b)

Explanation: Op-amp has a high advantage with very high impedance input. That is, the output is the difference between input, a maximum number of times and input does not accept any current.

Q5 Op-amp operation is based on _________ performance:

(a) Logical

(b) Arithmetic

(c) Both

(d) None of these

Correct option: (c)

Explanation: It can perform basic mathematical operations including addition, subtraction, multiplication, and division.