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Salient features of operational amplifier as comparator

The acronym of the term Op-Amp is an operational amplifier and it is a one type solid state integrated circuit. The op-amp is the basic building blocks of analog electronic circuits that perform a various types of analog signal processing tasks. Operational amplifiers use external feedback to control its functions and these are the multipurpose devices in all electronic devices. Op-Amp has two inputs and one output termed as inverting and noninverting. IC op amp is the most common op-amp used in various electronic circuits. The main function of an op-amp is to amplify AC and DC signals and also for mathematical operations like addition, multiplication, subtraction, etc.

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Op-Amp Basics: What Is An Operational Amplifier?


In this tutorial, we will learn about one of the important circuits in analog circuit design: A Differential Amplifier. It is essentially an electronic amplifier, which has two inputs and amplifies the difference between those two inputs.

We will see the working of a Differential Amplifier, calculate its gain and CMRR, list out some important characteristics and also see an example and an application. The Differential Pair or Differential Amplifier configuration is one of the most widely used building blocks in analog integrated-circuit design. It is the input stage of every Operational Amplifier. A Difference Amplifier or a Differential Amplifier amplifies the difference between the two input signals.

An operational amplifier is a difference amplifier; it has an inverting input and a non-inverting input. But the open loop voltage gain of an operational amplifier is too high ideally infinite to be used without a feedback connection.

So, a practical differential amplifier uses a negative feedback to control the voltage gain of the amplifier. The following image shows a simple Differential Amplifier using an Op Amp. If you observe the above circuit of the difference amplifier, it is a combination of both the Inverting Amplifier and the Non-Inverting Amplifier.

So, to calculate the output voltage of a Differential Amplifier, we will use both the Inverting and Non-Inverting outputs and add them together. To get the final V OUT value, we have to add these values. The above equation looks complex. Hence, it is Differential Amplifier. Let us now calculate the output voltage by determining the current at the Inverting Input of the Op Amp. Let us assume the following circuit for a Differential Amplifier.

We already calculated this in the previous derivation using the voltage divider rule. The value is given by:. So, the current entering the Inverting Terminal I 1 is same as the current leaving the terminal I 2. Actually, instead of this we have to consider the ratios i. The gain of a difference amplifier is the ratio of the output signal and the difference of the input signals applied. From the previous calculations, we have the output voltage V OUT as. Due to this, the Differential Amplifier is often used at the input stage of a system to strip the DC or the Common-Mode noise from the input.

All these calculations are true if and only if the Resistances form the Balanced Bridge Condition. Since the output of a practical difference amplifier depends upon the ratio of the input resistances, if these resistor ratios are not exactly equal, the common mode voltage V CM will not be completely cancelled. Because it is practically impossible to match resistor ratios perfectly, there is likely to be some common mode voltage.

With the common mode input voltage present, the output voltage of the differential amplifier is given as,. Hence, the CMRR is infinite. A Wheatstone Bridge Differential Amplifier circuit design is as shown in the following image. This circuit behaves like a Differential Voltage Comparator. By connecting one input to a fixed voltage and the other to a thermistor or a light-dependent resistor , the differential amplifier circuit detects high or low levels of temperature or intensity of light as the output voltage becomes a linear function of the changes in the active leg of the resistive bridge network.

A Wheatstone Bridge Differential Amplifier can also be used to find the unknown resistance in the resistive bridge network, by comparing the input voltages across the resistors. The voltage V 2 is determined by the variable resistor V R1. The resistors R 1 and R 2 act as a potential divider network.

A fixed reference voltage is applied to the inverting input, through R 1 and R 2. The same circuit can be modified to detect variations in temperature, simply by replacing the LDR with a Thermistor. By interchanging the positions of LDR and V R1 , the circuit can be made to detect dark or light or heat or cold in case of a thermistor. The differential gain of the amplifier is and the value of CMRR is.

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Operational Amplifiers

In most of the previous operational amplifier tutorials , the circuits had a feedback loop to the inverting input. This design is the most common because it provides indeed stability and avoids undesirable saturating effects and, it is also common to call it the linear mode. On the other hand, when no feedback is applied to the inverting input, the op-amp is said to work in the non-linear regime , we can also say in an open-loop configuration. Comparators are specific op-amps circuits that are meant to work in a non-linear mode and can be used as simple logic gates. A presentation of the circuit along with the basics about comparators is given in the first section. We show that being able to translate this value is important in order to properly design level detectors.

A voltage gain of 5 means that the output voltage, VOUT, is five times bigger than the input voltage, VIN. There are three main categories of amplifiers: •.

Comparator Circuit


In principle, any high-gain amplifier can be used to perform this simple decision. For example, for use with digital circuitry, many comparators have latched outputs, and all are designed to have output levels compatible with digital voltage-level specifications. There are some more differences of importance to designers—they will be discussed here. Amplifiers should be considered for use as comparators in applications where low offset and drift, and low bias current, are needed—combined with low cost. On the other hand, there are many designs where an amplifier could not be considered as a comparator because of its lengthy recovery time from output saturation, its long propagation delay, and the inconvenience of making its output compatible with digital logic. Additionally, dynamic stability is a concern. However, there are cost and performance benefits in using amplifiers as comparators—if their similarities and differences are clearly understood, and the application can tolerate the generally slower speed of amplifiers. No one can claim that an amplifier will serve as a drop-in replacement for a comparator in all cases—but for slow-speed situations requiring highly precise comparison, the performance of some newer amplifiers cannot be matched by that of comparators having greater noise and offset. In addition, there can be savings in cost or valuable printed-circuit-board PCB area in applications where a dual op amp could be used instead of an op amp and a comparator—or in a design where three of the four amplifiers in a quad package are already committed, and two dc or slowly varying signals must be compared.

OPAMP Comparators

salient features of operational amplifier as comparator

An op-amp is a multi-stage , direct coupled, high gain negative feedback amplifier that has one or more differential amplifiers and its concluded with a level translator and an output stage. A voltage-shunt feedback is provided in an op-amp to obtain a stabilized voltage gain. The main use of an op-amp is to amplify ac and dc input signals and was initially used for basic mathematical operations such as addition, subtraction, multiplication, differentiation and integration. It is also designed in such a way that the external characteristics can be changed with the addition of external components like capacitors and resistors. Thus it can act as a complete amplifier with various characteristics.

Operational amplifiers are the basic building blocks of Analogue electronic circuits. They are linear devices with all properties of a DC amplifier.

Operational Amplifiers


Amplifiers and Comparators Minimize menu. Please log in to show your saved searches. ST's operational amplifier portfolio provides a unique choice of high performance, low power, precision op amps and tiny packages. It addresses voltages from 1. Get instant access for free to our recorded webinar, covering:. Go to the webinar now.

Operational amplifier

Hysteresis is one of those concepts with a fancy name and a deceptively simple meaning. Many physical systems, including plenty of electronic components, exhibit hysteresis. In essence, the state of the system depends upon events that occurred in the system at all previous points in time. Although this might sound like an odd occurrence, it is common and very useful in a variety of electronic circuits. You can take advantage of hysteresis in analog circuits and even build hysteresis into your circuits using feedback and saturation, providing plenty of useful functionality. Hysteresis phenomenon occurs when ferromagnetic materials are magnetized in one direction; even when the imposed magnetizing field is removed, ferromagnetic materials will not relax back to zero magnetization. Because the material can only be driven back to zero with a field in the opposite direction, there is a lack of retraceability known as hysteresis. When this occurs, applying an alternating magnetic field will yield a hysteresis loop.

Voltage comparators compare the input terminal voltages. Another important characteristic of op amps is that they generally have high input impedance.

The Web This site. The output of an op amp can swing positive and negative to a maximum voltage close to the supply rail potentials. Using the maximum open loop gain in this way can be useful when either dealing with extremely small and low frequency or DC inputs in instrumentation or medical applications, or for comparing two voltages, using the op amp as a comparator. In this mode the output will go to either a maximum high or minimum low level, depending on whether one input is just a few micro volts higher or lower than a reference voltage applied to the other input.

An operational amplifier or op-amp is simply a linear Integrated Circuit IC having multiple-terminals. The op-amp can be considered to be a voltage amplifying device that is designed to be used with external feedback components such as resistors and capacitors between its output and input terminals. It is a high-gain electronic voltage amplifier with a differential input and usually a single-ended output. Op-amps are among the most widely used electronic devices today as they are used in a vast array of consumer, industrial and scientific devices. An op-amp has countless applications and forms the basic building block of linear and non-linear analogue systems. Some of the types of op-amp include:.

In electronics, the open-loop voltage gain of the actual operational amplifier is very large, which can be seen a differential amplifier with infinite open loop gain, infinite input resistance and zero output resistance. In addition, it has positive and negative inputs which allow circuits that use feedback to achieve a wide range of functions.

This lab session is intended to familiarize the students with some of the basic characteristics and applications of operational amplifiers op amps. Some of the most widely used applications will be tested and characterized. Also the students are encouraged to investigate any discrepancy between test results and the results that might be expected from theoretical analysis. Operational amplifiers are very popular integrated circuits that are available from various manufacturers to cover a wide range of operations and speed. In spite of the differences between various op amps available for different applications, they have many common properties. For example, op amps usually have a differential input with each input exhibits very high input impedance.

An operational amplifier op-amp is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. Operational amplifiers had their origins in analog computers , where they were used to do mathematical operations in many linear, non-linear and frequency-dependent circuits. Characteristics of a circuit using an op-amp are set by external components with little dependence on temperature changes or manufacturing variations in the op-amp itself, which makes op-amps popular building blocks for circuit design. Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices.




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