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What is an Operational Amplifier?
An operational amplifier is also known as a short forms op-amp and op-amp is an amplifier with a DC-coupled high-gain electronic voltage. It has a differential input and is known for giving single-ended output.
An op-amp is known for producing an output potential in this configuration which is relative to the circuit ground. This output potential has been observed to be 100,000 times larger than the potential difference which is known to exist between the input terminals.
An operational amplifier has been originated from the analog computers which were used for performing various mathematical operations in frequency-dependent, linear and non-linear circuits. What makes this amplifier popular in the form of a building block in analog circuits is its versatility.
The characteristics of an operational amplifier circuit, bandwidth, input, output, etc. are determined by the external components by utilizing the negative feedback received. They have little dependence on the temperature of coefficients or the tolerance of engineering.
These are mostly used in electronic devices which comprise various industrial, scientific, and consumer devices. Most of the standard IC operational amplifiers cost a few cents while the integrated operational amps which have specifications mentioning special performance cost more.
These may either be packed in the form of components or utilized as elements of various complex hybrid circuits. An operations amplifier is a type of differential amplifier. It generally comprises three terminals including a low-impedance output and two high-impedance input ports.
In this, the inverting input is denoted by a minus sign whereas the non-inverting input utilizes a positive sign. While the inverting input is being denoted by using a minus sign, a positive sign denotes a non-inverting input.
These amplifiers are known to work for amplifying the voltage differential lying in between the inputs. This is mainly useful for a variety of analog functions which consists of power, control applications, and signal chain.
Operational amplifiers act as the basic building blocks of the analog electronic circuit. These may be considered linear devices having all the properties of a DC amplifier. The capacitors or external resistors may be used to these in various ways to use them as different amplifiers such as non-inverting amplifier, comparator, summing amplifier, differential amplifier, integrator, etc.
Types of Operational Amplifier
There are various types of operational amplifiers, let’s read further. The classification of the operational amplifier on the basis of gains is as follows. These are low gain amplifiers, medium gain amplifiers, and high gain amplifiers.
1. Low Gain Amplifiers
Low gain amplifiers are the ones that have low gain value and are used for the purpose of matching the impedance and as buffers.
2. Medium Gain Amplifiers
The amplifiers with the medium value intensity are defined as the medium gain amplifiers. These are the most commonly used amplifiers in the field of medicine. Also, they are used for recording the ECG waveforms and need the value of muscle potentials.
3. High Gain Amplifiers
The amplifiers with high intensity of gain are termed high gain amplifiers. These amplifiers are used for recording sensitive data such as recording the information of the brain signals.
Operational Amplifiers: Key Characteristics and Parameters
An operational amplifier has numerous characteristics and parameters which are as follows.
Open-Loop Gain: The open-loop gain in an operational amplifier may be defined as the measure of the gain that is achieved when no feedback is implemented in the circuit. This refers to the fact that the loop or the feedback path is open.
The requirement for an open-loop gain to be useful is that it should be extremely large except with voltage comparators. These comparators are known for comparing the input terminal voltages.
Voltage comparators are capable of driving output to negative or positive rails with small voltage differentials. In closed-loop configurations, the high open-loop gains are highly beneficial, the reason being their ability to stabilize the behavior of the circuit across process, temperature, and signal variations.
Input Impedance: One of the important characteristics of the operational amplifier is that it normally has a high input impedance. The input impedance is measured between the positive and negative input terminals with the ideal value being infinity which is known for minimizing the source loading.
The circuitry is arranged around the operational amplifier such that it may lead to a significant alteration of the effect of the input impedance for the source. This is why the feedback loop and the external components are required to be carefully configured.
It is crucial to know that the input impedance is not determined only by the input DC resistance. The input capacitance is known for influencing the circuit behavior therefore this must be taken into consideration.
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Output Impedance: The operational amplifier or op-amp is known for having zero output impedance. This typically has a little value that determines the current amount which it can drive along with how fluently the voltage buffer may be operated by it.
Frequency Response and Bandwidth: An ideal op-amp is known for having an infinite bandwidth or BW and is capable of maintaining high gain unaffected by the frequency of the signal. All the operational amplifiers possess a finite bandwidth which is normally known as the 3dB point.
In this, the gain starts rolling as the frequency increases and the amplifier gain decreases at a rate of 20dB/decade. The operational amplifier that has a higher bandwidth delivers better performance as it is known for maintaining high gains at high frequencies. This high gain requires huge power consumption and increased cost.
Gain Bandwidth Product (GBP): GBP or gain-bandwidth product is the product of an amplifier’s gain and bandwidth. It may be defined as a constant value present across the curve and is measured at the frequency point where the operational amplifier’s gain reaches unity.
It is considered useful as it facilitates the user to calculate the open-loop gain of the device at various frequencies. It is a measure of performance and usefulness; the operational amplifier with high GBP is useful in achieving quality performance at high frequencies.
These form the major parameters which must be considered when the op-amp is selected in the design. However, there are numerous considerations that are known for influencing the design as per the performance and application needs.
Some other important parameters comprise input offset voltage, supply voltages, noise, and quiescent current.
Negative Feedback and Closed-Loop Gain: When it comes to an operational amplifier, negative feedback is being implemented. This is done by feeding a part of the output signal via an external feedback resistor and receiving it back to the inverting input.
To stabilize the gain, negative feedback is being used. The closed-loop gain is being determined by using it through external feedback components which have high accuracy in comparison to the op amp’s internal components.
This is so because the operational amplifier’s internal components are known for having substantial variance as a result of temperature changes, process shifts, voltage changes, and various other factors.
Advantages of Operational Amplifier
Various advantages of operational amplifiers are as follows. These are usually present in the form of an IC and are available easily with numerous performance levels which are selectable. They can be used to fulfill various needs of an application.
It has many uses and acts as an important building block in analog applications which comprises voltage buffers, comparator circuits, filter designs, and others. Additionally, there are many companies that are known for providing simulation support.
Limitations of Operational Amplifiers
The operational amplifiers have numerous limitations as well. These are the analog circuits that need a designer who has a proper understanding of the analog fundamentals. These fundamentals include frequency response, stability, and loading. It is very common to design a simple operational amplifier circuit that oscillates when turned on.
As discussed earlier, according to the key parameters the designer is required to understand how the parameters play into design. This means that the designer is required to have a moderate to the high-level experience of the analog design. These were the limitations of operational amplifiers.
Operational Amplifier Configuration Topologies
There are various operational amplifiers available in the market which are different in the functions they perform. Let’s read about the common operational amplifier configuration topologies that are available.
Voltage Follower: Voltage follower is the most used basic operational amplifier circuit. This circuit mostly does not require external components and provides both high input impedance and low output impedance. This is what makes it the most useful buffer as the voltage input and output are equal and the changes to input produce are equal to the output voltage.
The most commonly used operational amplifier in electronic devices is a voltage amplifier which increases the output voltage magnitude. Both inverting and non-inverting configurations are the most commonly used amplifier configurations.
These topologies are closed-loop which means that there is feedback being received from the output back to the input terminals. Therefore, the voltage gain is being set by a ratio of the two resistors.
Inverting Operational Amplifier: It has been observed that the operational amplifier forces the negative terminal to equal the positive terminal which is a common ground when it comes to an inverting operational amplifier. The operational amplifiers are labeled with the help of an inverting configuration.
Non-Inverting Operational Amplifier: The input signal in the non-inverting amplifier circuit from the circuit is joined with the non-inverting positive terminal. It has been observed that the operational amplifier forces the negative inverting terminal voltage to equal the input voltage. This in turn creates a current flow via the feedback resistors.
Here, the output voltage is always seen in phase with the input voltage, this is why the topology is called the non-inverting. It is to be noted that the voltage gain always more than 1 when it comes to a non-inverting amplifier.
Voltage Comparator: The operational amplifier voltage comparator is known for comparing the voltage inputs and driving the output to the supply rail of the one with higher input. In this, the configuration is an open-loop operation as there is the absence of any feedback. Here, the voltage comparators own the benefit of operating at a much faster rate as compared to the closed-loop topologies.
Operational Amplifier Applications
Specifically saying, the operational amplifiers are the versatile circuit blocks. These blocks find the applications in a host of various circuits with high gain attributes, low output impedance, high input impedance, and different input. This allows them to deliver a high level of performance by utilizing minimum components.
The operational amplifiers may be used in various circuits and applications by using both positive and negative feedback around its chip. These are known for performing different types of functions as filters, integrators, oscillators, amplifiers, etc.
There are numerous operational amplifier circuits that are capable of covering almost all the required analog functions. The op-amp as a result of this has become the workhouse of the analog electronic designer.
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The operational amplifier applications are many as they may be used in various applications and circuits. It is considered an almost perfect amplifier because of its need in many applications; its high gain, differential input, and high input impedance make it ideal.
How to Choose the Best Operational Amplifier?
You need to follow these important steps while selecting the best operational amplifier. These are as follows. Firstly, choose the operational amplifier which supports the expecting range of your operating voltage. This information may be easily obtained by looking at the amplifier’s power supply voltages.
The amplifier may be in a position to support both the negative and positive supply. The negative supply is useful in case the output is needed for supporting the negative voltages. Now, the second step is to consider the GBP of the amplifier.
In case, the application you are using requires high performance, reduced distortion, or has a need to support the high frequencies, then an operational amplifier with higher GBPs may be considered.
While selecting an op-amp, its power consumption must also be checked. There are certain applications present that are capable of operating with low power. The power requirements may be easily obtained from the part’s datasheet.
These requirements are generally listed as the power consumption and supply current. The other way of estimating the power consumption is by the production of the supply voltage and supply current. Usually, the operational amplifiers that have lower supply currents possess low GBP and are known for corresponding with lower circuit performance.
The designer must pay special attention to the input offset voltage of the amplifier, in case the applications that you are using require a high rate of accuracy. This is required as this voltage is responsible for the offset in the amplifier’s output voltage.
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