While dealing with electrical circuits, sometimes it is required to amplify the signal to a certain amount. This amplification can be performed by a device named an operational Amplifier which has a certain gain associated with it. In this article, we will study the op-amp and try to understand the working principle behind an op-amp.

We will also study the applications of op-amp and use certain examples to understand the applications better. Later we will study the advantages and disadvantages of op-amp and discuss the possible future trends in an op-amp. The article will conclude with some frequently asked questions that readers can refer to.

What is Op-Amp?

The term op-amp stands for operational amplifier. It can be described as a multistage amplifier that has a gain value associated with it. An operational amplifier is used for different purposes like amplification, subtraction, differentiation, addition, integration, etc. The internal circuitry of an op-amp is complicated since it includes transistors, FETs, and resistors to form a multistage amplifier. Next, we will go through the Working of the Op Amp.

Working Principle of Op Amp

Given Below is the circuit diagram of the Operational Amplifier

A simple amplifier consists of two input terminals and one output terminals as shown. Let us see how the op-amp works when an input is fed to the terminal of the op-amp.

• The input terminals of the op-amp are fed with two inputs. One input is fed at the inverting and another at the non-inverting terminal. This input is known as differential input voltage.
• After the input is applied, the ideal op-amp performs the task of amplification. In general, the open loop gain associated with an ideal op-amp is very high. Therefore, when an input is applied to the op-amp, a large output value is produced. The equation used for calculating the gain is given by.

V_out= A (V₁ – V₂)

A=Gain of the op-amp

V_out is the output voltage,

V₁ is the voltage at the non-inverting terminal,

V₂ is the voltage at the inverting terminal.

Applications of Op Amp

Let us study the applications of the op-amp:

• Op Amp As Signal Amplifier
• Op Amp As Filters
• Op Amp As Voltage Comparators
• Op Amp As Oscillators
• Op Amp As Differentiator
• Op Amp As Integrator
• Op Amp As Voltage to Current Converter
• Op Amp As Current to Voltage Converter
• Op Amp As Logarithmic Amplifier
• Op Amp As Half Wave Rectifier
• Op Amp As Peak Detector
• Op Amp As Non-Inverting Amplifiers
• Op Amp As Inverting Amplifiers
• Op Amp As Phase Shifter
• Op Amp As Scale Changer
• Op Amp As Adder or Summing Amplifier

Op Amp As Signal Amplifier

Op-amps are used for Signal amplification. Every op-amp has a certain gain associated with it and the output signal generated is the input signal multiplied by the gain of the multiplier. This is generally used in applications that involve weak signals which need to be amplified for different purposes. The input is fed to the two input terminals of the op-amp and is amplified.

Op Amp As Filters

Op-amps are used in filters. They are used to implement filters such as low-pass, high-pass, band-pass, and band-stop filters. The particular characteristics that make op-amps useful in filters are their high gain, high input impedance, and low output impedance characteristics. These filters are then used to block and pass certain frequencies depending on the requirements. L at the circuit used in this conversion with a mathematical formula.

Op-amp in Low Pass Filter

Gain(A_v)= V_out/ V_in

Op Amp As Voltage Comparators

Op-amps are used in comparators for comparing the input voltages. The input voltages to be compared are fed at the inverting and non-inverting terminal of the op-amp and a digital output is generated. This is useful in appliances like threshold detection, window comparators, and zero-crossing detectors in control systems, oscillators, and sensor interfaces. L at the circuit used in this conversion with a mathematical formula.

Voltage Comparator

feedback fraction(β)= R₁/(R₁+R₂)

Op Amp As Oscillators

Op-amps are used in making oscillators. The oscillator performs oscillations at a periodic interval to generate waveforms like sine waves, square waves, and triangular waves which are periodic. These oscillators are used in devices that need to keep track of periodic waveforms like clock generators, and audio oscillators. L at the circuit used in this conversion with a mathematical formula.

Op-amp oscillator circuit

RC frequency(f)= 1/2????RC

Op Amp As Differentiator

Op-amps are used largely in Integrator and Differentiator Circuits. The differentiator circuits as the name suggests generate a voltage proportional to the derivative of the input voltage fed to the op-amp. These circuits are very useful for signal processing and generating all the required signals. Look at the circuit used in this conversion with a mathematical formula.

Differentiator Circuit

V₀ = -dV_i/dt

where V_o is the output voltage, and, V_i is the input voltage

Op Amp As Integrator

Op-amps are used largely in Integrator and Differentiator Circuits. The integrator circuits as the name suggests generate a voltage proportional to the integral of the input voltage fed to the op-amp These circuits are very useful for signal processing and are used for different purposes. Look at the circuit used in this conversion with a mathematical formula.

Integrator circuit

V₀ = −1/RC ∫V_t dt

where V_o is the output voltage,

R is resistance,

C is the capacitance

Op Amp As Voltage to Current Converter

Op Amps are used as voltage-to-current converters where they can change the input voltage to generate current. This is done by applying a feedback circuit to the op-amp using certain resistances and current sources. Note that one popular op-amp used for voltage-current conversion is IC LM741 which generates enough current. Look at the circuit used in this conversion with a mathematical formula.

Voltage to Current CoVoltage to Current Converternverter

V_in = V_D + V_F ∴ V_in = I_L × R

∴ I_L = V_in/ R

Op Amp As Current to Voltage Converter

Op Amps are used as Current to Voltage Converter where the input current is used to generate the voltage. A feedback circuit made up of resistors and current sources, is used for generating the voltage when input is fed at the inverting terminal of the op-amp. The non-inverting terminal is usually grounded as shown below. Look at the circuit used in this conversion with a mathematical formula.

Current to Voltage Converter

(V_out – V_–)/R_f = I_p +I_–

∴ V_out =I_pR_f

Op Amp As Logarithmic Amplifier

Op Amp is used as Logarithmic a Amplifier. As the name suggests, logarithmic amplifiers are devices made using op-amps that perform mathematical tasks like calculating the logarithm and anti-logarithm values along with the amplification of the signal. The output generated in such devices is proportional to the logarithm of the applied input. Look at the circuit used in this conversion with a mathematical formula.

Logarithmic amplifier

V₀= -nV_T ln(V_i/R₁.I_s)

where V_o is the output voltage, and

V_i is the input voltage

Op Amp As Half Wave Rectifier

Op Amps are used as a Halfwave Rectifier. Rectifiers are devices that convert the AC input fed to them into DC output. The term ‘half-wave’ is used to indicate that this type of rectifier only generates positive half cycles for half the cycle and generates zero output for the remaining half cycles. Another type rectifiers are full-wave rectifiers that can covert AC input to DC output for full cycles. Look at the circuit used in this conversion with a mathematical formula.

Half wave rectifiers

V₀ = -(R_f/R₁).V₁

where, V_o is output voltage, and

V₁ is input voltage

Op Amp As Peak Detector

Op Amps are used as a Peak Detector for measuring a certain peak in the input signal. While dealing with signals, we often feel the need to measure the maximum or the peak value of a signal, and an op-amp can be used to solve this problem. This is usually done by measuring the threshold voltage and changing the diode bias according to block or pass the current. Look at the circuit used in this conversion with a mathematical formula. Look at the circuit used in this conversion with a mathematical formula.

Peak Detector

V₀= V_in -IR_f

where V₀ is the output voltage, and

V_in is the input voltage

Op Amp As Non-Inverting Amplifiers

Till now, we have seen that operational amplifiers are used as amplifiers and this can be done in mainly two configurations. One of which is a non-inverting amplifier. The important thing about this configuration is that the input voltage signal is applied directly to the non-inverting terminal of the op-amp. Since the signal is fed to the non-inverting terminal, the mathematical calculation shows that it results in a positive gain with an “in-phase” output signal. Look at the circuit used in this conversion with a mathematical formula.

Non-Inverting Amplifier

Gain(A_V) = 1+R_F/R₂

Op Amp As Inverting Amplifiers

Another configuration of using op-amp as an amplifier is inverting amplifier configuration. The important thing about this configuration is that the input voltage signal is applied directly to the inverting terminal of the op-amp. Since the signal is fed to the inverting terminal, the mathematical calculation shows that it results in a negative gain with an “out-of-phase” output signal. Look at the circuit used in this conversion with a mathematical formula.

Inverting Amplifiers

Gain(A_v) = -R_F/R_in

Op Amp As Phase Shifter

The term phase shifter is used for a device that can change the phase of the signal without changing the original amplitude of the signal. These circuits are usually designed using resistors, capacitors, and operational amplifiers. The phase of the signal is controlled by changing the resistance value of the programmable resistor. Look at the circuit used in this conversion with a mathematical formula.

Op-amp Phase Shifters

Phase Shift= π-2tan^-1(2πfRC)

where f represents the signal frequency.

R represents circuit resistance.

C represents circuit capacitance.

Op Amp As Scale Changer

An operational amplifier can also be used as a scale changer for comparatively small signals. It is used as a scale changer in inverting as well as non-inverting amplifiers. Here is a circuit for understanding how is op-amp used as a scale changer. If you carefully observe, you will see that the non-inverting terminal is grounded and the signal is fed to the inverting terminal with a resistance value of R, this results in a negative feedback system.

Op-amp as a Scale Changer

Op Amp As Adder or Summing Amplifier

The name “Summing Amplifier” is used since op-amps can be used to add two or more input voltages and generate a single output from it. It is important to note that input voltages are applied to the inverting terminal of the op-amp while the non-inverting terminal is grounded. The below circuit shows op-amp as an adder. Look at the circuit used in this conversion with a mathematical formula that shows that the output voltage is proportional to the sum of input voltages.

Summing Amplifier

V_out = -(R_f/R₁ .V₁ + R_f/R₂ .V₂ + R_f/R₃ .V₃)

Examples of Op Amp

Let us study the examples of the op-amp

• One important example of op-amp used in signal amplification is its use in audio amplification. Devices like home speakers need to amplify the input signal therefore, they use op-amps to amplify the amplitude of the signal in the smartphone or a DVD player resulting in loud music or audio signals. Op-amps can also be used in other amplification devices.
• Sometimes, instead of needing one signal, we can require a mixture of two or more than two signals. An Audio Mixer is a device that uses the summing action of an operational amplifier to generate a mixed signal. In recording stations, the signal voices from microphones, speakers, and instruments are combined to generate one signal which is a mixed output.
• Op-amps are used in making filters for example Active Low-Pass Filter. Active Low-Pass Filters are devices that are used to select the signals greater than a particular frequency and then block them from passing. Car stereo systems use these active Low-Pass Filters made up of operational amplifiers to attenuate certain noises.
• Op-amps are used in signal generation as a part of oscillators. Devices like electronic musical instruments use oscillator circuits to generate signals which are called notes. Operational amplifiers are used in these oscillators to produce waveforms such as sine waves, square waves, and sawtooth which can result in great musical notes.
• The use of Op-amps as a comparator can be seen in the Audio Level Meter to measure the maximum possible values of audio signals. By designing an operational amplifier with the desired gain, we can detect the level at which the peak of the signal has been reached. This is how op-amps are used as peak detectors.

Advantages of Op Amp

Let us study the advantages of the op-amp

• The compactness of op-amp is a very beneficial characteristic of op-amp since it allows integration of op-amp in larger circuits.
• Op-amps display a wide range of features which makes them a versatile device. They are used as amplifiers, comparators, and filters in analog engineering.
• Op-amps are simple to use and can be easily used in a circuit. In case an op-amp is damaged, it can be easily replaced without major changes required.
• Op-amps are cheap and pocket-friendly devices. This makes them the best choice for small-scale projects.
• Op-amps can be easily used in simulation circuits since they can be easily programmed to create circuits at a professional level.

Disadvantages of Op Amp

Let us study the disadvantages of the op-amp

• As the level of the circuit increases, it becomes difficult to implement the circuit. A good understanding of the concepts is required to create these complex circuits.
• The need for symmetrical power distribution across the input terminals is a major requirement for op-amps that can limit the use of op-amps in some applications.
• The op-amps are useful only for low-frequency appliances since they don’t have a good frequency response at high frequencies.
• Op-amps can’t handle high power since they can get destroyed due to the high power. Therefore, they are not suitable for h appliances.
• Op-amps have a slow response time which can result in a lag. This can be a major flaw for appliances that require fast switching actions.

Future Trends

With an advancement in technology, it is evident that there will be developments in operational amplifiers. These developments can be expected regarding the op-amp design, its performance, efficiency, and reliability. With the integration technology, it is expected that the future op-amps can be integrated onto a single chip to obtain a miniaturized version that can use the available space efficiently. Other developments in the op-amp can be seen in terms of reducing the power consumption of the op-amp, this can also result in environmentally sustainable devices that can reduce the electronic waste produced. This is how developments can be expected in op-amp in the coming time.

Conclusion

We have seen how op-amps form an integral part of electrical engineering. The ability of op-amps to amplify the input signal is utilized in different appliances like amplifiers, filters, and comparators. It is necessary to understand the working principle of op-amps to design the op-amp depending on the needs of your circuit. Despite the various advantages offered by op-amps, there are certain limitations associated with op-amps which have been discussed in the article. Readers are advised to refer to the frequently asked questions in case of any doubt.

Applications of Op Amp – FAQs

What are the two types of op-amps?

Op-amps can be divided into two categories namely Inverting op amp and Non-inverting op amp.

What is the input and output resistance of an op-amp?

The op-amp has an infinite input resistance and zero output resistance to ensure there is no change in output due to a change in load current.

What is an ideal operational amplifier?

An ideal operational amplifier has infinite open-loop gain, infinite input impedance, zero output impedance, infinite bandwidth, zero offset voltage, and zero noise which is not present in a practical op-amp.