What is Operational Amplifier (Op Amp): Its Circuit, Types and Applications

What is an Op Amp?

The operational amplifier, often referred to as Op Amp, is a linear Integrated Circuit (IC) with multiple terminals. Op Amps are vital components in electronic systems, used to amplify voltage differences between two inputs. They are designed to work with capacitors and resistors connected between their input and output terminals. Values and placement of resistors and capacitors affect its mode of operation. Widely utilized across consumer electronics, industrial equipment, and scientific instruments, op amps play a fundamental role in various electronic devices.

Op Amp Circuit Construction

An operational amplifier features five terminals, namely the positive power supply, negative power supply (GND), noninverting input, inverting input, and output. These terminals are commonly labeled, as shown in Figure 1.

Figure 1: Block Diagram of Op Amp

Where

V_CC, V_DD: Positive Power Supply

V_EE, V_SS: Negative Power Supply

V_IN(+): Non-Inverting Input

V_IN(-): Inverting Input

V_OUT : Output

Within the opamp circuit, it is ideal to have infinite resistance between two input terminals and zero resistance at the output side. Practically, the resistance between inverting and non-inverting terminals is very high. On the output side, output resistance is quite low but not zero.

Op Amp Operation

The operational amplifier amplifies the voltage difference between its noninverting (IN(+)) and inverting (IN(-)) inputs. The below equation describes the output voltage, indicating that it is in phase with V_IN(+) and in the opposite phase to V_IN(-).

Vout=A(Vin(+)-Vin(-))

Where A is the open loop gain of the amplifier.

In a linear operational amplifier, the output signal is determined by the amplification factor, referred to as the amplifier’s gain (A), multiplied by the input signal value.

Op Amp Parameters

• The open loop gain of an operational amplifier refers to its gain without any positive or negative feedback. Ideally, this gain would be infinite, but in practice, real values typically range from approximately 20,000 to 200,000 ohms.
• Input impedance, defined as the ratio of input voltage to input current, is assumed to be infinite in ideal operational amplifiers to prevent any current from flowing from the source to the amplifier.
• In an ideal operational amplifier, the output impedance is assumed to be zero. This impedance is effectively in series with the load, thereby increasing the available output for the load.
• The bandwidth of an ideal operational amplifier is infinite, enabling it to amplify signals across the entire frequency spectrum from DC to the highest AC frequencies. However, the bandwidth is limited by the Gain Bandwidth product, which represents the frequency at which the amplifier’s gain becomes unity.
• In an ideal scenario, the output of an amplifier is zero when there is no voltage difference between the inverting and non-inverting inputs. However, real-world amplifiers exhibit a small output offset voltage.

Operational Amplifier Types

Operation amplifiers can be used in multiple applications. To utilize them in some specific scenario, their circuit is constructed accordingly, giving rise to multiple types. Some of the types of Op Amps are given below, and their applications are also discussed.

Voltage Follower

The voltage follower stands as one of the simplest operational amplifier circuits, devoid of any external components. In this configuration, the output voltage mirrors the input voltage precisely. Consequently, the voltage follower configuration enables the creation of a high-impedance input and a low-impedance output. This is useful to interface logic levels between two components or when a power supply is based on a voltage divider.

Figure 2: Voltage Follower Configuration

Vs=Ve

Applications of Voltage Follower

This is essential for impedance matching and signal buffering, preventing source loading. In power supply circuits, they ensure stable output voltages, which is crucial for maintaining consistent power delivery to sensitive electronic devices despite load variations.

Inverting Op Amp

In this configuration, feedback is established by connecting the output to the negative (inverting) input via a resistor (R2), while the input signal is applied to this inverting pin through another resistor (R1). The positive input pin is grounded. This setup becomes particularly evident when R1 and R2 are equal. Under this circumstance, the configuration enables the generation of a signal that is complementary to the input, as the output mirrors the inverse of the input signal where its values are dependent upon attached resistors (R1 and R2).

Figure 3: Inverting Operational Amplifier

Vs=-Ve (R2/R1)

The negative sign inherent in this setup indicates that the output and input signals are out of phase if there is a need for input and output signals to be in phase, a non-inverting amplifier configuration is employed, discussed in the next section.

Applications of Inverting Op Amp

Widely employed for signal inversion in applications requiring critical phase reversal, such as audio processing and feedback control systems. For instance, audio amplifiers utilize the inverting configuration to achieve phase cancellation, enhancing sound quality for a cleaner output.

Non-inverting Op Amp

This setup closely resembles the inverting operational amplifier configuration. However, in the case of the non-inverting amplifier, the input voltage is directly connected to the non-inverting pin, while the end of the feedback loop is grounded. Both setups allow for the amplification of a single signal. To amplify multiple signals, one can employ summing amplifiers.

Figure 4: Non-Inverting Operational Amplifier

Vs=Ve(1+(R1/R2))

Applications of Non-Inverting Op Amp

Used for buffering signals and impedance matching, ensuring compatibility between input and output impedances. In real-world applications like signal conditioning for sensor interfacing, where preserving the original signal phase is vital, operational amplifiers play a key role.

The Integrator Amplifier

An op amp integrator is a circuit that employs an operational amplifier (op amp) and a capacitor to perform integration, which calculates the area under a curve or function over time. Essentially, it produces an output voltage that mirrors the negative integral of the input voltage, adjusting according to both the duration and amplitude of the input signal.

Figure 5: Integrator Operational Amplifier

Vs = -1/(RC) ∫Ve dt

Op amp integrators serve various purposes, including analog-to-digital converters (ADCs), analog computers, and wave-shaping circuits. For example, they can transform a square wave input into a triangular wave output or convert a sine wave input into a cosine wave output.

Applications of Integrator Amplifier

Frequently employed in wave shaping and analog computing tasks, operational amplifiers play a significant role in mathematically integrating input signals. In practical scenarios such as signal processing within control systems, where integration is essential for tasks like velocity control, operational amplifiers prove invaluable.

Selection of Best Op Amp

Below are essential considerations when selecting the appropriate operational amplifier for your application

Operating Voltage Range: Start by ensuring the op amp can accommodate your expected voltage range. Check the amplifier’s power supply voltages for this information. Typically, supply voltages will be either VDD (+) and ground (single supply) or both positive and negative supplies. A negative supply becomes valuable if negative voltages are necessary for the output.

Gain Bandwidth Product (GBP): Assess the amplifier’s GBP, especially if your application involves higher frequencies or demands superior performance with minimal distortion. Select the op amps with higher Gbps to meet these requirements effectively.

Power Consumption: Consider the power consumption, particularly for applications requiring low power operation. Refer to the part’s datasheet for recommended power requirements, typically listed as supply current and power consumption. You can estimate power consumption by multiplying the supply current by the supply voltage. Generally, op amps with lower supply currents tend to have lower GBPs, correlating with lower circuit performance.

Input Offset Voltage: For applications demanding high accuracy, closely examine the amplifier’s input offset voltage. This voltage introduces an offset in the amplifier’s output voltage and warrants special attention from the designer.

Best Op Amps Available in the Market

Various semiconductor manufacturers have designed a range of Op amps with different features suitable for different applications and environmental conditions. Here, some of the top Op amps are listed.

LM358DR2G Operational Amplifier

The LM358DR2G operational amplifier from Onsemi is a versatile component designed for precise voltage amplification and signal processing. Housed in a plastic/epoxy package with gull wing terminals for surface mounting, it features a maximum input offset voltage of 7000 μV and a minimum voltage gain of 15000. Operating on a supply voltage range of ±1.5/±15/3/30 V, it offers a nominal unity gain bandwidth of 1000 kHz and high common mode rejection ratios. With a maximum operating temperature of 70°C and minimum operating temperature of 0°C, it meets commercial-grade temperature requirements, making it suitable for various electronic applications.

LM358DT Operational Amplifier

The LM358DT operational amplifier by STMicroelectronics, Housed in a plastic/epoxy package with gull wing terminals for surface mounting, offers a maximum input offset voltage of 9000 μV and a minimum voltage gain of 25000. Operating on a supply voltage range of ±1.5/±15/3/30 V, it features a nominal unity gain bandwidth of 1100 kHz and frequency compensation, with a maximum operating temperature of 70°C and minimum operating temperature of 0°C.

OPA2277UA/2K5 Operational Amplifier

The OPA2277UA/2K5 operational amplifier, produced by Texas Instruments, is encased in a plastic/epoxy package with gull wing terminals for surface mounting. This op amp features a maximum input offset voltage of 100 μV and an impressive minimum voltage gain of 1995000. Operating on a supply voltage range of ±2/±18 V, it offers a nominal unity gain bandwidth of 1000kHz and boasts low offset and bias currents. With a wide temperature range from -40°C to 85°C and a compact package size, it is suitable for various industrial applications where precision and reliability are paramount. Additionally, with features like high common mode rejection ratios and low power consumption, the OPA2277UA/2K5 op amp offers excellent performance in demanding environments.

LM358ADR Operational Amplifier

The LM358ADR operational amplifier from Texas Instruments is a versatile component suitable for various electronic applications. Encased in a plastic/epoxy package with gull wing terminals for surface mounting, it features a maximum input offset voltage of 5000 μV and a minimum voltage gain of 25000. Operating on a supply voltage range of ±1.5/±15/3/30 V, it offers a nominal unity gain bandwidth of 700 kHz and frequency compensation, with a wide temperature range from 0°C to 70°C and compact package size. Additionally, with features like high common mode rejection ratios, it ensures stable performance in demanding environments.

Conclusion

Conclusively, operational amplifiers (Op Amps) play a crucial role in modern electronics, offering versatile solutions across a wide range of applications. Whether it’s a basic voltage follower or a complex integrator, Op Amps provide engineers with the flexibility to design circuits tailored to specific needs in consumer electronics, industrial automation, and scientific instrumentation. Selecting the best Op Amp involves careful consideration of factors like operating voltage range, gain-bandwidth product, power consumption, and input offset voltage to ensure optimal performance. By mastering the fundamentals of Op Amp operation and understanding different circuit configurations, designers can effectively leverage these essential components in electronic design.

Fatima Razzaq

Fatima Razzaq is a freelance technical writer who served as an electrical engineering lecturer at Air University—a federally chartered public sector research university in Pakistan. Razzaq holds a Bachelor’s degree with distinction in electronic engineering from Ghulam Ishaq Khan Institute of Engineering Sciences and Technology (GIKI) and a Master’s degree in Sustainable Transportation and Electrical Power Systems from the University of Nottingham, Universidad de Oviedo, and La Sapienza University of Rome. Razzaq’s diverse work experiences in academia and industry continue to inform her prolific technical writing journey in the areas of electrical engineering, storage mechanisms, power electronics, electric vehicles, energy, and related topics.

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