1. Introduction

As a key component in analog integrated circuits, operational amplifiers have played a crucial role in the field of automatic circuit design in the past decades. Operational amplifiers (op-amps) are used almost everywhere from simple linear amplifiers to complex signal processing systems. In 1928, Harold S.Black applied for a patent on his feedback amplifier invention. In 1947, operational amplifiers were first referred to by name in Ragazzini’s key paper [1]. Despite such a long time, many of the basic performance characteristics of op-amp are poorly understood. This research will help people to learn about op-amp.

Firstly, the basic principles and circuit models of op-amps are the basis for understanding their operating characteristics. Through experiments and simulations, researchers have deeply analyzed these non-ideal factors and proposed corresponding compensation and optimization strategies. Secondly, op-amp is widely used in analog circuit design. The application of op-amp in basic amplifier circuits, filter design, and signal processing circuits is detailed in the literature [2]. The application of Amp in automatic control circuit design is also indispensable. In the design of a feedback control systems, op-amps can realize proportional (P), integral (I), and differential (D) control to form a PID controller, which is used to improve the stability and dynamic performance of the system [3]. The application of op-amp in PID controllers has been thoroughly studied in the literature, including parameter tuning, performance optimization, and stability analysis [4].

With the development of technology, the innovative applications of op-amp in modern circuit design are also emerging. In the power management circuit, the op-amp is used for voltage regulation, current sensing, and battery management to ensure stable power supply of the system. In the low-power design strategy, a low-power version of op-amp [5] was developed to meet the requirements of portable and wireless devices.

In summary, op-amps are extremely widely used in automatic circuit design and are indispensable components for everything from basic analog circuits to complex digital and control systems. This research explores basic applications of op-amps and innovative designs that improve its performance, enhancing the automation and efficiency of circuit design.

2. OP-AMP Basic Principle

2.1. OP-AMP Circuit Model

The circuit model of an operational amplifier is the basis of understanding and analyzing operational amplifier's working principle. In the ideal case, an operational amplifier has infinite input impedance, zero output impedance, infinite gain and bandwidth, and a perfect linear response. However, in practice, the performance of operational amplifiers is limited by several factors, including limited gain, bandwidth, input and output impedance, and nonlinear effects.

The basic circuit model of an operational amplifier usually includes the following four key parts.

The differential input stage is responsible for amplifying the difference between the input signal, that is, the potential difference between the two input terminals (the in-phase end and the anti-phase end). The differential input stage provides the high common Mode rejection ratio (CMRR) of the op-amp, which can effectively suppress the common mode noise.

After the differential input stage, the signal will be further amplified in the high-gain amplifier stage. This stage is usually designed to have a very high voltage gain to provide sufficient open-loop gain.

The output stage is responsible for driving the signal output of the high-gain amplifier stage to the external circuit. The output stage needs to be able to provide sufficient current to meet the load demand while maintaining a low output impedance.

The performance of an op-amp depends heavily on the design of its feedback network. Negative feedback stabilizes gain, extends bandwidth, reduces distortion, and improves input impedance.

2.2. Characteristics of Indel Operational Amplifier

An ideal operational amplifier (Op Amp) is a linear amplifier with theoretically infinite gain and bandwidth. In practice, the characteristics of the ideal operational amplifier provide great convenience for the circuit design, so that the designer can ignore many complex nonlinear factors and focus on the functional realization of the circuit. Here are some key features of an ideal operational amplifier.

An ideal op amp has infinite gain for differential input signals. In practice, real devices will have quite a high gain, but this gain won’t necessarily be precisely known. The input impedance of an ideal operational amplifier is infinite, which means that it does not draw any current from the signal source. This property allows the operational amplifier to be connected to a high-impedance signal source without causing load effects on the signal source.

The output impedance of an ideal operational amplifier is zero, which means that it can supply the required current to any load without affecting the output voltage.

The frequency response of an ideal operational amplifier is infinitely wide, which means that it can amplify all signals from DC to infinitely high frequencies without any distortion.

The ideal operational amplifier input offset voltage is zero, which means that when the two input voltages are equal, the output voltage will also be zero.

The ideal op-amp can completely suppress the common mode signal, that is, when the same signal is received at the two inputs at the same time, the signal will not appear at the output.

The gain of an ideal operational amplifier for a differential mode signal (that is, the voltage difference between the two inputs) is infinite, which ensures that the differential signal is accurately amplified even in the presence of common-mode noise.

These properties of ideal operational amplifiers make them very useful in analog circuit design, especially in applications where high accuracy and linear response are required. However, practical operational amplifiers will be physically limited and cannot fully achieve these ideal characteristics, so designers need to consider these non-ideal factors in practical applications.

2.3. Non-ideal Factor Analysis

In practice, the performance of operational amplifiers (op-amps) is often affected by non-ideal factors, which may cause the actual performance of the circuit to deviate from the ideal situation. Non-ideal factor analysis is crucial to understanding and optimizing the performance of op-amps. There are two types of error sources in op-amps, and they fall under the general classification of DC and AC errors.

Some non-idealities cause DC errors [6]. Firstly, the input of an operational amplifier is not infinitely high in impedance as ideal. In fact, there is a small input bias current. These currents flow into or out of the input, which may cause the input voltage to shift and affect the accuracy of the circuit. When designing high-precision circuits, the influence of the input bias current must be considered, and corresponding measures should be taken to reduce its influence on the circuit performance. Secondly, the input offset voltage is the voltage difference between the two inputs of an op-amp in the absence of an input signal. This voltage difference should be zero even under ideal conditions, but in practice input offset voltages may exist due to mismatches in the manufacturing process, which causes the output of the amplifier to appear DC offset in the absence of input signals.AC errors are flighty, so they are addressed here by developing a set of nonideal equations that account for AC errors. The ac errors may show up under DC conditions, but they get worse as the operating frequency increases. A good example of an AC error is the common-mode rejection ratio (CMRR). Most op-amps have a guaranteed CMRR specification, but this specification is only valid at DC or very low frequencies [6].

The performance of operational amplifiers can be affected by the environment. For example, the input bias current and input offset voltage may vary with temperature, which can lead to unstable performance of the circuit. The temperature has effects on the needed power to disturb the op-amp circuit. Even if the variation due to temperature seems small, in a harsh environment context (higher temperature) or by considering a complex electronic systems, stronger variations in the immunity characteristics can be expected [7]. Therefore, when designing the circuit, it is necessary to consider the effect of temperature drift and take appropriate temperature compensation measures.

Through the analysis of these non-ideal factors, engineers can better understand the actual performance of op-amps and take corresponding measures to optimize the performance and improve the stability and accuracy of the circuit when designing the circuit.

3. Application of OP AMP in Automatic Control Circutt Design

3.1. Basic Amplifier Circuit Design

In the design of a basic amplifier circuit, operational amplifier (op-amp) plays a crucial role. It can amplify weak electrical signals and improve the sensitivity of the system. A typical basic amplifier circuit consists of an operational amplifier and several peripheral components such as resistors and capacitors. The configuration of these components determines the gain, input impedance, and output impedance of the amplifier circuit.

The first is a simple inverting amplifier design. An amplifier generally accepts a small signal at its input and produces a larger, amplified version of the signal at its output [8]. In this circuit, the inverting input of the op-amp is connected to the input signal through a resistor, which is also grounded through another resistor. The output then feeds back directly to the inverting input. By choosing an appropriate resistance value, the desired voltage gain can be set. The advantage of this configuration is that the input impedance is lower, and it is suitable for low-impedance signal sources.

The op-amp is also used in in-phase amplifier design. In this circuit, the input signal is directly connected to the in-phase input of the operational amplifier, and the feedback network is connected from the output to the in-phase input through a resistor, which is also grounded through another resistor. The in-phase amplifier is characterized by high input impedance, which is suitable for high-impedance signal sources and does not produce phase reversal.

In addition to the inverting and in-phase amplifiers, there are differential amplifier designs. A differential amplifier is able to amplify the difference between two input signals while suppressing the common-mode signal. Such circuits are very useful in applications that require a high common mode rejection ratio, for example in sensor signal processing.

The frequency response, noise performance and distortion characteristics of the op-amp should also be considered when designing the basic amplifier circuit. With appropriate circuit design and component selection, these parameters can be optimized to meet the needs of specific applications.

3.2. Feedback Control System Design

Feedback control is a widely used control strategy in automatic control systems by measuring the output of the system and comparing it with a desired reference input to generate an error signal. This error signal is subsequently used to adjust the input of the system in order to reduce the error and bring the output of the system closer to the desired value. Operational amplifiers are very suitable for implementing feedback control systems because of their high gain, high input impedance and low output impedance.

3.2.1. Basic principle of feedback control and the role of operational amplifier in feedback control

Feedback control systems usually consist of several basic components: a controlled plant, sensor, controller, and actuator. The controlled object is the system or process to be controlled, the sensor is used to measure the output of the system, the controller generates the control signal based on the feedback signal, and the actuator adjusts the input of the controlled object based on the control signal.

Operational amplifiers are commonly used as part of the controller in feedback control systems. It can amplify the error signal and stabilize the output of the system by negative feedback. Negative feedback reduces the gain by feeding a part of the output signal back to the input of the operational amplifier, but at the same time, it also improves the stability of the system.

3.2.2. Design and implementation of feedback control system

When designing a feedback control system, the dynamic characteristics, stability and performance indexes of the system should be considered. The selection and configuration of operational amplifiers are crucial to meet these requirements. For example, the gain of the system can be set by adjusting the resistance value of the feedback network, and the stability can be improved by introducing the compensation network to improve the phase margin and amplitude margin of the system.

It is also necessary to consider non-ideal factors in practical circuits, such as the bandwidth limitation of operational amplifiers, noise and distortion, and parasitic components in the circuit, when implementing feedback control systems. Each of these factors may affect the performance of the system and therefore needs to be properly considered and optimized at design time.

3.3. PID Controller a Sample of Feedback Control System Design

In the PID controller, the op-Amp plays a crucial role. PID controller is a common feedback control algorithm, which corrects the deviation of the system through the combination of proportional (P), integral (I) and differential (D) control methods to achieve the purpose of stable and accurate control. Because of its characteristics of high gain, high input impedance and low output impedance, the operational amplifier is very suitable for the analog circuit design of PID controller.

Firstly, the operational amplifier can be used to implement the proportional link in the PID controller. By configuring an appropriate feedback network, the op-amp can provide the desired gain to amplify the bias signal of the system. This configuration usually involves a simple resistive divider network that is used to set the value of the proportional gain.

Secondly, the application of operational amplifiers in the integration link is equally important. The integration link is used to eliminate the steady-state error of the system, and by integrating the deviation signal, an output proportional to the integral value of the deviation signal can be generated. The op-amp integrator is also called a precision integrator because of its high degree of accuracy [9].

Finally, the application of operational amplifiers in the differentiation link cannot be ignored [9]. The circuit yields an output that is proportional to the time derivative of the input. The proportionality constant is set by R and C. The differential link can predict the future behavior of the system and help to improve the dynamic response of the system. By adding a capacitor to the input of the operational amplifier, the differentiation of the bias signal can be achieved to obtain an output proportional to the rate of change of the bias signal.

In a word, the application of op-amp in PID controllers is various. It can not only realize proportional, integral and differential control modes, but also ensure the stability and accuracy of the control system through its high-performance characteristics. In practice, the performance of the PID controller can be effectively improved to meet various control requirements by properly designing the circuit configuration of op-amp.

4. Innovative Application of OP AMP in Modern Circutt Design

4.1. Power Management Circutt

In modern electronic systems, power management circuits play a crucial role as they are responsible for converting external power sources into stable voltages and currents required by the internal components of the system. As a kind of high-performance analog circuit component, op-amps are widely used in power management circuits [10].

Firstly, operational amplifiers can be used to build efficient voltage regulators. By configuring an appropriate feedback network, the op-amp can achieve precise control of the output voltage, thus ensuring the stability of the power supply output. For example, in switching mode power supplies (SMPS), operational amplifiers can be used to compare the reference voltage with the feedback voltage in order to adjust the switching frequency or duty cycle to achieve output voltage regulation.

Secondly, operational amplifiers also play an indispensable role in current sensing and protection circuits. By configuring the operational amplifier as a differential amplifier, the current flowing through the load can be accurately detected and converted into a voltage signal. This signal can be used for overcurrent protection, that is, when the detected current exceeds a set threshold, the op-amp can trigger the protection circuit to cut off the power or limit the current to protect the system from damage.

Finally, the op-amp can also be used for dynamic response optimization of the power supply. When the load changes, the power supply needs to quickly adjust the output to maintain voltage stability. The high gain and wide bandwidth characteristics of operational amplifiers enable them to respond quickly to load changes, and by adjusting the feedback network, the transient response of the power supply can be optimized to improve the performance of the overall system.

In summary, the application of operational amplifiers in power management circuits not only improves the stability and efficiency of the power supply, but also enhances the reliability and security of the system. With the development of electronic technology, the design and application of operational amplifiers will continue to play an important role in the field of power management.

4.2. Low-power Design Strategy

Low-power strategies have become key considerations in modern circuit design, especially in portable and battery-powered devices. The op-amp is the core component of analog circuit design, and its application in low-power design is particularly important. This section explores how to implement low-power circuit designs using op-amps and discusses some effective strategies and techniques.

The first principle of low-power design is to understand and optimize the power sources in the circuit. In operational amplifier circuits, static and dynamic power consumption are the main sources of power consumption. Static power consumption is mainly caused by the bias current and leakage current, while dynamic power consumption is related to the signal switching frequency and load capacitance. An op-amp with low static power consumption should be selected in the design, and the power consumption should be reduced by reducing the operating voltage and current.

In low-power design, it is very important to choose the right operational amplifier. An operational amplifier with a low quiescent current and low input bias current should be selected. In addition, proper configuration of op-amps can also reduce power consumption. For example, using a unity gain configuration reduces the output current and thus the power consumption.

Power management is an important means to achieve low-power design. In the operational amplifier circuit, power on and off can be controlled by a power switch or power management IC to reduce standby power consumption. In addition, dynamically adjusting the operational state of the op-amp, such as switching to low-power mode when high performance is not required, is also an effective way to reduce dynamic power consumption.

Through the above strategies and techniques, the operational amplifier can be effectively used to achieve low-power circuit design and meet the energy efficiency requirements of modern electronic devices.

5. Conclusion

This paper has reviewed the applications of operational amplifiers (op-amps) in automatic circuit design, highlighting their versatility and importance in both analog and digital circuits. The analysis began with the fundamental principles and characteristics of op-amps, moving on to their roles in basic amplification, filtering, and signal processing. The paper also underscored the significance of op-amps in feedback control systems and PID controllers, emphasizing their impact on system stability and performance. Furthermore, it explored innovative applications in power management and low-power design, showcasing the adaptability of op-amps to modern electronic demands. This paper shows that operational amplifiers can be widely and flexibly used in automation circuits, providing engineers with operational amplifier application ideas.

This paper is still flawed in terms of content. This paper fails to enumerate all the functions and innovative applications of operational amplifiers and fails to give specific circuit applications when introducing functions. These can be made up by updating the literature review to include the latest research results.

Future research can focus on improving the energy efficiency ratio of op-amps, developing op-amps adapted to extreme environmental conditions, and exploring the application of op-amps in emerging fields such as wearable devices. In addition, with the advancement of IC technology, it is also interesting to investigate how to further integrate op-amps for more complex circuit functions and how to improve the performance and stability of op-amps through algorithmic optimization.