An operational amplifier is a circuit unit with a very high amplification factor. In the actual circuit, it is usually combined with the feedback network to form a certain functional module. It is an amplifier with special coupling circuit and feedback. The output signal can be the input signal +, - or the result of digital operations such as differentiation and integration.
Because it was used in analog computers in the early days to realize mathematical operations, it was named "operational amplifier". An op amp is a circuit unit named from a functional point of view, which can be implemented by discrete devices or in semiconductor chips. With the development of semiconductor technology, most op amps exist in the form of a single chip. There are many types of op amps, which are widely used in the electronics industry.
working principle
The op amp as shown in the figure has two input terminals a (inverting input terminal), b (non-inverting input terminal) and an output terminal o. Also known as Inverting Input Non-Inverting
input and output. When the voltage U- is added between the a terminal and the common terminal (the common terminal is the point where the voltage is zero, it is equivalent to the reference node in the circuit.), and its actual direction is higher than the common terminal from the a terminal, the output voltage The actual direction of U is from the common end to the o end, that is, the directions of the two are exactly opposite. When the input voltage U+ is added between the b terminal and the common terminal, the actual directions of U and U+ are exactly the same relative to the common terminal. For the sake of distinction, terminals a and b are marked with "-" and "+" respectively, but do not mistake them for the positive and negative polarities of the voltage reference direction. The positive and negative polarities of the voltage shall be marked separately or indicated by arrows. Inverting and non-inverting amplifiers are shown below:
Generally, an operational amplifier can be simply regarded as a high-gain direct-coupled voltage amplifying unit with a signal output port (Out) and two high-impedance input terminals of non-inverting and inverting. . [2]
The power supply mode of the op amp is divided into dual power supply and single power supply. For a dual-supply op amp, its output can vary on both sides of zero voltage, and the output can also be set to zero when the differential input voltage is zero. Using a single-supply op amp, the output varies within a certain range between the supply and ground.
The input potential of the op amp is usually required to be higher than a certain value of the negative power supply and lower than a certain value of the positive power supply. A specially designed op amp can allow the input potential to vary from the negative supply to the positive supply, even slightly above the positive supply or slightly below the negative supply. Such op amps are called rail-to-rail input op amps.
The output signal of the operational amplifier is proportional to the signal voltage difference between the two input terminals. In the audio segment, there are: output voltage = A0 (E1-E2), where A0 is the low-frequency open-loop gain of the operational amplifier (such as 100dB, or 100,000 times) , E1 is the input signal voltage of the non-inverting terminal, and E2 is the input signal voltage of the inverting terminal.
Classification of amplifiers
General Purpose Integrated Operational Amplifier
The technical parameters of the amplifier are relatively moderate, which can meet the requirements of use in most cases. The general-purpose integrated operational amplifier is divided into type I, type II and type III, among which type I is a low-gain operational amplifier, type II is a medium-gain operational amplifier, and type III is a high-gain operational amplifier. Type I and Type II are basically early products, their input offset voltage is about 2mV, and the open-loop gain is generally greater than 80dB.
High Input Impedance Integrated Operational Amplifier
High Input Impedance Integrated op amps have a very large input impedance and very little input current. The input stage of such operational amplifiers often uses MOS transistors.
High Precision Integrated Operational Amplifier
High-precision integrated operational amplifiers refer to those operational amplifiers with small offset voltage, very small temperature drift, and very high gain and common mode rejection ratio. These op amps are also less noisy. Among them, the offset voltage of the monolithic high-precision integrated operational amplifier can be as small as a few microvolts, and the temperature drift is as small as tens of microvolts per degree Celsius.
High-speed integrated operational amplifier
The output voltage conversion rate of high-speed integrated operational amplifiers is very large, and some can reach 2~3kV/μS
Low Power Integrated Operational Amplifier
The low-power integrated operational amplifier operates with very small current and low power supply voltage, and the power consumption of the entire operational amplifier is only tens of microwatts. Such integrated operational amplifiers are mostly used in portable electronics.
Broadband Integrated Operational Amplifier
The broadband integrated operational amplifier has a wide frequency band, and its unity gain bandwidth can reach more than gigahertz, and is often used in broadband amplifier circuits.
High Voltage Integrated Operational Amplifier
Generally, the power supply voltage of the integrated operational amplifier is below 15V, while the power supply voltage of the high-voltage integrated operational amplifier can reach several tens of volts.
Power Type Integrated Operational Amplifier
The output stage of the power type integrated operational amplifier can provide a relatively large power output to the load.
optical fiber amplifier
Optical fiber amplifiers can not only directly amplify optical signals, but also have real-time, high-gain, broadband, online, low-noise, low-loss all-optical amplification functions, and are essential key components in the new generation of optical fiber communication systems; This technology not only solves the limitations of attenuation on the transmission rate and distance of optical networks, but more importantly, it creates wavelength division multiplexing in the 1550nm frequency band, which will enable ultra-high-speed, ultra-large capacity, ultra-long-distance wavelength division multiplexing (WDM). ), dense wavelength division multiplexing (DWDM), all-optical transmission, optical soliton transmission, etc. have become a reality, which is an epoch-making milestone in the development history of optical fiber communication.
