Operational Amplifier(OP Amp) Tutorial



Principle

When an operational amplifier is used, its output is connected to its inverTIng input node to form a negative feedback configuration—negaTIve. The reason is that the voltage gain of the operational amplifier is very large, ranging from hundreds to tens of thousands of times, the use of negative feedback to ensure the stable operation of the circuit. But that doesn't mean the operational amplifiers can't be connected to the positive feedback. On the contrary, in many systems that need to generate oscillatory signals, OP Amp with positive feedback configuration is a common component.

The Schematic Diagram of Basic Operational Amplifier

The Schematic Diagram of Basic Operational Amolifier

Abbreviation: OP Amp

In an actual circuit, the feedback network is usually combined to form a certain functional module. Since it was used in analogue computer to realize mathematical operation, it is named "operational amplifier", which continues to this day. Operational amplifier is a circuit unit based on its function, which can be implemented by discrete devices or semiconductor chips. With the development of semiconductor technology, the vast majority of operational amplifiers are in the form of single chip. Nowadays, there are many kinds of operational amplifiers, which are widely used in almost all industries.

History

Summing AmplifierIn 1941, the first operational amplifier composed of vacuum tubes was invented by Karl D. Swartzel Jr. Of Bell Labs and got the American patent 2,401,779, named “Summing Amplifier”.
model K2-WIn 1952, model K2-W, the first operational amplifier with vacuum tube was sold by George A. Philbrick Researches (GAP/R) in the market.
μA702In 1963, the first operational amplifier in the form of a single IC chip was the μA702 designed by Fairchild Senmiconductors's Bob Widlar, and it was introduced after modification in 1965 named μA709. 
μA741In 1968, Fairchild Semiconductor Inc. Introduced the μA741 still in production, it is one of the most successful operational amplifiers of all the time and one of the very few oldest IC models.


In 1941, the first operational amplifier composed of vacuum tubes was invented by Karl D. Swartzel Jr. Of Bell Labs and got the American patent 2,401,779, named “Summing Amplifier”.

In 1952, model K2-W, the first operational amplifier with vacuum tube was sold by George A. Philbrick Researches (GAP/R) in the market.

In 1963, the first operational amplifier in the form of a single IC chip was the μA702 designed by Fairchild Senmiconductors's Bob Widlar, and it was introduced after modification in 1965 named μA709. 

In 1968, Fairchild Semiconductor Inc. Introduced the μA741 still in production, it is one of the most successful operational amplifiers of all the time and one of the very few oldest IC models.

Types

General type: Its performance parameters are suitable for general use (low frequency and slow signal change), such as 741A, LM358 (double OP Amp), LM324 and LF356  with FET as input stage.

High-Z type: The characteristic of this kind of amplifier is that the input impedance of differential mode is very high and the input bias current is very small. The main measure to achieve these targets is to make use of the high input impedance of FET, but the input offset voltage of this kind of operational amplifier is larger. Such operational amplifier have LF356, LF355, LF347, CA3130, CA3140, etc.

Low-temperature drift type: In precision instruments, weak signal detection and other automatic control instruments, the bias voltage of operational amplifier is small and does not change with the temperature. The low temperature drift operation amplifier is designed for this purpose. At present, the commonly used operational amplifier has OP07, OP27, OP37, AD508 and ICL7650 composed of MOSFET device and so on.

High slew-rate type: In fast A/D converter, D/A inverter and video amplifiers, the conversion rate of the operational amplifier must be high, and the BWG of the unit gain bandwidth must be large enough. Common operational amplifier has LM318, 175A and so on.

Low -consumption type: Due to the wide application of portable instruments, low power supply and low power consumption must be used. Commonly used low-power operational amplifier has TL-022C,TL-160C and so on.

High voltage and power type: The output voltage of operational amplifier is mainly limited by power supply. In ordinary operational amplifier, the maximum output voltage is only dozens of volts and the output current is only dozens of Ma. In order to increase the output voltage and current, the auxiliary circuit must be added to the external circuit of the operational amplifier. High-voltage and high-power operational amplifier can output high voltage and high current without any additional circuit.

Features

Main features

The input resistance is very high, the output resistance is very small, the voltage magnification is very large, and the zero drift is very small.

Characteristics of ideal operational Amplifier in Linear region

Virtual Ground: When the operational amplifier is in a linear state, the potential of the inverse input is zero.

Virtual Short Circuit: When the operational amplifier is in a linear state, the two input terminals can be regarded as equipotential, which is called virtual short circuit. But both sides are not real short circuit.

Virtual Open Circuit: When the operational amplifier is in a linear state, two input terminals can be regarded as equivalent open circuit, which is called virtual open circuit. Obviously, it doesn’t break the two inputs actually.

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