The basics of operational amplifiers in analog circuit fundamentals are well known to electronics engineers. This article will introduce the basics of the principles, symbols, and circuit models of inherited circuit op amps.
Integrated circuit operational amplifierThe integrated circuit operational amplifier is a high-gain multi-stage direct-coupled voltage amplifier. It uses an integrated process to fabricate a large number of semiconductor transistors, resistors, capacitors and other components and their wiring on a single crystal silicon chip.
It was originally used for signal calculations, so it is called an integrated operational amplifier, or simply an integrated operational amplifier. The basic structure usually consists of four parts, namely the input stage, the intermediate stage, the output stage, and the bias circuit.
National standard symbols and common symbols
The circuit model of the integrated op amp:
Input resistance rid, output resistance ro, controlled voltage source Aoduid, uid=u+−u−, Aod is open-loop voltage amplification
The relationship between uo and uid is similar to the relationship of the maximum undistorted output voltage Uomax, which is divided into linear region and nonlinear region.
Ideal op amp, ideal for performance of machine-integrated op amps
Open loop voltage gain Aod=∞
Input resistance rid=∞
Output resistance ro=0
Conversion rate SR=∞
The output of the amplifying circuit is in some way back to the input to affect the input amount, which is called feedback.
If the result of the feedback reduces the output change, it is called negative feedback, and vice versa.
Linear zone characteristics1. Input voltage uid is equal to zero
Uo=Aoduid=Aod(u+−u−)
Since uo is a finite value and Aod=∞, the input voltage uid=0(u+−u−)
Input - called virtual short.
2. The input current is equal to zero
Since the ideal op amp input resistance is infinite, the current flowing into the two inputs of the ideal op amp is:
I−=i+=uidrid≈0
Input - called virtual break.
Nonlinear zone characteristics1. The input voltage is only high and low
Uo={ UOHUOLu+》u−u+“u−
2. The input current is equal to zero
Has "virtual break", but generally does not have the characteristics of "virtual short"
The integrated op amp must introduce deep negative feedback to ensure that it works in the linear region. The application circuit working in the linear region mainly includes the arithmetic circuit and the active filter circuit.
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