What is an integrated operational amplifier?

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What is an integrated operational amplifier? [Copy link]

Integrated operational amplifiers are highly versatile active devices. They can be used not only for signal calculation, processing, transformation and measurement, but also for generating sinusoidal or non-sinusoidal signals. They are widely used not only in analog circuits, but also in pulse digital circuits. Therefore, their application circuits are diverse. In order to analyze the principles of these circuits, it is necessary to understand the basic characteristics of operational amplifiers. 1. Open-loop differential-mode voltage transfer characteristics of integrated operational amplifiers When the integrated operational amplifier is in the open-loop state, the relationship between the output voltage UO and the differential-mode input voltage Uid = U- - U+ is called the open-loop differential-mode transfer characteristic. The open-loop differential-mode transfer characteristic curve obtained by theoretical analysis and experiment is shown in Figure Z0609. The curve shows that the op amp has two working areas: the linear area (shaded part) and the nonlinear area (area on both sides of the shaded area). In the linear area: UO = Aod (U- - U+), that is, the output voltage is linearly related to the input voltage. Since Uomax is limited and the open-loop voltage gain Aod of the general op amp is very large, the linear area is very small. When applied, a deep negative feedback network should be introduced to ensure that the op amp works stably in the linear area. In the nonlinear area, UO has nothing to do with Uid, and it has only two possible values, namely the positive saturation voltage +Usat (U+ ＞U- ) and the negative saturation voltage -Usat (U-＞U+). The properties of the op amp are completely different in the two regions. Therefore, when using and analyzing the application circuit, we must first determine the working region of the op amp. 2. Two important characteristics of the ideal op amp In order to highlight the main characteristics and simplify the analysis process, when analyzing the actual circuit, the actual op amp is generally treated as an ideal op amp. The so-called ideal op amp refers to an op amp with the following ideal parameters: Open-loop voltage gain Aod = ∞ Input resistance rid = ∞ Output resistance ro = 0 Bandwidth B = ∞ Common-mode rejection ratio CMRR = ∞ Input bias current IB1 = IB2 = 0 Offset and temperature drift are both zero. The ideal op amp does not exist, however, with the development of integrated circuit technology, the parameters of modern integrated op amps are very close to those of ideal op amps. Practice shows that using an ideal op amp as a simplified model of an actual op amp, the results of analyzing the op amp application circuit are basically consistent with the experimental results, and the error is within the engineering allowable range. Therefore, when analyzing actual circuits, except for circuits that require analysis errors, actual op amps can be treated as ideal op amps to reasonably simplify the analysis process. An ideal op amp working in the linear region has two important characteristics: 1. The potentials of the two input terminals of the ideal op amp are equal. Because U--U+=UO/Aod, and Aod =∞, UO is a finite value, so: U- = U+ GS06004 2. The input current of an ideal op amp is zero, because rid = ∞, so: Ii＝0 GS06005 These two characteristics greatly simplify the analysis process of op amp application circuits and are the basic basis for analyzing various circuits in which op amps work in the linear region. These two characteristics are often summarized by the concept of "virtual short". The so-called "virtual short" means that the two input terminals are short-circuited for voltage, but open-circuited for current. When operating, the op amp has a certain positive feedback or negative feedback network. Therefore, when analyzing, we must first determine the working state of the op amp. The basis for determining the working state is: (1) If U->U+, the op amp works in the linear region; (2) If U+≥U-, the op amp works in the nonlinear region. When an ideal op amp works in the nonlinear region, it also has two basic characteristics: (1) The input current of the op amp is zero, that is, Ii=0; (2) The output voltage has two possible values: U-＞U+ then UO = - Usat U+ ＞U- then UO = Usat U+ = U- is just the transition point between two states. To summarize, when analyzing an op amp application circuit, first treat the actual op amp as an ideal op amp, then determine the op amp's working state, and finally, perform analysis and calculation based on the characteristics of each region combined with circuit analysis theory.