TAILIEUCHUNG - OPERATIONAL AMPLIFIERS

The operational amplifier (Op Amp) is one of the versatile electronic circuits. It can be used to perform the basic mathematical operations: addition, subtraction, multiplication, and division. | Attia John Okyere. Operational Amplifiers. Electronics and Circuit Analysis using MATLAB. Ed. John Okyere Attia Boca Raton CRC Press LLC 1999 1999 by CRC PRESS LLC CHAPTER ELEVEN OPERATIONAL AMPLIFIERS The operational amplifier Op Amp is one of the versatile electronic circuits. It can be used to perform the basic mathematical operations addition subtraction multiplication and division. They can also be used to do integration and differentiation. There are several electronic circuits that use an op amp as an integral element. Some of these circuits are amplifiers filters oscillators and flip-flops. In this chapter the basic properties of op amps will be discussed. The non-ideal characteristics of the op amp will be illustrated whenever possible with example problems solved using MATLAB. PROPERTIES OF THE OP AMP The op amp from a signal point of view is a three-terminal device two inputs and one output. Its symbol is shown in Figure . The inverting input is designated by the - sign and non-inverting input by the sign. Figure Op Amp Circuit Symbol An ideal op amp has an equivalent circuit shown in Figure . It is a difference amplifier with output equal to the amplified difference of the two inputs. An ideal op amp has the following properties infinite input resistance zero output resistance zero offset voltage infinite frequency response and infinite common-mode rejection ratio infinite open-loop gain A. 1999 CRC Press LLC Figure Equivalent Circuit of an Ideal Op Amp A practical op amp will have large but finite open-loop gain in the range from 105 to 109. It also has a very large input resistance 106 to 1010 ohms. The output resistance might be in the range of 50 to 125 ohms. The offset voltage is small but finite and the frequency response will deviate considerably from the infinite frequency response. The common-mode rejection ratio is not infinite but finite. Table shows the properties of the general purpose 741 op amp. Table .

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