EECE310_Chapter_9_Lecture_Notes__F05_

# EECE310_Chapter_9_Lecture_Notes__F05_ - College of...

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Unformatted text preview: College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers In this chapter, the discussion shifts to an important electronic device called an operational amplifier (op amp). Operational amplifiers are integrated circuits (ICs) that are employed in a wide-variety of engineering instrumentation. Op amps originated in analog circuits to perform mathematical operations, such as the integration and addition of signals. EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers The ideal op amp is a differential amplifier which has both inverting and non-inverting terminals (Chapter 8). The input signal of the differential amplifier consists of a differential component and a commonmode component. EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers The difference between the input voltages of the op amp is called the differential signal: v idiff = v1 - v 2 The average of the op amp's input voltage is known as the common-mode signal: v icm EECE 310 Preston D. Frazier, Ph.D., P.E., PMP ( v1 + v 2 ) = 2 College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers Characteristics of an ideal op amp: Infinite input impedances (Zi) Infinite gain for the differential input signal (Av) Zero-gain for a common-mode input signal Zero output impedance (Z0) Infinite bandwidth EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers Important Note about Ideal Operational Amplifiers: If the op amp has external feedback, the output voltage of the op amp will do whatever is necessary to make the differential signal equal to zero and the inputs draws no current. EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers Operational amplifiers are almost always used with negative feedback, in which part of the output signal is returned to the input in opposition of the source signal. In conclusion, we'll discuss the two most popular op amps, which have two resistors connected to the op amps to create an amplifier circuit with a gain which depends only on the ratio of the two resistors. EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers Inverting Amplifier EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers The closed-loop voltage gain of an inverter is determined solely by the ratio of the impedances. AV = - Rf R1 The output voltage is equal to the negative ratio of the impedances multiplied by the input voltage: EECE 310 Preston D. Frazier, Ph.D., P.E., PMP v0 = - Rf R1 v in College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers Non-Inverting Amplifier EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 9 Operational Amplifiers The closed-loop voltage gain of a non-inverter is ascertained from the ratio of the impedances. A = 1+ V Rf R1 f The output voltage is equal to sum of the impedances multiplied by the input voltage and divided by the input resistance: R +R EECE 310 Preston D. Frazier, Ph.D., P.E., PMP v0 = 1 R1 v in ...
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## This note was uploaded on 10/15/2008 for the course EECE 310 taught by Professor Frazier during the Fall '08 term at Howard.

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