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Lab_1_DA828447

# Lab_1_DA828447 - ELEC 321 Laboratory Report of Applied...

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1 ELEC 321 Laboratory Report of Applied Electronics III E XPERIMENT #1 FEEDBACK PRINCIPLE & STABILITY ANALYSIS IN MULTIPLE-POLE AMPLIFIER Lo Wang Fu, DA828447 Faculty of Science and Technology, University of Macau Major: EEE Section No. : Section A Lab Date: 14/09/2010, Hand-in Date: 06/10/2010, Instructor: Prof. Tam, Pedro Cheong Abstract — By using negative feedback network, it could stabilize the system, and create a oscillating sinusoidal wave. Keywords Stability, s-plane, voltage mixing voltage sampling, feedback, close-loop gain I. OBJECTIVE It’s to study the basic negative feedback principle and stability analysis with multi-stage amplifiers. II. APPARATUS Components Four Op-Amp chips (UA741), three 0.1uF capacitors, one 1nF capacitor, two 100 Ω resistors, one 1k Ω resistor, five 10k Ω resistors, two 100k Ω resistors, one potentiometer, several pieces of connecting wires. Instrumentation Digital multi-meter, function generator, oscilloscope, prototype board, DC power supply. III. PROCEDURE WITH DATA ANALYSIS A. Set-up and Analyze circuit The building block, consisted of four operational amplifiers connected in cascade and several components, should be constructed on the prototype board firstly, the op-amps could be power up by DC supply with +15V and -15V on the prototype board. Set R a as 10k Ω and R b as 1k Ω . By Thévenin's theorem and Norton’s theorem, to gradually simplify the circuit first, then the input part of experiment circuit would be changed as shown in Fig. 1. By analyzing the circuit, for the feedback path with a 100k Ω resistor of such large resistance relatively to R b of 1k Ω or even up to 10k Ω , so there should be just little amount of current being able to go through 100k Ω resistor, instead mainly flow through the 1k Ω resistor, then the 100k Ω resistor could be eliminated so that R a and R b would act as a voltage divider, thereof, the experimental circuit should be Voltage mixing Voltage sampling, and for the feedback circuit, it could be taken as in series-shunt mode shown in Fig. 2, so the calculation would be processed with y parameter. Fig. 1 The input part of circuit after transformation with Thévenin's (T) theorem and Norton’s (N) theorem Fig. 2 Shunt-shunt mode for feedback circuit 2 22 1 21 2 2 12 1 11 1 v y v y i v y v y i 5 21 1 5 11 10 1 10 1 y y 1 5 22 5 12 10 1 10 1 y y Thereof, the feedback gain β would be attained as y 12 , being -10 -5 V/A. And the experimental circuit would be expressed as shown in Fig. 3, and the circuit A in Fig. 3 would be constructed as Fig. 4, (T) (N)

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Lab_1_DA828447 - ELEC 321 Laboratory Report of Applied...

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