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Feedback Amplifier Lab Report

This document summarizes an electrical engineering student's laboratory report on an experiment investigating feedback amplifiers. The student measured the characteristics of two different feedback amplifier circuit prototypes: a parallel-series configuration and a parallel-parallel configuration. For both prototypes, the student determined values for input resistance, output resistance, gain, and bandwidth both with and without feedback. The conclusions indicate that the parallel-series prototype behaved somewhat unexpectedly, while the parallel-parallel prototype results agreed with theory except for bandwidth, which decreased rather than increased with feedback.

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Angelica Wood
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179 views5 pages

Feedback Amplifier Lab Report

This document summarizes an electrical engineering student's laboratory report on an experiment investigating feedback amplifiers. The student measured the characteristics of two different feedback amplifier circuit prototypes: a parallel-series configuration and a parallel-parallel configuration. For both prototypes, the student determined values for input resistance, output resistance, gain, and bandwidth both with and without feedback. The conclusions indicate that the parallel-series prototype behaved somewhat unexpectedly, while the parallel-parallel prototype results agreed with theory except for bandwidth, which decreased rather than increased with feedback.

Uploaded by

Angelica Wood
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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ADDIS ABABA UNIVERSITY TECHNOLOGY FACULTY

ELECTRICAL AND COMPUTER ENGINEERING DEPARTMENT

COURSE NO. = ECEG-2206 EXPERIMENT -3 TITLE :- FEEDBACK AMPLIFIER

LABORATORY REPORT

BY:- ESHET TEZERA (TCR/1091/01) GROUP=2C-5

DATE OF EXPERIMENT:02/04/2010 DATE OF SUBMISSION:12/04/2010


1

OBJECTIVE
In this experiment, it has been tried to study the different types of feedback and feedback amplifiers.

EQUIPMENT

Equipment oscilloscope Function generator

No 1 1

COMPONENTS

component resistors

capacitance

transistor

type 1k 1.8k 27k 33 4.7k 5.6k 100k 47k 18k 10u 80n 0.2u BC107

No 2 1 1 1 1 1 1 1 1 1 1 1 2

THEORY
Feedback for amplifiers could be: Positive feedback generate oscillations Negative feedback to improve the amplifier features In this experiment, we are concerned with the negative feedback ones. Important features; Amplifier gain(A)= Vo/V1 Feedback gain(B) = Vf/Vo Feedback amplifier gain(Asp) = Vo/Vin The sacrifice factor(s) = A/Asp Asp = A/(1+BA) S = Vin/(Vin-Vf) Since A is about 100, Asp = 1/B

Vin mixer Vff

V1

sampling

A(amplifier)
Vo

B(feedback)

The four Amplifier feedback network prototypes;(sampling-mixing prototype) 1. 2. 3. 4. Serie- series(ss) prototype Series-parallel(sp) prototype Parallel-series(ps) prototype Parallel-parallel(pp) prototype

R1 Vi Voi Rii Voo

Rio R2 Vo

How to determine input and out put resistance, Rii =R1Vi/(Voi-Vi) and Rio = R2(Voo-Vo)/Vo 3

How to determine the half power frequency by appling square wave form

The R1C1 time constant affects the lower half power frequency while R2C2 affects the upper. Appliny square wave form we end up with what is shown below. V1 =Vo(1)

Then find the rise time(Tr) From t1=0.1RC and t2 = 2.3RC Tr = t1-t2 = 2.2RC The break frequency are given by f = 1/2RC So after combining it with rise or fall time equation the half power frequencies will be F = 0.35/Tr f=0.35/Ts , where Ts is sag or fall time

PROCEDURE
FEEDBACK TYPE 1
1.1 Setup the circuit shown;

1.2 Without supplying ac measure Vb, Ve and Vce with oscilloscope. Vb = 2v Ve = 1.4v Vce =7.2v 1.3 At f=1khz, find the input anoutput resistance in addition to this find the gain and the bandwidth. Ri=20k Ro=4.1k Av=3.33 BW=2.0532Mhz 1.4 Remove C3 and repeat step 4 Ri=20k Ro=4.6k Av=3.16 BW=2.0982Mhz

FEEDBACK TYPE 2
2.1 connect the circuit shown; RD is decade resistor and its value is such that Vce = 5v,Rd = 2M

2.2 repeat the steps from 1.2 to 1.3 I. II. Vce=5v , Ve=1v ,Vb= 1.4v Applying 1khz signal Av = 3.16 Ri= 100k Ro=5k BW =227khz

CONCLUSION
From the above demonstration, we have seen that how a PP and PS prototype feedback amplifiers work or behave. Considering the type one(PS) amplifier the change on the input resistance is very low but the output resistance has increased by a little and this result is a bit unorthodox since in theory it supposed to be the other way round. The changes that have occurred on the Av and BW is in accordance to the theory in which Av decreases and BW increase. For the feedback type two(PP) the results are mostly in agreement with the theory except that the BW has fallen.

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