lab manual for electronic circuits final march 13 2011

8/13/2019 Lab Manual for Electronic Circuits Final March 13 2011

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ELECTRONIC CIRCUITS(802312-4)

Laboratory Manual

(Spring 2011: Term-2, 1431/1432H)

Prepared by:

Dr Iqbal KhanDr Tarek AbdolkaderDr Waheed Younis

Revised & Approved By: Electronics Sequence Committee, Date: March 1, 2011

-

KINGDOM OF SAUDI ARABIA Ministry of Higher Education

Umm AlQura University College of Engineering and Islamic Architecture

Electrical Engineering Department


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Revised & Approved By: Electronics Sequence Committee, Date: Feb. 2011 Page 1

Table of Contents

INTRODUCTION ...................................................................................... 2

LABORATORY SAFETY ..................................................................... 2HOW TO WRITE A LAB REPORT .................................................... 4HOW TO WRITE PRELAB REPORT ................................................ 5

EXPERIMENT #1 ...................................................................................... 6 FREQUENCY RESPONSE OF RC-COUPLED AMPLIFIER ............ 6

EXPERIMENT #2 .................................................................................... 13INVERTING AND NON-INVERTING VOLTAGE AMPLIFIERS . 13

EXPERIMENT #3 .................................................................................... 22INTEGRATOR, DIFFERENTIATOR & VOLTAGE FOLLOWER 22

EXPERIMENT #4 .................................................................................... 32WIEN BRIDGE OSCILLATOR USING OP-AMP ............................. 32

EXPERIMENT #5 .................................................................................... 37RC-PHASE-SHIFT OSCILLATOR USING BJT ................................ 37

MINI-PROJECT 1 ................................................................................... 41MINI-PROJECT 2 ................................................................................... 42


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INTRODUCTION

This manual has been prepared for use in the course 802312-4, Electronic Circuits. The

laboratory exercises are devised is such a way as to reinforce the concepts taught in the

lectures. Before performing the experiments, the student must be aware of the basiclaboratory safety rules for minimizing any potential dangers. The students must complete

and submit the pre-lab report of each exercise before performing the experiment. The

objective of the experiment must be kept in mind throughout the lab experiment.

LABORATORY SAFETY- Safety in the electrical engineering laboratory, as everywhere else, is a matter of

the knowledge of potential hazards, following safety regulations and precautions,

and common sense.

- Observing safety precautions is important due to pronounced hazards in any

electrical engineering laboratory.

- All the UQU Electrical Engineering Students, Teaching Assistants, Lab Engineers,

and Lab technicians are required to be familiar with the LABORATORY SAFETY

GUIDELINES FOR THE UQU ELECTRICAL ENGINEERING

UNDERGRADUATE LAB AREAS published on the department web-page.

- Practice electrical safety at all times while constructing, analyzing and

troubleshooting circuitry.- Do not accompany any drinks or water with you inside the Lab.

- If you observed an electrical hazard in the lab area NOTIFY THE

INSTRUCTOR/LAB ASSISTANT IMMEDIATELY!

- Acquaint yourself with the location of the following safety items within the lab:a. fire extinguisher

b. first aid kitc. Fire-exitd. telephone and emergency numbersDepartment/Person Telephone

Fire-Department Emergency 0 - 998Dean College of Engineering & Islamic

Architecture / Secretary 0 - 5281155 / 1177

EE Department Chair / Secretary 1024 / 1203Dean of Students Affairs: 0 - 5561916

UQU University Service /Security 0 - 5563478 & 0 - 5562524 / x 6828 / x6027UQU Medical Clinic/ Emergency/

Reception 0 - 5589953/ x5658 / x5699


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LABORATORY SAFETY REVIEW QUESTIONS:

1. YES OR NO: Have you read the Laboratory Safety Guidelines for the UQU Electrical Engineering Undergraduate Lab Areas ?

2. What should you do if an emergency situation occurs in the laboratory?

3. In the event of a fire, police, or medical emergency do you know theemergency telephone number ? Write it down.

4. TRUE OR FALSE : There is an increased risk of electric shock if you enterthe lab area bare feet .

5. TRUE OR FALSE : There is no increased risk of electric shock and theequipment is not affected in any way if food and drinks are allowed in the labarea.

6. TRUE OR FALSE : The students may be allowed to work alone in any lab areawithout the supervision of Teaching Assistant (TA) or Course Professor.

7. Fill in the blanks: a. Voltages above ________ Vrms AC are dangerous.

b. Voltages above ________ DC are dangerous.

8. TRUE OR FALSE: In the event of fire emergency use elevator to evacuatefaster.


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HOW TO WRITE A LAB REPORT

A lab report for each experiment is to be submitted by each member (student) of ateam one week after the lab session is completed. The lab report must be type writtenin the MSWord (Times-Roman 12 font) format and it must contain the following:

1. Cover page containing:

Electronic Circuits 802312-4 Experiment #______

Experiment Title: _________________________________

Group #: ___________

Your Name: ________________ & I.D. #: _________________

2. Objectives : Not copied from the lab manual

3. Specifications of Equipment Used :

4. Procedure : Steps you did in the lab. It is not copied from the lab manual

5. Block Diagram or Circuit Diagram should be included

6. Result or Analysis : Compare the Pre-lab results with those obtained in theexperiment. Summary of what you discovered. (attach the pre-lab with the labreport)

7. Answers to Questions: Answer to observation questions in the lab experiment,lab review questions and lab safety review questions at the end of theexperiment in a written form (MSWord document)

8. Conclusion: The conclusions based on the experiment and other observationsmust be clearly discussed in the laboratory report.

9. Remarks or Comments: You may write your comments regarding yourexperience of each lab experiment.

(The laboratory report will be graded for content and written English)


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HOW TO WRITE PRELAB REPORT

Pre-lab report must be completed and submitted before the start of each experiment.The pre-lab report is graded and is part of your lab grades.

The Pre-lab should be in the following format:

1. Cover page containing:

- Electronic Circuits 802213-4 Experiment #______- Experiment Title: _________________________________- Group #: ___________

- Your Name: ________________ & I.D. #: _________________

2. Solution of Pre-Lab Questions in MSWord, New Times Roman, Font: 12 ,if the solution is descriptive, otherwise hand written solution is also

appropriate.

You may need a copy of this pre-lab to compare your solution with the lab experimentmeasurements.


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EXPERIMENT #1

FREQUENCY RESPONSE OF RC-COUPLED AMPLIFIER

OBJECTIVE:

At the completion of this experiment, students will be able to: I. demonstrate the frequency response of single-stage amplifier.

II. describe the effect of the emitter by-pass capacitor.

BACKGROUND:

An amplifier is a device in which one of the output signal parameters (eithervoltage or current) is controlled by any one of the input signal parameters. The relationshould be proportional, with the constant of proportionality represents the gain of theamplifier.

RC coupled amplifier is a common-emitter transistor amplifier configuration(see Figure 1). The amplifier given in Figure 1 is biased using potential divider biasingcircuit. Capacitor elements are used for the coupling of different stages of theamplifier. The resistor RE is used for bias stabilization

Figure 1 RC-coupled amplifier with voltage divider biasing


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The dc operating point ( V CE , I C) depends on the values of RE and RC resistors.The values of V CE and I C are not independent. They are related through a linearrelationship, which is called the dc load line. The dc operating point (Q-point) can beone of the points of the load line. Q-point must be set so that the signal variations at theinput terminal are amplified and accurately reproduced at the output terminal.

The capacitors in the circuit determine the frequency response of the amplifier.For dc bias, the reactance of these capacitors is infinitely high, so they act as an opencircuit. This prevents the change of dc bias point due to adjacent stages. Sometimes, a

by-pass capacitor is put in parallel with the emitter resistance RE. The ac voltage gain isgiven by:

where r e si the ac emitter resistance and Z E is the impedance from the emitter toground. Referring to Fig. 2, Z E is R E1 + R E2 in parallel with X CE .

PRE-LAB:

The following pre-lab must be completed and submitted before the start of thisexperiment. The pre-lab is graded and is part of your lab grades.Solve the following exercises on separate sheets of paper and submit your solution

before the start of the lab experiment. You may need a copy of this pre-lab to compareyour solution with the lab experiment measurements.

Analyze the circuit shown in Figure 2 to determine:1- The dc bias point V CE , I C. 2- The voltage gain at frequencies f =100 Hz, 1 kHz, and 100 kHz

3-

Assume that the capacitor C E is removed and recalculate the voltage gainat the same frequencies given in 2.

Figure 2 : Single-Stage Amplifier with by-pass capacitor.

C v

e E

R A

r Z =

+


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11- Calculate the gain = V O /V i , in each step.

Table-II: Input and Output Voltages without C E connected

f (Hz) V i (Vrms ) V O (Vrms ) Gain . f (Hz) V i (Vrms ) V O (Vrms ) Gain .

12- Plot the frequency response of your result in table-II on a log-scale.

___________________________________ _______________Instructors Signature Date


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LAB REVIEW QUESTIONS:

1. Measure the operating point of the amplifier in figure 1 and compare themeasured values with those obtained theoretically.

2. What is the effect of the by-pass capacitor of the amplifier in figure 2?3. From the results in table-I, find the cut-off frequency.4. From the results in table-II, find the cut-off frequency.


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EXPERIMENT #2

INVERTING AND NON-INVERTING VOLTAGE AMPLIFIERS

OBJECTIVE:

At the completion of this experiment, students will be able to: I. Design an inverting voltage amplifier using 741 type operational amplifier for

a gain of -10 and to measure its frequency response.II. Design a non-inverting voltage amplifier using 741 type operational amplifier

for a gain of 11 and to measure its frequency response.

BACKGROUND:

An inverting amplifier is shown in Figure 1. Its function is to invert inputvoltage and level its value with a controlled amount according to the values of theresistors Ri and Rf . Assuming ideal Op-Amp, the overall (closed-loop) voltage gain isgiven by:

out f v

in i

V R A

V R= =

A non-inverting amplifier is shown in Figure 2. The input is now connected tothe non-inverting terminal of the Op-Amp. The function of non-inverting amplifier isto control the level of a certain input voltage preserving its polarity. The overallvoltage gain for an ideal Op-Amp is given by:

1out f vin i

V R A

V R= = +

Figure 1 Inverting Amplifier Figure 2 Non-inverting Amplifier


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EQUIPMENT REQUIRED: 2x DC Power Supply Function Generator 741 IC Op-Amp Resistors (1k , 10k , 100k ) Digital multi-meter

EXPERIMENT PROCEDURE:

PART I: Inverting Amplifier:

a. Inverting DC gain

Figure 5 : Inverting Amplifier .

1- Construct the circuit as shown in figure 5.2- Use R = 1 k .3 Connect the OpAmp DC supply voltage 12= CC V V.

4 Use V S as a DC supply voltage of 500 mV. 5 Vary RF from 0 to 20 k at constant rate.

6

Measure V O

for

each

value

of

RF

, then

record

it

in

table

I.

7 Calculate the closed loop gain V O/ V S in each step in table I. 8 Plot Gain versus RF using proper scale using data in table I. 9 Determine the value of RF at which the gain is 10.

Table I: Gain at different values of RF for Inverting Amplifierof Fig. 5.

RF (k ) V O (V) Gain .0 5

10 15 20 25 30



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b. Frequency Response:

1- Keep the circuit connected in part (a) with RF = 10 k .2- Use V S AC supply voltage (Function Generator).3- Using DMM measure the ac voltage of V S . Vary the amplitude until the

reading of DMM gives 500 mV(rms).4- Vary the frequency ( f ) from 20 to 20kHz at constant rate.5- Measure V O for each f , then record it in table-II.6- Calculate the Gain , then record it in table-II.7- Plot the frequency response of the amplifier V o /V i against f (Hz) on a log-

scale, using your results in table-II.

Table-II: Input and Output Voltages.

f (Hz) V O (Vrms ) Gain . f (Hz) V O (Vrms ) Gain .



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PART II: Non inverting Amplifier:

a. Non inverting DC gain

Figure 6 : Non-inverting Amplifier .

1- Construct the circuit as shown in figure 6.2- Use RF = 100 k .3 Connect the OpAmp DC supply voltage 12= CC V V.

4 Use V S as a DC supply voltage of 500 mV. 5 Vary R from 0 to 20 k at constant rate. 6 Measure V O for each value of R , then record it in table I.

7 Calculate the closed loop gain V O/ V S in each step in table I. 8 Plot Gain versus R using proper scale using data in table I. 9 Determine the value of R at which the gain is 11.

Table I: Gain at different values of resistance R for Non inverting Amplifier of Fig. 6.

R (k ) V O (V) Gain .0 5

10 15 20 25 30



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b. Frequency Response:

1- Keep the circuit connected in part (a) with R = 10 k .2- Use V S AC supply voltage (Function Generator).3- Using DMM measure the ac voltage of V S . Vary the amplitude until the

reading of DMM gives 500 V(rms).4- Vary the frequency ( f ) from 20 to 20kHz at constant rate.5- Measure V O for each f , then record it in table-II.6- Calculate the Gain , then record it in table-II.7- Plot the frequency response of the amplifier V o /V i against f (Hz) on a log-

scale, using your results in table-II.

Table-II: Input and Output Voltages.

f (Hz) V O (Vrms ) Gain . f (Hz) V O (Vrms ) Gain .



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1 Compare your results for inverting amplifier with V O /V S = R f /R . Find the percentage error.

2 Compare your results for non inverting amplifier with 1O f S

V RV R

= + .

Find the percentage error.

3 What is the maximum output voltage that can be obtained?

4 Determine the cut off frequency of the obtained frequency responses.

5 If the value of the resistor R is increased, what will happen?

6 If the value of the resistor RF is increased, what will happen?


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EXPERIMENT #3

INTEGRATOR, DIFFERENTIATOR & VOLTAGE FOLLOWER

OBJECTIVE:

At the completion of this experiment, students will be able to

I. design an inverting voltage integrator using 741 type operational amplifierfor a time constant of 200s and observe the output wave shape for a squarewave input of appropriate frequency.

II. design an inverting voltage differentiator using 741 type operationalamplifier for time constant of 200 s and observe the output wave shape fora triangular wave input of appropriate frequency.

III. study the voltage follower constructed from 741 op-amp.

THEORY/BACKGROUND:

I. Integrator: An op-amp integratorsimulates the integration function, which isa summing process that determines the totalarea under the curve of a function. The op-amp integrator circuit is depicted here. It

can be shown (section 13.3 of the text book) that the output voltage (for a constantinput voltage) is given by: .

In other words, the output voltage will be a ramp function for a constant inputvoltage which is the characteristic of an integrator. Slope of the ramp isdetermined by magnitude of input voltage and RC (also called the time constant).Maximum value of the ramp is determined by the supply voltage of the op-amp.

II. Differentiator: An op-amp differentiatorsimulates the mathematical function ofdifferentiation. The op-amp differentiatorcircuit is shown here. Again it can be

proven that the output voltage (for asteadily increasing input voltage) is given

by:.

In other words, output voltage dependsupon the rate of change of input voltage

R

CVinVout

VinVout

R

C

Figure 1. Op-amp integrator circuit

Figure 2. Op-amp differentiator circuit


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( ) which is the characteristic of the differentiator. Magnitude of the outputvoltage is determined by the slope of the input voltage and RC (also called thetime constant). Maximum value of the output voltage is determined by the supplyvoltage of the op-amp.

III. Voltage Follower: We know that for the non-inverting amplifier (figure 3), theoutput voltage is:

.

If in this circuit, is replaced by a short

circuit and is replaced by open circuit, theoutput voltage become

and the new circuit will be called voltage

follower (figure 4).In voltage follower, the output voltage is same as the input voltage for a certainrange of frequencies.

R2

R1

VoutVin

VoutVin

Figure 3. Non-inverting amplifier

Figure 4. Voltage follower


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PRE-LAB:



I. You want to design a 741 op-amp based integrator (figure 1), with a time constantof 200s.1. First you want to choose appropriate values of R and C. If you choose R=1k ,

what should be the value of C? If C is chosen as 0.01 F, what should be thevalue of R?

2. If input voltage is 3 volt constant, supply voltage for op-amp is 15 volt, drawthe input and output waveforms for 5 mSec. [All the plots should be made on

proper graph paper with correct units and scales on both axis.]3. If input voltage is 1 volt constant, supply voltage for op-amp is 15 volt, draw

the input and output waveforms for 5 mSec.4. If input voltage is 1 volt constant, supply voltage for op-amp is 10 volt, draw

the input and output waveforms for 5 mSec.5. If the input voltage is a square wave of 5 volt peak-to-peak and 10kHz, supply

voltage for op-amp is 15 volt, draw the input and output waveforms.6. If the input voltage is a square wave of 5 volt peak-to-peak and 1kHz, supply

voltage for op-amp is 15 volt, draw the input and output waveforms.7. If the input voltage is a square wave of 5 volt peak-to-peak and 100Hz, supply

voltage for op-amp is 15 volt, draw the input and output waveforms.II. You want to design a 741 op-amp based differentiator (figure 2), with a time

constant of 200s.

1. Choose R and C of appropriate value.2. If input voltage is a ramp function of 10kV/sec, supply voltage for op-amp is15 volt, draw the input and output waveforms for 5s.

3. If input voltage is a ramp function of 50kV/sec, supply voltage for op-amp is15 volt, draw the input and output waveforms for 5s.

4. If input voltage is a ramp function of 100kV/sec, supply voltage for op-amp is15 volt, draw the input and output waveforms for 5s.

5. If the input voltage is a triangular waves of 5 volt peak-to-peak and 100Hz,supply voltage for op-amp is 15 volt, draw the input and out waveforms.

6. If the input voltage is a triangular waves of 5 volt peak-to-peak and 1kHz,supply voltage for op-amp is 15 volt, draw the input and out waveforms.

7. If the input voltage is a triangular waves of 5 volt peak-to-peak and 10kHz,supply voltage for op-amp is 15 volt, draw the input and out waveforms.

III. In a voltage follower, if the output voltage is same as the input voltage, what is the benefit of it? Where the voltage follower is used?


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EQUIPMENT REQUIRED:

DC Power Supply Function Generator 741 IC Op-Amp

Resistors (2x 1k ) Capacitors (2x 0.1 F) Digital Multimeter Oscilloscope.


PART I: Integrator:

1- Construct the circuit as shown in figure 1.2- Use R and C as computed in pre-lab.3- Connect the Op-Amp DC supply voltage as 15 V.4- Use V in as a Square-wave signal voltage of 5Vp-p.5- Set the frequency to 10 kHz.6- Use the Oscilloscope to display V in waveform on Channel-1 and V out

waveform on Channel-2.7- Plot these waveforms. (neatly)8- Change the input frequency to 1 kHz.9- Use the Oscilloscope to display V in waveform on Channel-1 and V out

waveform on Channel-2.10- Plot these waveforms. (neatly)11- Change the frequency to 100 Hz.12- Use the Oscilloscope to display V in waveform on Channel-1 and V out

waveform on Channel-2.13- Plot these waveforms. (neatly)14- Compare these waveforms with your waveforms from pre-lab.


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PART II: Differentiator:

1- Construct the circuit as shown in figure 2.2- Use R and C as computed in pre-lab.3- Connect the Op-Amp DC supply voltage 15 V.4- Use V in as a Triangular-wave signal voltage of 5Vp-p.5- Set the frequency to 100Hz.6- Use the Oscilloscope to display V in waveform on Channel-1 and V out

waveform on Channel-2.7- Plot these waveforms. (neatly)8- Change the frequency to 1 kHz.9- Use the Oscilloscope to display V in waveform on Channel-1 and V out

waveform on Channel-2.10- Plot these waveforms. (neatly)11- Change the frequency to 10 kHz.12- Use the Oscilloscope to display V in waveform on Channel-1 and V out

waveform on Channel-2.13- Plot these waveforms. (neatly)14- Compare these waveforms with your waveforms from pre-lab.


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PART III: Voltage Follower (Buffer):

1- Construct the circuit as shown in figure 3.2- Connect the Op-Amp DC supply voltage 15 V.3- Use an AC source for V in .4- Set the frequency to 10 kHz.5- Vary V in at constant rate, and Measure V out for each V in 6- Record it in table-I.7- Calculate the Gain .

Table-I: Input and Output voltages

V in (Vrms )

V Out (Vrms )

Gain V in

(Vrms ) V Out (Vrms )

Gain .

0.0 3.0 0.5 3.5 1.0 4.0 1.5 4.5 2.0 5.0 2.5 5.5

8- Set V in =1Vrms.

9- Vary frequency from 20 to 20kHz at constant rate.

10- Measure V Out for each f .

11- Record it in table-II.

Table-II: Frequency Response.

f (Hz)

V in (Vrms )

V Out (Vrms )

Gain f

(Hz) V in

(Vrms ) V Out

(Vrms ) Gain .

20 1500

50 2000 100 4000 150 8000 200 10000 500 15000

1000 20000


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12- Calculate the gain.

13- Plot the frequency response ( V Out /V in versus f ).

14- Now set V in =5Vrms.

15- Vary frequency from 20 to 20kHz at constant rate.16- Measure V Out for each f .

17- Record it in table-III.

Table-III: Frequency Response.

(Hz) V in

(Vrms ) V Out

(Vrms ) Gain .

f (Hz)

V in (Vrms )

V Out (Vrms )

Gain .

20 1500 50 2000

100 4000 150 8000 200 10000 500 15000

1000 20000

18- Calculate the gain.

19- Plot the frequency response ( V Out /V in versus f ).



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PART I: In your report answer the following:

1- Show thatCRsS V

S V

in

out

1

)()(

= for figure 1.

2- If the input is a sinusoidal signal, what do you expect the output to be?How will it differ from the input waveform.

3- Explain the relationship between the input and output waveforms. Howthe outputs are 'integrals' of the inputs?

PART II: In your report answer the following:

1- Show that C RsS V

S V

in

out )()(

= for figure 2.

2- If the input is a sinusoidal signal, what do you expect the output to be? Howwill it differ from the input waveform.

3- Explain the relationship between the input and output waveforms. How theoutputs are 'derivatives' of the inputs?

PART III: In your report answer the following:

1- Prove that 1+=in

Out

V

V .

2- From your experimental results, calculate the cut-off frequency.

3- If the amplitude of V in is increased , will the buffer circuit give the samefrequency response? (support your answer)


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EXPERIMENT #4

WIEN BRIDGE OSCILLATOR USING OP-AMP

OBJECTIVE:

At the completion of this experiment, students will be able to design andexperimentally verify the Wien bridge oscillator using 741 type op-amp for anoscillating frequency of 5kHz.

THEORY/BACKGROUND:

A feedback circuit can produce sustained oscillations, if

i. Phase shift around feedback loop is zero degree andii. The voltage gain around the feedback loop is one.

R1 C2

C1

R2Vin Vout

Figure 5. The lead-lag circuit

Consider the lead lag circuit (figure 1). In this circuit, the output voltage peaks to one-

third of the input voltage (figure 2) i.e. and the phase shift through the

circuit is going to be zero degree at a particular resonance frequency given by

(where and ).

If this circuit is used in the positive feedback loop of an op-amp and a voltage divider(with a gain of 3) is used in the negative feedback loop as shown below (figure 3), theoverall circuit will fulfill the requirements of self sustained oscillation and will start to

Figure 6. Frequency response of lead-lag circuit


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oscillate. Finally, in order to have the required gain for the negative feedback loop, weneed to have .

R

RC

C

R1

R2

Lead-lag circuit

Voltage divider

Vout

Figure 7. Wien bridge oscillator


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PRE-LAB:



1. For the lead-lag circuit of figure 1, prove that the transfer function will be

2. Using above transfer function, show that the magnitude of the transfer

function will be 1/3 when or .3. Using the same transfer function, show that the phase angle of the transfer

function will be zero at or .4. For the non-inverting amplifier portion of the op-amp of figure 3, show

that its gain will be 3 if . 5. For the Wien bridge oscillator of figure 3, compute the values of R and C

to produce an oscillation frequency of 5kHz (try different combinations of R and C ).

6. An oscillator circuit produces output without any input. Explain how.


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EQUIPMENT REQUIRED:

DC Power Supply 741 IC Op-Amp Resistors (2x 1k , 10k , variable 10k , )

Capacitors (2x 0.1 F, 2x 0.47 F, 2x 1 F) Digital Multi-meter Oscilloscope.


1- Construct the circuit as shown in figure 3. Use R and C as computed in pre-lab. Useand (variable).

2- Connect the Op-Amp DC supply voltage 15 V.3- Switch the DC supply ON.4- Connect the oscilloscope to display V Out .5- Vary the 10 k variable resistor so that oscillation can take place, you can observe

that on display of the oscilloscope (a sine wave is generated).6- Measure the frequency of oscillation OSC f and compare it with 5 kHz.7- Try different values of R and C . Compare the computed and measured frequencies.8- Record your results in following table and calculate the percentage error relative to

theoretical OSC f .

C

(F)

R

(k )Measured OSC f

(Hz)

TheoreticalRC2

1

=OSC f

(Hz) Error%



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1. Write a short article (around one page) about the history of Wien bridgeoscillator.

2. Why the circuit shown in figure 1 is called a lead-lag circuit?3. Plot the magnitude of the transfer function verses frequency. Use the value

of R and C from pre-lab calculations. Make the plot on a semi-log graph paper. Use frequency ranges of 500 Hz to 50 kHz.

4. What should be the value of gain set by and to produce oscillations?What will happen if the gain set by and is not exactly correct?


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EXPERIMENT #5

RC-PHASE-SHIFT OSCILLATOR USING BJT

OBJECTIVE:

At the completion of this experiment, students will be able to design andexperimentally verify the RC phase shift oscillator using 741 type op-amp for anoscillating frequency of 3 kHz.

THEORY/BACKGROUND:

We saw in previous experiment that a feedback circuit can produce sustainedoscillations, ifiii. Phase shift around feedback loop is zero degree andiv. The voltage gain around the feedback loop is one.

C1 C2 C3

R1 R2 R3

Rf

Vout

Figure 8. Op-amp based phase shift oscillator

In the above circuit, each RC pair introduces a phase shift between to (fordifferent frequencies). There would be a certain frequency (called resonancefrequency) at which the phase shift by three RC pairs would be 180 . The invertingamplifier provides a phase shift of another 180 . So the total phase shift becomes 360or . It can be shown that the gain introduced by the three stages of RC circuit is

. In order to compensate for this gain and produce sustained oscillations, the gain

set by and should be 29 i.e. . When this condition is fulfilled, the

circuit will start oscillating at a frequency where

and .


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PRE-LAB:



1. For the circuit shown below, the transfer function is given by

Prove that this transfer function will be a real number if

which is called resonance frequency.

C1 C2 C3

R1 R2 R3

VoutVin

Figure 9. Three stage RC circuit used in phase-shift oscillator

2. Also show that the at resonance frequency the gain would be

3. Consider the phase-shift oscillator circuit of figure 1. Calculate the valuesof , to produce a resonance frequency of 3 kHz.

4. Calculate the value of to produce a gain of 29.5. Write a half page description of how this circuit produces sustained

oscillations.


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EQUIPMENT REQUIRED:

DC Power Supply 741 IC Op-Amp Capacitors (3x 10nF, 3x 0.1 F, 3x 0.47 F, 1x +100 F)

Resistors (470 , 1k , 3x 3.3 k , 47k , variable 1M ) Digital multi-meter Oscilloscope.


1. Construct the circuit as shown in figure 1. Use Rs and Cs as computed in pre-lab. Use the 1 M variable resistor for .

2. Connect the Op-Amp DC supply voltage 15 V.

3. Switch the DC supply ON .4. Connect the oscilloscope to display V Out .5. Vary the 1 M variable resistor so that oscillation can take place, you can

observe that on display of the oscilloscope (a sine wave is generated).6. Measure the frequency of oscillation OSC f and compare it with 3 kHz.

7. Try different values of R and C . Compare the computed and measuredfrequencies.

8. Record your results in following table and calculate the percentage errorrelative to theoretical OSC f .

Table-I: Frequency versus Capacitor Value

C(F)

R(k )

Measured OSC f

(Hz)

TheoreticalRC62

1

=OSC f

(Hz)

Error%



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1- Can we implement an RC -phase-shift oscillator with less than three sections?Why?

2- Drive the expression for transfer function given in pre-lab. [Hint: checkAppendix B of your text book.]

3- The gain of the inverting amplifier set by and should be 29. Explainwhy?


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MINI-PROJECT 1


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MINI-PROJECT 2

lab manual for electronic circuits final march 13 2011

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