Lab manual for_electronic_circuits_final_march_13_2011

ELECTRONIC CIRCUITS (802312-4)

Laboratory Manual

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

Prepared by:

Dr Iqbal Khan Dr Tarek Abdolkader Dr Waheed Younis

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

المملكة العربية السعوديةجامعة أم القرى -وزارة التعليم العالي

كلية الهندسة و العمارة اإلسالمية قسم الهندسة الكهربائية

KINGDOM OF SAUDI ARABIA Ministry of Higher Education Umm Al‐Qura University College of Engineering and Islamic Architecture Electrical Engineering Department

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

Table of Contents

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

EXPERIMENT #1 ...................................................................................... 6 FREQUENCY RESPONSE OF RC-COUPLED AMPLIFIER ............ 6 EXPERIMENT #2 .................................................................................... 13 INVERTING AND NON-INVERTING VOLTAGE AMPLIFIERS . 13 EXPERIMENT #3 .................................................................................... 22 INTEGRATOR, DIFFERENTIATOR & VOLTAGE FOLLOWER 22 EXPERIMENT #4 .................................................................................... 32 WIEN BRIDGE OSCILLATOR USING OP-AMP ............................. 32 EXPERIMENT #5 .................................................................................... 37 RC-PHASE-SHIFT OSCILLATOR USING BJT ................................ 37 MINI-PROJECT 1 ................................................................................... 41 MINI-PROJECT 2 ................................................................................... 42


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 basic

laboratory 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 kit c. Fire-exit d. telephone and emergency numbers Department/Person Telephone

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

Architecture / Secretary 0 - 5281155 / 1177

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

UQU University Service /Security 0 - 5563478 & 0 - 5562524 / x 6828 / x 6027

UQU Medical Clinic/ Emergency/ Reception 0 - 5589953/ x5658 / x5699


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 the emergency telephone number? Write it down.

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

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

6. TRUE OR FALSE: The students may be allowed to work alone in any lab area without 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 evacuate faster.


HOW TO WRITE A LAB REPORT A lab report for each experiment is to be submitted by each member (student) of a team one week after the lab session is completed. The lab report must be type written in 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 the

experiment. Summary of what you discovered. (attach the pre-lab with the lab report)

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

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

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

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


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 experiment measurements.


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 (either voltage or current) is controlled by any one of the input signal parameters. The relation should be proportional, with the constant of proportionality represents the gain of the amplifier.

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

Figure 1 RC-coupled amplifier with voltage divider biasing


The dc operating point (VCE , IC) depends on the values of RE and RC resistors. The values of VCE and IC are not independent. They are related through a linear relationship, which is called “the dc load line”. The dc operating point (Q-point) can be one of the points of the load line. Q-point must be set so that the signal variations at the input 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 open circuit. 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 is given by:

where re si the ac emitter resistance and ZE is the impedance from the emitter to ground. Referring to Fig. 2, ZE is RE1 + RE2 in parallel with XCE. PRE-LAB: The following pre-lab must be completed and submitted before the start of this experiment. 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 compare your solution with the lab experiment measurements. Analyze the circuit shown in Figure 2 to determine:

1- The dc bias point VCE , IC. 2- The voltage gain at frequencies f =100 Hz, 1 kHz, and 100 kHz 3- Assume that the capacitor CE is removed and recalculate the voltage gain

at the same frequencies given in 2.

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

Cv

e E

RAr Z

=+


EQUIPMENT REQUIRED:

• DC Power Supply • Function Generator • 2x BJT transistor (BC550) • Capacitors (3x +47μF, 2x +100μF) • Resistors 2x (100Ω, 470Ω, 1kΩ, 3.3kΩ) • Resistors 1x (10kΩ, 47kΩ, 100kΩ) • Digital Multimeter (DMM).

EXPERIMENT PROCEDURE:

1‐ Construct the circuit as shown in figure 2.

2‐ Measure the operating point of the amplifier. (disconnect AC source the Capacitors CS and CC)

VCE = _________ , VBE = _________ , VBC = _________ , IC = ________.

3- Apply constant VS of 500 mV (rms). 4- Measure Vi and VO for different frequencies ranged from 20Hz to 20kHz. Fill your

results in table-I. 5- Calculate the gain = VO/Vi , in each step.

Table-I: Input and Output Voltages.

f (Hz) Vi (Vrms) VO (Vrms) Gain . f (Hz) Vi (Vrms) VO (Vrms) Gain .

6- Plot the frequency response of the amplifier “f (Hz) against Vo/Vi” on a log-scale, using your results in table-I.

7- Now, remove the emitter by-pass capacitor CE.

8‐ Measure the operating point of the amplifier.

VCE = _________ , VBE = _________ , VBC = _________ , IC = _________ .

9- Apply constant VS of 500 mV (rms). 10- Measure Vi and VO for different frequencies ranged from 20Hz to 20kHz. Fill your

results in table-II.


11- Calculate the gain = VO/Vi , in each step.

Table-II: Input and Output Voltages without CE connected

f (Hz) Vi (Vrms) VO (Vrms) Gain . f (Hz) Vi (Vrms) VO (Vrms) Gain .

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

___________________________________ _______________ Instructor’s Signature Date




LAB REVIEW QUESTIONS:

1. Measure the operating point of the amplifier in figure 1 and compare the measured 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.


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 input voltage and level its value with a controlled amount according to the values of the resistors Ri and Rf. Assuming ideal Op-Amp, the overall (closed-loop) voltage gain is given by:

out f

vin i

V RAV R

= = −

A non-inverting amplifier is shown in Figure 2. The input is now connected to

the non-inverting terminal of the Op-Amp. The function of non-inverting amplifier is to control the level of a certain input voltage preserving its polarity. The overall voltage gain for an ideal Op-Amp is given by:

1out fv

in i

V RAV R

= = +

Figure 1 Inverting Amplifier Figure 2 Non-inverting Amplifier


PRE-LAB: The following pre-lab must be completed and submitted before the start of this experiment. 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 compare your solution with the lab experiment measurements.

1- Determine the closed-loop gain and the input impedance of the inverting amplifier of Figure 3 for Rf = 100 kΩ.

2- Repeat 1 for Ri = 1 kΩ, Rf = 10 kΩ 3- Determine the closed-loop gain and the input impedance of the non-

inverting amplifier of Figure 4 4- Repeat 1 for Ri = 1 kΩ, Rf = 10 kΩ 5- Comment on the results

Figure 3 Pre-Lab questions 1, 2 Figure 4 Pre-Lab questions 3, 4


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


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 kΩ. 3‐ Connect the Op‐Amp DC supply voltage 12±=± CCV V.

4‐ Use VS as a DC supply voltage of 500 mV. 5‐ Vary RF from 0 to 20 kΩ at constant rate. 6‐ Measure VO for each value of RF , then record it in table‐I.

7‐ Calculate the closed loop gain VO/VS 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 (kΩ) VO (V) Gain .0 5 10 15 20 25 30



b. Frequency Response:

1- Keep the circuit connected in part (a) with RF = 10 kΩ. 2- Use VS AC supply voltage (Function Generator). 3- Using DMM measure the ac voltage of VS . 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 VO 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 “Vo/Vi against f (Hz)” on a log-

scale, using your results in table-II.

Table-II: Input and Output Voltages.

f (Hz) VO (Vrms) Gain . f (Hz) VO (Vrms) Gain .




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 kΩ. 3‐ Connect the Op‐Amp DC supply voltage 12±=± CCV V.

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

7‐ Calculate the closed loop gain VO/VS 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 (kΩ) VO (V) Gain .0 5 10 15 20 25 30



b. Frequency Response:

1- Keep the circuit connected in part (a) with R = 10 kΩ. 2- Use VS AC supply voltage (Function Generator). 3- Using DMM measure the ac voltage of VS . 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 VO 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 “Vo/Vi against f (Hz)” on a log-

scale, using your results in table-II.

Table-II: Input and Output Voltages.

f (Hz) VO (Vrms) Gain . f (Hz) VO (Vrms) Gain .





1‐ Compare your results for inverting amplifier with VO/VS = ‐Rf /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?


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 amplifier for a time constant of 200µs and observe the output wave shape for a square wave input of appropriate frequency.

II. design an inverting voltage differentiator using 741 type operational amplifier for time constant of 200 µs and observe the output wave shape for a triangular wave input of appropriate frequency.

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

THEORY/BACKGROUND: I. Integrator: An op-amp integrator

simulates the integration function, which is a summing process that determines the total area 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 constant input voltage) is given by: . In other words, the output voltage will be a ramp function for a constant input voltage which is the characteristic of an integrator. Slope of the ramp is determined 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 differentiator simulates the mathematical function of differentiation. The op-amp differentiator circuit is shown here. Again it can be proven that the output voltage (for a steadily increasing input voltage) is given by: . In other words, output voltage depends upon the rate of change of input voltage

R

CVinVout

VinVout

R

C

Figure 1. Op-amp integrator circuit

Figure 2. Op-amp differentiator circuit


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

III. Voltage Follower: We know that for the non-inverting amplifier (figure 3), the output voltage is: . If in this circuit, is replaced by a short circuit and is replaced by open circuit, the output 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 certain range of frequencies.

R2

R1

VoutVin

VoutVin

Figure 3. Non-inverting amplifier

Figure 4. Voltage follower


PRE-LAB: The following pre-lab must be completed and submitted before the start of this experiment. 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 compare your solution with the lab experiment measurements. I. You want to design a 741 op-amp based integrator (figure 1), with a time constant

of 200µs. 1. First you want to choose appropriate values of R and C. If you choose R=1kΩ,

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

2. If input voltage is 3 volt constant, supply voltage for op-amp is ±15 volt, draw the 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 200µs. 1. Choose R and C of appropriate value. 2. If input voltage is a ramp function of 10kV/sec, supply voltage for op-amp is

±15 volt, draw the input and output waveforms for 5µs. 3. If input voltage is a ramp function of 50kV/sec, supply voltage for op-amp is

±15 volt, draw the input and output waveforms for 5µs. 4. If input voltage is a ramp function of 100kV/sec, supply voltage for op-amp is

±15 volt, draw the input and output waveforms for 5µs. 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?


EQUIPMENT REQUIRED:

• DC Power Supply • Function Generator • 741 IC Op-Amp • Resistors (2x 1kΩ) • Capacitors (2x 0.1μF) • 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 Vin as a Square-wave signal voltage of 5Vp-p. 5- Set the frequency to 10 kHz. 6- Use the Oscilloscope to display Vin waveform on Channel-1 and Vout

waveform on Channel-2. 7- Plot these waveforms. (neatly) 8- Change the input frequency to 1 kHz. 9- Use the Oscilloscope to display Vin waveform on Channel-1 and Vout

waveform on Channel-2. 10- Plot these waveforms. (neatly) 11- Change the frequency to 100 Hz. 12- Use the Oscilloscope to display Vin waveform on Channel-1 and Vout

waveform on Channel-2. 13- Plot these waveforms. (neatly) 14- Compare these waveforms with your waveforms from pre-lab.




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 Vin as a Triangular-wave signal voltage of 5Vp-p. 5- Set the frequency to 100Hz. 6- Use the Oscilloscope to display Vin waveform on Channel-1 and Vout

waveform on Channel-2. 7- Plot these waveforms. (neatly) 8- Change the frequency to 1 kHz. 9- Use the Oscilloscope to display Vin waveform on Channel-1 and Vout

waveform on Channel-2. 10- Plot these waveforms. (neatly) 11- Change the frequency to 10 kHz. 12- Use the Oscilloscope to display Vin waveform on Channel-1 and Vout

waveform on Channel-2. 13- Plot these waveforms. (neatly) 14- Compare these waveforms with your waveforms from pre-lab.




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 Vin. 4- Set the frequency to 10 kHz. 5- Vary Vin at constant rate, and Measure Vout for each Vin 6- Record it in table-I. 7- Calculate the Gain .

Table-I: Input and Output voltages

Vin (Vrms)

VOut

(Vrms) Gain

Vin (Vrms)

VOut

(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 Vin =1Vrms.

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

10- Measure VOut for each f.

11- Record it in table-II.

Table-II: Frequency Response.

f (Hz)

Vin (Vrms)

VOut

(Vrms) Gain

f (Hz)

Vin (Vrms)

VOut (Vrms)

Gain .

20 1500 50 2000 100 4000 150 8000 200 10000 500 15000 1000 20000


12- Calculate the gain.

13- Plot the frequency response (VOut/Vin versus f ).

14- Now set Vin =5Vrms.

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

16- Measure VOut for each f.

17- Record it in table-III.

Table-III: Frequency Response.

f (Hz)

Vin (Vrms)

VOut

(Vrms) Gain .

f (Hz)

Vin (Vrms)

VOut (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 (VOut/Vin versus f ). ___________________________________ _______________ Instructor’s Signature Date


LAB REVIEW QUESTIONS: PART I: In your report answer the following:

1- Show that CRsSV

SV

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. How the outputs are 'integrals' of the inputs?

PART II: In your report answer the following:

1- Show that CRsSVSV

in

out )()(

−= for figure 2.

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. How the outputs are 'derivatives' of the inputs?

PART III: In your report answer the following:

1- Prove that 1+=in

Out

VV .

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

3- If the amplitude of Vin is increased , will the buffer circuit give the same frequency response? (support your answer)


EXPERIMENT #4

WIEN BRIDGE OSCILLATOR USING OP-AMP

OBJECTIVE: At the completion of this experiment, students will be able to design and experimentally verify the Wien bridge oscillator using 741 type op-amp for an oscillating frequency of 5kHz. THEORY/BACKGROUND: A feedback circuit can produce sustained oscillations, if

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

R1 C2

C1R2Vin 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), the overall circuit will fulfill the requirements of self sustained oscillation and will start to

Figure 6. Frequency response of lead-lag circuit


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

R

RC

C

R1

R2

Lead-lag circuit

Voltage divider

Vout

Figure 7. Wien bridge oscillator


PRE-LAB: The following pre-lab must be completed and submitted before the start of this experiment. 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 compare your solution with the lab experiment measurements. 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.


EQUIPMENT REQUIRED:

• DC Power Supply • 741 IC Op-Amp • Resistors (2x 1kΩ, 10kΩ, variable 10kΩ, ) • Capacitors (2x 0.1μF, 2x 0.47 μF, 2x 1μF) • Digital Multi-meter • Oscilloscope.

EXPERIMENT PROCEDURE: 1- Construct the circuit as shown in figure 3. Use R and C as computed in pre-lab. Use

and (variable). 2- Connect the Op-Amp DC supply voltage 15± V. 3- Switch the DC supply ON. 4- Connect the oscilloscope to display VOut . 5- Vary the 10 kΩ 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 OSCf 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 OSCf .

C (μF)

R (k )

Measured OSCf

(Hz)

TheoreticalRC21

π=OSCf

(Hz) Error%




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

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?


EXPERIMENT #5

RC-PHASE-SHIFT OSCILLATOR USING BJT

OBJECTIVE: At the completion of this experiment, students will be able to design and experimentally verify the RC phase shift oscillator using 741 type op-amp for an oscillating frequency of 3 kHz.

THEORY/BACKGROUND: We saw in previous experiment that a feedback circuit can produce sustained oscillations, if iii. Phase shift around feedback loop is zero degree and iv. 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 (for different frequencies). There would be a certain frequency (called resonance frequency) at which the phase shift by three RC pairs would be 180 . The inverting amplifier provides a phase shift of another 180 . So the total phase shift becomes 360 or . 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 .


PRE-LAB: The following pre-lab must be completed and submitted before the start of this experiment. 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 compare your solution with the lab experiment measurements. 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 values

of , 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.


EQUIPMENT REQUIRED:

• DC Power Supply • 741 IC Op-Amp • Capacitors (3x 10nF, 3x 0.1μF, 3x 0.47μF, 1x +100μF) • Resistors (470Ω, 1kΩ, 3x 3.3 kΩ, 47kΩ, variable 1MΩ) • 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 MΩ 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 VOut. 5. Vary the 1 MΩ 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 OSCf and compare it with 3 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 OSCf .

Table-I: Frequency versus Capacitor Value

C (μF)

R (k )

Measured OSCf

(Hz)

TheoreticalRC62

1π

=OSCf

(Hz) Error%




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: check Appendix B of your text book.]

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


MINI-PROJECT 1


MINI-PROJECT 2

Lab manual for_electronic_circuits_final_march_13_2011

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