Course name

Electronics & Comm. Lab

Lecture 1Dr. Bedir B. Yousif

E-mail: bedir.yousif@gmail.com

Third Year-Comm Eng. Lecture: 1 hr. /week Section : 3 hrs. /week

Subject Marks: 100 (50 works term + 50 final exam)

Students evaluation (50 Marks = 100%)

1 Experiments Reports 20 % =10 marks2 Experiments execution 20 % =10 marks3 Lectures(Reports+quiz+presents) 20 % = 10 marks4 Final Practical +oral exam 40 % = 20 marks

Bedir yousif

ContentsExp.1- Oscillators and Multivibrators

Exp2: RC- coupled Amplifier

Exp3- Amplifier TroubleshootingExp.4 Push-pull power amplifier

Exp. 5- AM and FM (modulator and demodulator)

Exp. 6- ADC and DAC

Exp. 7- Microwave Exp. Bedir yousif

Exp.1- Oscillators and

Multivibrators

Bedir yousif

ObjectivesAfter completing this experiment, you will be able to Understand the concept of feedback circuits.

•Study a typical linear oscillators.

•See how a nonlinearity is required to stabilize the gain.

•Examine a switchable-integrator oscillator.

• To Examine a typical Multivibrator based on OP- AMP

Summary of TheoryFirst oscillators based on the concept of Feedback. Depending on the relative polarity of the signal being fed back into a circuit, one may have negative (-ve. FB)or positive feedback.a number of improvements are obtained using –ve. FB1. Higher input impedance.2. Better stabilized voltage gain.3. Improved frequency response.4. Lower output impedance.5. Reduced noise.6. More linear operation.

FEEDBACK CONNECTION TYPES1. Voltage-series feedback2. Voltage-shunt feedback3. Current-series feedback4. Current-shunt feedback

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2

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Summary of Gain, Feedback, and Gain with Feedback

Effect of Feedback Connection on Input and Output Impedance

OSCILLATORs

An oscillator is a circuit that produces a periodicwaveform on its output with only the dc supplyvoltage as an input (DC- bias).The output voltage can be either sinusoidal or non-sinusoidal, depending on the type of oscillator.

OSCILLATORsPositive Feedback is used in some oscillatorsPositive feedback is characterized by the condition wherein a portion of the output voltage of an amplifier is fed back to the input with no net phase shift, resulting in a reinforcement of the output signal. This basic idea is illustrated in Figure

OSCILLATORsIn some types of amplifiers the feedback circuit shifts the phase and an inverting amplifier is required to provide another phase shift so that there is no net phase shift. This is illustrated in Figure

OSCILLATORsConditions for OscillationTwo conditions, illustrated in Figure, are required for a sustained state of oscillation:1. The phase shift around the feedback loop must be effectively 2. The voltage gain, around the closed feedback loop (loop gain) must equal 1 (unity).Acl

OSCILLATORs1- WIEN BRIDGE OSCILLATOR(sinusoidal output)Based on Wheatstone bridge.It can oscillate only at a frequency which FB has zero phase shift (this occurs only at one frequency) and loop gain equal one.

OSCILLATORs1- WIEN BRIDGE OSCILLATOR(sinusoidal output)the analysis of the bridge circuit results in

If, in particular, the values are R1 = R2 = R and C1 = C2 = C, the resulting oscillator frequency is

Report WIEN BRIDGE OSCILLATORDrive an expression for Acl = AB and prove that A=3 at oscillation frequency.

2- Explain the purpose of oscillator in Figure and Drive an expression of frequency oscillation and the value of f0?

Exam 20141- Explain the basic idea of Wien bridge oscillator circuit operation and drive an expression for the oscillation frequency? 2-Calculate the oscillation frequency of a Wien bridge oscillator circuit when R1= 10 kΩ, R2= 20 kΩ, and C1 = C2 = 1 nF. 3- What are the differences between Wien bridge oscillator, Switch-integrator oscillator and multivibrator oscillator?

2-Switch – integrator oscillatorA Practical Triangular-Wave Oscillator and square-wave oscillator also

A triangular-wave oscillator using two op-amps (1- comparator 2-Integrator)

2-Switch – integrator oscillatorA triangular-wave oscillator using two op-amps (1- comparator (ON/ off switch) 2- Integrator)(1- comparator (ON/ off switch) is +ve. FB switch so the o/p voltage +ve. or –ve.The great virtue of this type is that it has an excellent inherent amplitude control,(good amplitude stability) which acts very quickly.

Some applications needs the oscillator (i.e PWM and PPM) and with some a suitable nonlinearity, convert the triangle wave to sine wave.

2-Switch – integrator oscillatoro/p signals of oscillator

2-Switch – integrator oscillatorDetermine the frequency of oscillation of the circuit in Figure. To what value must R1 be changed to make the frequency 20 kHz?

3- MultivibratorBistable, monostable, and astable devices calledmultivibration devices

Thank You