Electronics & Comm. Lab

Transcription

1 Course name Electronics & Comm. Lab Lecture 1 Dr. Bedir B. Yousif bedir.yousif@gmail.com

2 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 marks 2 Experiments execution 20 % =10 marks 3 Lectures(Reports+quiz+presents) 20 % = 10 marks 4 Final Practical +oral exam 40 % = 20 marks Bedir yousif

3 Contents Exp.1- Oscillators and Multivibrators Exp2: RC- coupled Amplifier Exp3- Amplifier Troubleshooting Exp.4 Push-pull power amplifier Exp. 5- AM and FM (modulator and demodulator) Exp. 6- ADC and DAC Exp. 7- Microwave Exp. Bedir yousif

4 Exp.1- Oscillators and Multivibrators Bedir yousif

5 Objectives After 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

6 Summary of Theory First 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. FB 1. Higher input impedance. 2. Better stabilized voltage gain. 3. Improved frequency response. 4. Lower output impedance. 5. Reduced noise. 6. More linear operation.

7 FEEDBACK CONNECTION TYPES 1. Voltage-series feedback 2. Voltage-shunt feedback 3. Current-series feedback 4. Current-shunt feedback 1

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11 Summary of Gain, Feedback, and Gain with Feedback

12 Effect of Feedback Connection on Input and Output Impedance

13 OSCILLATORs An oscillator is a circuit that produces a periodic waveform on its output with only the dc supply voltage as an input (DC- bias). The output voltage can be either sinusoidal or nonsinusoidal, depending on the type of oscillator.

14 OSCILLATORs Positive Feedback is used in some oscillators Positive 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

15 OSCILLATORs In 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

16 OSCILLATORs Conditions for Oscillation Two 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).a cl

17 OSCILLATORs 1- 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.

18 OSCILLATORs 1- 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

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

20 2- Explain the purpose of oscillator in Figure and Drive an expression of frequency oscillation and the value of f 0?

21 Exam 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 R 1 = 10 kω, R 2 = 20 kω, and C 1 = C 2 = 1 nf. 3- What are the differences between Wien bridge oscillator, Switch-integrator oscillator and multivibrator oscillator?

22 2-Switch integrator oscillator A Practical Triangular-Wave Oscillator and square-wave oscillator also A triangular-wave oscillator using two op-amps (1- comparator 2- Integrator)

23 2-Switch integrator oscillator A 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.

24 2-Switch integrator oscillator o/p signals of oscillator

25 2-Switch integrator oscillator Determine the frequency of oscillation of the circuit in Figure. To what value must R1 be changed to make the frequency 20 khz?

26 3- Multivibrator Bistable, monostable, and astable devices called multivibration devices

27 Thank You