Lecture #14 Feedback Amplifiers
Instructor: Dr. Ahmad El-Banna
Benha University Faculty of Engineering at Shoubra
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ECE-322 Electronic Circuits (A)
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Agenda
FB Amplifiers Structure
Different Topologies
Examples
Practical Feedback Circuits 2
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FEEDBACK AMPLIFIER BASICS 3
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Feedback Amplifier
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• Block diagram of a typical feedback amplifier
• Types: 1. Negative feedback. 2. Positive feedback.
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Feedback Amplifier
• Depending on the relative polarity of the signal being fed back into a circuit, one may have negative or positive feedback.
• Positive feedback drives a circuit into oscillation as in various types of oscillator circuits.
• Negative feedback results in decreased voltage gain, for which a number of circuit features are improved.
• Some improvements of negative feedback are : 1. Higher input impedance. 2. Lower output impedance. 3. Better stabilized voltage gain. 4. Improved frequency response. 5. Reduced noise. 6. More linear operation.
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FEEDBACK CONNECTION TYPES
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1. Voltage-series feedback 2. Voltage-shunt feedback
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FEEDBACK CONNECTION TYPES..
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3. Current-series feedback 4. Current-shunt feedback
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Parameters improvement
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Effect of feedback on gain:
Parameters improvement ..
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FEEDBACK CONNECTION TYPES…
• Series feedback connections tend to increase the input resistance, whereas shunt feed-back connections tend to decrease the input resistance.
• Voltage feedback tends to decrease the output impedance, whereas current feedback tends to increase the output impedance.
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Example
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Practical Feedback Circuits
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Voltage-Series Feedback
Voltage-Series Feedback circuit
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Current-Series Feedback circuit
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Current-Series Feedback circuit
Example
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• Calculate the voltage gain of the shown circuit.
• For more details, refer to:
• Chapter 14 at Boylestad, Electronic Circuits and Devices,11th edition.
• The lecture is available online at:
• http://bu.edu.eg/staff/ahmad.elbanna-courses/11966
• For inquires, send to:
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