Lecture #11 Feedback Circuits Instructor: Dr. Ahmad El-Banna December 2014 J-601-1448 Electronic Principals Integrated Technical Education Cluster At AlAmeeria‎ © Ahmad El-Banna

Agenda 2 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna Feedback Concepts Feedback Connection Types Practical Feedback Circuits

Simple block diagram of feedback amplifier 3 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna Some improvements are : 1. 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 TYPES 4 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna • 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.

Gain with Feedback 5 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna

Input Impedance with Feedback 6 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna

Output Impedance with Feedback 7 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna

Example 8 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna

Effects of feedback on Gain and Bandwidth 9 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna

Practical Feedback Circuits 10 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna

Using OP-Amp & Emitter follower 11 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna Check EXAMPLE 14.4

Current Series Feedback 12 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna

Voltage Shunt Feedback 13 J-601-1448 , Lec#11 , Dec 2014 © Ahmad El-Banna

• For more details, refer to: • Chapter 14, Electronic Devices and Circuits, Boylestad. • The lecture is available online at: • https://speakerdeck.com/ahmad_elbanna • For inquires, send to: • ahmad.elbanna@feng.bu.edu.eg 14 © Ahmad El-Banna J-601-1448 , Lec#11 , Dec 2014