Chapter #12: Feedback. Eng.Mohammed S. Abuwarda. Fall Semester_2017

Transcription

1 Chapter #12: Feedback Eng.Mohammed S. Abuwarda Fall Semester_2017

2 10.1. The General Feedback Structure Figure shows the basic structure of a feedback amplifier signal-flow diagram. Open-loop amplifier has gain A (x o = Ax i ). Figure 10.1: General structure of the feedback amplifier. This is a signal-flow diagram, and the quantities x represent either voltage or current signals. The College of New Jersey (TCNJ) ELC251 Electronics I Based on Textbook: Microelectronic Circuits by Adel S. Sedra ( )

3 10.1. The General Feedback Structure Output (x o ) is fed to load as well as feedback network. Feedback factor (b.) defines feedback signal (x f ). Feedback signal (x f ) is subtracted from source (x s ). This characterizes negative feedback.

4 10.1. The General Feedback Structure

5 10.1. The General Feedback Structure Equations (10.1) through (10.3) may be obtained from (10.6) and (10.7). (eq10.6) feedback signal: (eq10.7) input signal: (eq10.6) input signal: ( eq10.6) input signal: x The College of New Jersey (TCNJ) ELC251 Electronics I Based on Textbook: Microelectronic Circuits by Adel S. Sedra ( ) f Ab xi xs x f xs x 1 Ab x i i x Ab x 1 Ab Ab 1 x 1 Ab 1 x 1 Ab s s s s

6 10.3. The Four Basic Feedback Topologies Voltage Amplifiers Current Amplifiers Trans-conductance Amplifiers Trans-resistance Amplifiers

7 The Four Amplifier Types

8 Voltage Amplifiers voltage amplifiers accept input voltage and yield output voltage. VCVS Thevenin Output voltage-mixing / voltage-sampling is the topology most suitable for voltage amps. Is also known as series-shunt feedback. Provides high input resistance/low output resistance.

9 Figure 10.6: Block diagram of a feedback voltage amplifier. Here the appropriate feedback topology is series shunt. The College of New Jersey (TCNJ) ELC251 Electronics I Based on Textbook: Microelectronic Circuits by Adel S. Sedra ( )

10 Figure 10.7: Examples of a feedback voltage amplifier. All these circuits employ series shunt feedback. Note that the dc bias circuits are only partially shown. The College of New Jersey (TCNJ) ELC251 Electronics I Based on Textbook: Microelectronic Circuits by Adel S. Sedra ( )

11 Current Amplifiers current amplifier accepts input current to generate output current. CCCS Norton Source current-mixing / current-sampling topology is most suitable for current amps. Is also known as shunt-series feedback. Provides low input resistance/high output resistance.

12 Figure 10.8: (a) Block diagram of a feedback current amplifier. Here, the appropriate feedback topology is the shunt series. (b) Example of a feedback current amplifier. The College of New Jersey (TCNJ) ELC251 Electronics I Based on Textbook: Microelectronic Circuits by Adel S. Sedra ( )

13 Transconductance Amplifiers transconductance amplifier accepts input voltage and generates output current. VCCS Norton Source Output voltage-mixing / current-sampling topology is most suitable for transconductance amps. Is also known as series-series feedback. Provides high input resistance/high output resistance.

14 Figure 10.10: (a) Block diagram of a feedback transconductance amplifier. Here, the appropriate feedback topology is series series. (b) Example of a feedback transconductance amplifier. (c) Another example. The College of New Jersey (TCNJ) ELC251 Electronics I Based on Textbook: Microelectronic Circuits by Adel S. Sedra ( )

15 Transresistance Amplifiers transresistance amplifier accepts input current and generates output voltage. CCVS Thevenin Source Output current-mixing / voltage-sampling topology is most suitable for current amps. Is also known as shunt-shunt feedback. Provides low input resistance/low output resistance.

16 Figure 10.11: (a) Block diagram of a feedback transresistance amplifier. Here, the appropriate feedback topology is shunt shunt. (b), (c), and (d) Examples of feedback transresistance amplifiers. The College of New Jersey (TCNJ) ELC251 Electronics I Based on Textbook: Microelectronic Circuits by Adel S. Sedra ( )

17 Summary of Relationships for the Four Feedback-Amplifier Topologies