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Lecture 15 16

1. Feedback advantages

2. feedback disadvantages3 . Feedback topologies

Usman JavaidLecturer

Electrical Engineering Department

CIIT Islamabad


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Feedback advantages

Noise sensitivity• Noise ?


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Gain sensitivity

CONCLUSION

Percentage change in closed loop

Gain is less than the percentage

Change in open loop gain by a

Factor of (1 + AB )


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Ideal Feedback topologies


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Output impedance


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Series-shunt configuration


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Finding Input impedance


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Finding output impedance


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Series-series Feedback topology


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Shunt-shunt configuration


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Summary


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Lecture 17

1 . Feedback topologies

2. op-amp Series Shunt feedback3. op-amp shunt series feedback

Usman JavaidLecturer

Electrical Engineering Department

CIIT Islamabad


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Series shunt Feedback


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Calculating feedback transfer function

By comparison

Calculate feedback gain

By Voltage divider rule


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Calculating gain using feedback

concepts


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Input and output impedances


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Op-amp shunt-series feedback


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Feedback transfer function

For very large open loop gain it becomes

And feedback transfer function is


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Equivalent shunt-series configuration

Solve for Ifb and put in


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Equivalent Series-series configuration

Backward substitution yields


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Equivalent Model

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