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Feedback and Oscillator Circuits. 2 of 28. 4 types of feedback. Voltage-series. Current-series. Voltage-shunt. Current-shunt ...
Feedback and Oscillator Circuits

1.0

Gain, input/output impedance, frequency response, noise, linearity

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Feedback and Oscillator Circuits

4 types of feedback Voltage-series Current-series Voltage-shunt Current-shunt

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Feedback and Oscillator Circuits

Feedback Amplifier Types

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Feedback and Oscillator Circuits

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Feedback and Oscillator Circuits

Voltage-Series Feedback

Vo = A*Vi = A(Vs – Vf) = A*Vs – A*Vf = A*Vs – A(βA)Vo (1 + βA)Vo = A*Vs Vo/Vs = A/(1 + βA)

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Feedback and Oscillator Circuits

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Voltage-Series Vo/Vi

Voltage-Shunt Vo/Ii

Current-Series Io/Vi

Current-Shunt Io/Ii

Gain w/o

A

Feedback

β

Vf/Vo

If/Vo

Vf/Io

If/Io

Gain with

Af

Vo/Vs

Vo/Is

Io/Vs

Io/Is

Feedback and Oscillator Circuits

Voltage-Series – with input and output resistances

Voltage-series feedback - Avf, Zif, Zof Avf = Vo/Vs Vo

= A*Vi

Vi

= Vs – Bf*Vo

Vo

= A*(Vs – Bf*Vo)

Vo(1 + A*Bf) Vo/Vs

= A*Vs

= A/(1 + A*Bf)

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Feedback and Oscillator Circuits

Zif = Vs/Is Vs – Vi – Bf*Vo = 0 Vi

= Is*Zi

Vo

= A*Vi

so, Vs – Is*Zi – Bf*A*Is*Zi = 0 Vs/Is = Zi(1 + Bf*A) Zof Disconnect RL and replace with Vx Zof = Vx/Ix Vx = Ix*Zo + A*Vi Vi

= -Vf

= -B*Vx

Vx = Ix*Zo + A(-B*Vx) Vx(1 + BA) = Ix*Zo Zof = Vx/Ix = Zo/(1 + BA)

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Feedback and Oscillator Circuits

Voltage-Series

Voltage-Series

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Feedback and Oscillator Circuits

Current-Series Common-emitter amplifier with an emitter resistor.

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Feedback and Oscillator Circuits

Voltage-shunt feedback

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Feedback and Oscillator Circuits

Voltage-Shunt

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Feedback and Oscillator Circuits

Current-series feedback

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Feedback and Oscillator Circuits

Current-shunt feedback

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Feedback and Oscillator Circuits

Zif

= Vs/Is

Vs

= Ii*Zi

Is

= Ii + B*Io = Ii + B*A*Ii

Is

= (Vs/Zi)(1 + BA)

Vs/Is = Zi/(1 + BA) Now disconnect RL and replace with Vx Realize that Zo is in parallel with the A*Ii = Io source, Zof = Vx/Ix Vx

= (Io + Ix)*Zo

A*Ii – Vx/Zo = Io = - Ix A*(-B*-Ix) – Vx/Zo = -Ix (B*A + 1)Ix = Vx/Zo Zf

=

Vx/Ix

= Zo(1 + B*A)

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Feedback and Oscillator Circuits

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Feedback and Oscillator Circuits

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Feedback and Oscillator Circuits

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Determine the following, a) The frequency of this oscillator is 400 kHz. What is the value of the capacitor, C ?

a) f = 1.44/(RA + 2RB)C C = 0.16nF b) T(high) = 1.1RA*C C = 4.24nF

b) This single shot has a pulse width of 35µs. RA = 7.5K. What is the value of the capacitor, C ?

Feedback and Oscillator Circuits

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Feedback and Oscillator Circuits

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