• RSS
  • Delicious
  • Digg
  • Facebook
  • Twitter
  • Linkedin
  • Youtube

You need to upgrade your Flash Player to version 10 or newer.

Showing posts with label Feedback Amplifier:. Show all posts
Showing posts with label Feedback Amplifier:. Show all posts

Gain with feedback

Posted by AJ On Wednesday, 10 July 2013 0 comments

• Gain without feedback is A
• Feedback factor β

• Gain with feedback is (1+A β)

Voltage series feedback
• With zero feedback then Vf=0 the voltage gain of amplifier stage is
A=Vo/Vs=Vo/Vi
• If feedback of Vf is connected then,
Vi=Vs-Vf
Vo=AVi=A(Vs-Vf)=AVs-AVf=A(Vs-A(βVo)
Then, (1+ βA)Vo=AVs
Overall gain with feedback is
Af=Vo/Vi=A/(1+A β)
This shows that gain of feedback has reduced by factor (1+A β)
Voltage shunt feedback
• Af=Vo/Is=A Ii / (Ii+If)=AIi/(Ii+ βAIi)
• Af=A/(1+ βA)
Input impedance with FB
• Ref to fig(1)
Ii=Vi/Zi=(Vs-Vf) / Zi = (Vs- βVo) / Zi
Ii Zi= Vs- βAVi
Vs=Ii Zi+ β A Vi = Ii Zi+ β A Ii Zi
Zif = Vs/Ii=Zi+(βA)Zi=Zi(1+ βA)

Labels: ,

Feedback connection types

Posted by AJ On 0 comments

Feedback connection types
• Voltage series feedback
• Voltage shunt feedback
• Current series feedback
• Current shunt feedback
Ø Here voltage refers to small part of voltage as input to the feedback network
Ø Current refers to tapping some part of output current through feedback
network.
Ø Series refers to connecting feedback signal in series with the input signal
voltage.
Ø Shunt refers to connecting feedback signal in shunt with the input signal
voltage
Ø Series feedback connections increases the input resistance

Ø Shunt feedback connections decreases the input resistance.

Voltage series feedback Af=Vo/Vs

 Voltage shunt feedback

 Current series feedback

 Current shunt feedback



Labels: ,

Feedback concepts

Posted by AJ On 0 comments

• Depending on the relative polarity of fed back signal in to the circuit, there
are two types of feedback
> Negative feedback
> Positive feedback
Negative feedback results in Reduced gain
Positive feedback are used in oscillators.

Feedback amplifier
Negative feedback circuits
• Reduces the gain
• Increases input impedance
• Better stabilized frequency response
• Lower output impedance
• Reduced noise
• More linear operation
Feedback connection types
• Voltage series feedback
• Voltage shunt feedback
• Current series feedback
• Current shunt feedback
Ø Here voltage refers to small part of voltage as input to the feedback network
Ø Current refers to tapping some part of output current through feedback
network.
Ø Series refers to connecting feedback signal in series with the input signal
voltage.
Ø Shunt refers to connecting feedback signal in shunt with the input signal
voltage
Ø Series feedback connections increases the input resistance
Ø Shunt feedback connections decreases the input resistance.

Labels: ,