Why open loop op-amp have infinite gain?

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zhi_yi

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hi there, i have a question, please tell me why the open loop op-amp have the infinite gain?

is there any good free tutorials/ebook about analog signal modulations?

thank you,

zhi yi
 

Re: open loop op amp

hi zhi_yi;

in real world the gain of opamps is never infinit. but in a simple model for theoritical analysis we can consider infinit gain , or zero input current.
infact we consider infinit value for input impedance of it and therefor zero input current. it is very simple to understand , if we consider infinit value for input impedance so we could have infinit gain in output current value:!:

by the way , you can find any concept about analog modulation in every communication system book, such as the book by proakis and salehi.
by.
 

Re: open loop op amp

For example, Corrected Closed Loop Gain: Av = Acl / (1 + Acl/Aol), where if Aol >> Acl then Av = Acl
cl=closed loop
ol=open loop
Regards,
IanP
 

open loop op amp

Just ideal operational amplifiers have infinite gain but in the real world they have large finite gain and you may control it using negative feedback.
 

Re: open loop op amp

We electronic engineers assume that the gain is infinite in open loop because this is a theoretical model and you want from an amplifier infinite gain; you want to apply a signal to the amp and you want to get a signal from the amplifier that is infinite big...
 

open loop op amp

hi!

read the second chapter on op-amp basics by sedra and smith. you will get the answer for your question.

regards,
vijay
 

Re: open loop op amp

as you can see the the gain using feedback by reading and solving it's equation
now just think that the feedback resistor is open circuited (i.e.∞ resistance) and now apply in the gain formula
real life gain is very low
 

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