i have a small problem with amplifier !

Thread Starter

tallo

Joined Mar 4, 2011
12
hi engineers ..

i have a small problem with the following question




how can i determine the input impedance for the two types of amplifiers

thank you
 

Thread Starter

tallo

Joined Mar 4, 2011
12
Zin(I) = Ri

Zout(I) Almost equal to 0

:::::::::

Zin(NI = (1+Aol B ) Zin

Zout(NI) = Zout/(1+Aol B)

where B + Ri/(Ri+Rf)
 

Ron H

Joined Apr 14, 2005
7,063
Zin(I) = Ri

Zout(I) Almost equal to 0

:::::::::

Zin(NI = (1+Aol B ) Zin

Zout(NI) = Zout/(1+Aol B)

where B + Ri/(Ri+Rf)
With ideal op amps, your equations will give you the answers. That is, if you know the values of Ri and Aol for an ideal op amp.
 

Ron H

Joined Apr 14, 2005
7,063
i am very confusing

if these amps are ideal , what will be the solution
Your equations are very simple.

and, if they are in practical model

what the solution will be ?
Many op amps don't specify input resistance, but they all specify voltage gain.
This is homework. We don't do homework for you. Work on it until you get stuck, show us your results and how you got them, and we will try to help.
 

Audioguru

Joined Dec 20, 2007
11,248
You cannot calculate the gain of the inverting opamp unless you know the input impedance of the source which is in series with the input resistor.
Can you assume it is zero ohms?
 

Ron H

Joined Apr 14, 2005
7,063
You cannot calculate the gain of the inverting opamp unless you know the input impedance of the source which is in series with the input resistor.
Can you assume it is zero ohms?
OMG! He's confused enough already. You've just opened a whole new can of worms.:D
 

Audioguru

Joined Dec 20, 2007
11,248
An inverting opamp is a can of worms because its gain is determined by the input resistor value in series with the source impedance.

Make a non-inverting opamp circuit with a very high input impedance instead.
 
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