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I would like to know if that is correct schematic1

Ideal Operational amplifier

Zi=inf

Zo=Zc||R

741 Operational amplifier

Zi=2Mohm+R+Zc

Zo=Zc||(R+75ohm) (at DC)

schematic2

Ideal Operational amplifier

Zi=R+Zc

Zo=0

741 Operational amplifier

Zi=R+Zc

Zo=75ohm+(R||Zc) (at DC)

I have used plot of output resistance from LM741 dataseet

Thanks in advance.

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Because you are using the op-amp in a closed loop configuration, any output impedance at DC is virtually zero (see my previous answer). So, for the first circuit, when using the 741 op-amp the output impedance Zo=Zc||R.

For the input impedance, the wrong answer is Zi=2Mohm+R+Zc because the op-amp buffers the output resistor and capacitor from having any influence at the input and Zin is what the data sheet says about the 741 (typically 2 Mohm).

For your 2nd circuit, the output impedance is virtually zero ohms at DC for the reasons given in my previous answer. As frequency rises the output impedance rises.

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  • \$\begingroup\$ Hi Andy I promise this is the last question, thanks in advance! electronics.stackexchange.com/questions/321860/… \$\endgroup\$ – Fran Aug 2 '17 at 12:27
  • \$\begingroup\$ That is a subtley much more difficult question to answer because of the feedback capacitor. unfortunately I'll be on a tiny and puny android for the next three days so I can't do it justice. \$\endgroup\$ – Andy aka Aug 2 '17 at 12:53

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