Saturday, 9 March 2019

Sallen Key topology input and output impedance


schematic


Ideal Operational amplifier


Zi=(R1+R2)||Zc2


Zo=0


741 Operational amplifier


Zi=(R1+R2)||Zc2



Zo=0 (at DC)


For the input impedance when using a 741 I am not sure if I should consider the Fairchild version of the 741 graph showing input resistance vs frequency impedance (at DC is about 6Mohm) so It would be Zi=((Zc2||R_OA)+R2))||Zc1+R1




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