The Attempt at a Solution
Hi all, i have some doubts on how to find the impedances for active filter circuits.
Let's start with a simple low pass filter :
The input impedance should be R + Xc; and the output impedance should be ZL || (RF+R1) once i short the input.
However, a same filter but at 2nd order configuration is confusing me. Assuming the circuit diagram is given as below :
Will be output impedance be solely ZL || (RF+R1) if seen from port A-B ? Or will it have to include the feedback capacitor and the input side with the source short-circuited as well?
As for the input impedance, is this derivation method along the right line?
applying KCL at red node V1
Ii = I1 + I2
(Vi-V1)/R1 = (V1-Vo)/XC2 + (V1-0)/(R2+XC2)
where vo=KVx ; K is the DC voltage gain of the amplifier.
Vx = (V1*XC1)/(R2+XC1)
After that, from definition of Zi = Vi/Ii; try to arrange the equation to fit Vi/Ii?
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