General Impedance Converter.

Cuthbert Nyack
Laddder filters can require large inductors if designed for low frequencies. These inductors are not only inconvenient, their resistance can also have an adverse effect on the frequency response of the filter. The circuit of a general impedance converter is shown above along with the value of the impedance seen looking into the Vin terminal.
To simulate an inductor, impedance Z4 is a capacitor and the other impedances are resistors, the impedance of the circuit is
Z = (sCR1R3R5/R2)
This is equivalent to an inductor L = (CR1R3R5/R2)
This configuration is used to simulate large grounded inductors in ladder networks.
To simulate a FDNR or D element Z1 and Z3 are capacitors while the other impedances are resistors. The impedance is
Z = R5/(s2C2R2R4)
with D = (C2R2R4)/R5
If a ladder network has grounded capacitors then the components can be multiplied by 1/s, resistors become capacitors, inductors become resistors and capacitors become D elements. The resulting grounded D elements can then be simulated by the GIC.
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COPYRIGHT © 1996 Cuthbert A. Nyack.