I *meant* to answer at the time! Dennis Plunkett wrote: > I have to design some filters for my course (Low pass), and some of > them are balanced, and are to be considered way above ground (Some are > not). If I am to design this filter, do I do it as a normal > unbalanced type and then put the same inductance in the other leg and > 1/2 the shunt capacitance? > Filter unbalanced 1MHz 15µH 15µH 1200pF 4700pf 1200pF GND GND GND OK, if you want this balanced at the *same* impedance, you have to re-distribute the inductances symmetrically. This is performed by taking half of each inductance and putting it in the other side: 7.5µH 7.5µH 1200pF 4700pf 1200pF 7.5µH 7.5µH If in addition you want to "center-tap" the capacitances, each must be substituted by two in series of double the capacity: 7.5µH 7.5µH 2400pF 9400pf 2400pF GND GND GND 2400pF 9400pf 2400pF 7.5µH 7.5µH If you wanted to do much the same thing, but wanted twice the characteristic impedance, you would just mirror the original circuit: 15µH 15µH 1200pF 4700pf 1200pF GND GND GND 1200pF 4700pf 1200pF 15µH 15µH For four times the impedance (as if fed by a 2:1 balun), you follow the same "rule" and double inductances, halve capacitances: 30µH 30µH 600pF 2350pf 600pF GND GND GND 600pF 2350pf 600pF 30µH 30µH And again, if you didn't want the earth reference: 30µH 30µH 300pF 1175pf 300pF 30µH 30µH I think that's how it works... -- Cheers, Paul B.