Power supply filtering: When a C becomes RLC and an L becomes an RLC
Hello,
I have a circuit with one digital and one analog 7805 regulator. I am
having trouble filtering out the EMI caused 64MHz 5V oscillator in the
digital circuit from entering the 7805 regulator on the analog
circuit. I built some filters using second order LC, pi C-R-C
circuits, pi C-L-C with limited success. I tested them all on a plain
pre-drilled board where I soldered the components in a neat fashion
and checked using 5V oscillator modules with a 100MHz oscilloscope and
10X probes . All of them attenuated well 5V square waves up to a few
MHz, but when I put a 64MHz signal at the input, it just went straight
though. It is as if all the capacitors have parasitic inductances that
make the components act like inductors and the inductors acted like
L-C resonators... Could somebody recommend a topology for my filters ,
type of dielectric, type of inductor etc...
Frank
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