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A pie filter design - 3 pole with an added capacitor to Gnd.

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qq8807

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Hi everybody.

Need a brilliant opinion from all of you.

I would like to design a 3 elements low past filter that is cut off at 1MHz and the required attenuation is at 2MHz. The impedance of the equipment is 50ohm. Meaning, I will use this filter with the 50ohms system.

If I design by 3 elements (2 caps (C1,C2) and an inductor (L1) - pie low pass filter), I will get the cap value of C1=C2=3.2nF while the L1=15.9uH.

What will happen if I add another capacitor (C3) parallel with the C2?

Is the 50ohms impedance of C2 wil have to be divided with C3. Because, the cap in parallel, its capacitance need to be added. I am confuse here.

Please kindly help me with your advices. :confused:

rgds,
QQ.
 
Hi everybody.

Need a brilliant opinion from all of you.

I would like to design a 3 elements low past filter that is cut off at 1MHz and the required attenuation is at 2MHz. The impedance of the equipment is 50ohm. Meaning, I will use this filter with the 50ohms system.

If I design by 3 elements (2 caps (C1,C2) and an inductor (L1) - pie low pass filter), I will get the cap value of C1=C2=3.2nF while the L1=15.9uH.

What will happen if I add another capacitor (C3) parallel with the C2?

Is the 50ohms impedance of C2 wil have to be divided with C3. Because, the cap in parallel, its capacitance need to be added. I am confuse here.

Please kindly help me with your advices. :confused:

rgds,
QQ.

How much attenuation do you need at 2MHz? a 3 pole design will only give you about 18 dB attenuation at 2MHz.
If I recall, the rule of thumb is 6dB per pole per octave.
 
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