Good afternoon all,
I'm currently working on a Pie - low pass - filter, and I can't seem to figure out few bits about it.

1) In the past when I've done the low pass filter 1rd order, the power loss was -3dB at fc; however I'm not sure what it supposed to be as this circuit is 3rd order ? (My circuit starts from + 20dB and not 0 dB ??)

2) fc = 1/2*pie*sqrt(LC) ---> fc = 15Khz
I tried calculating the value for the capacitor, however they are in parallel ?
c = 1/(900*10^6)*(pie^2)*L

If I follow my formula, do I still have to divide the capacitance by 2 ?

I have attached simulation of two build circuits, the one with the load resistance is the one I would like to use for the project.

I look forward to hear from someone, with adequate knowledge.

Best

 

It is not clear to me how you start your design.
The "normal" (classical) procedure is first to formulate the requirements to the filter transfer function:
* order of the transfer function (damping requirements)
* Approximation (Butterworth, Chebyshev, Bessel...)
* Gain and damping requirements (passband edge, corner frequency,)

 

Hi LvW,
The only requirements are for the filter to have fc - 15Khz and It needs to be a Pie Filter.
I'm not sure how to handle this, hence why I'm asking.

 

A nit, but it's "Pi" (filter schematic looks like the Greek letter π) not Pie.

 

A nit, but it's "Pi" (filter schematic looks like the Greek letter π) not Pie.

Yes, it's Pi filter

 

Hi LvW,
The only requirements are for the filter to have fc - 15Khz and It needs to be a Pie Filter.
I'm not sure how to handle this, hence why I'm asking.

Hi LvW,
The only requirements are for the filter to have fc - 15Khz and It needs to be a Pie Filter.
I'm not sure how to handle this, hence why I'm asking.

What about the resistor values (R1, R2)? Are you free to select other values?

 

What about the resistor values (R1, R2)? Are you free to select other values?

No, I'm afraid.

The Rs = 50 is essentially the function generator & the RL = 1MEG is the oscilloscope.

I have to use those two.