Test filter response on Schematics

[dammadmin]

Hello all. I have worked out a 1st order low pass Butterworth filter for a load of 5 Ohms and cut-off frequency of 60 Hz and I have used the First Cauer form to implement the LC filter. I have calculated values of input inductance (L1), shunt capacitance(C1) and output inductance(L2). I want to obtain the frequency response of the filter on Schematics. I want to know where the actual cutoff frequency is.

Any ideas how I can simulate and find this response?? I will be using this filter with another circuit later..

:|:?::?:

 

[keith1200rs]

Just simulate it with any Spice simulator. Most free demo versions will do that or LTspice.

Keith.

 

[LvW]

Hello all. I have worked out a 1st order low pass Butterworth filter for a load of 5 Ohms and cut-off frequency of 60 Hz and I have used the First Cauer form to implement the LC filter. I have calculated values of input inductance (L1), shunt capacitance(C1) and output inductance(L2). I want to obtain the frequency response of the filter on Schematics. I want to know where the actual cutoff frequency is.

Any ideas how I can simulate and find this response?? I will be using this filter with another circuit later..
:|:?::?:

My recommendation for you is to become familiar with the topics filter theory.
A first order filter canot have a Butterworth response. More than that, an LC filter has a minimum order of two! Later you speak of L1 and C1 and L2, which corresponds to an order of three! Compare this with your first sentence (1st order).

 

[abbeyromy]

To help you further with SPICE simulation. I am attaching an example showing step by step approach to simulate a low pass filter. Once you understand the steps you can simulate any filter.

Hope it helps
-Hemanshu

 

[dammadmin]

Thanks Hemanshu..

@LvW.. sorry i wrongly put the order..its a 2nd order filter.. I have managed to work it out thanks again..

 

[LvW]

To help you further with SPICE simulation. I am attaching an example showing step by step approach to simulate a low pass filter. Once you understand the steps you can simulate any filter.
Hope it helps
-Hemanshu

Just two comments to the presented step-by-step approach:
* Point 1: 10001 points/dec is not necessary (too time consuming); 100 points/dec are sufficient
* Point 4: The 3-dB-point is not for all second (or higher) order filters identical to the characteristic bandwidth. See the bandwidth definition for (elliptical) Cauer and Chebyshev responses.