Order of LC low pass filter

[iamakda]

Hello,

I have a question that I have a LC low pas filter with 1 inductor in series with the supply and 1 capacitor in parallel of output. So this is the 2nd order filter.
But if I connect another filter of same configuration ahead of 1st LC filter then would it be the 4th order filter? See the attached circuit to get the more clear picture.

[momaka]

Re: Order of LC low pass filter

I'm not entirely sure what order it will be. You will have to look at the transfer function (Vo/Vi) you get for that circuit.
*EDIT*
You can find the transfer function by solving with impedance.
Impedance of a capacitor: 1/Cs
Impedance of an inductor: Ls
Impedance of a resistor: R
Once you convert the circuit parameters for each component in the proper impedance, you solve the circuit with Ohm's law as if the components were resistors (where the resistance is replaced by the impedance of that component).
Finally you write the transfer function and look at the denominator - more particularly the power of "s". This is the order of the system.

[iamakda]

Re: Order of LC low pass filter

I'm not entirely sure what order it will be. You will have to look at the transfer function (Vo/Vi) you get for that circuit.
*EDIT*
You can find the transfer function by solving with impedance.
Impedance of a capacitor: 1/Cs
Impedance of an inductor: Ls
Impedance of a resistor: R
Once you convert the circuit parameters for each component in the proper impedance, you solve the circuit with Ohm's law as if the components were resistors (where the resistance is replaced by the impedance of that component).
Finally you write the transfer function and look at the denominator - more particularly the power of "s". This is the order of the system.

Thanks Momaka,

But could you please do it for me and attach it as a picture as I really do not know how to do it....Please.....

Thanks once again.

[budm]

Re: Order of LC low pass filter

http://www.corollarytheorems.com/Design/filter.htm

[Longbow]

Re: Order of LC low pass filter

The order of a filter is simply the number of reactive elements in the circuit, in your case 4 reactive elements (L or C) gives you a 4th order filter. The response of the filter cannot be completely predicted without knowing the Q of each element, and the source and load impedances.

[budm]

Re: Order of LC low pass filter

http://mysite.du.edu/~etuttle/electron/elect31.htm

[momaka]

Re: Order of LC low pass filter

Thanks Momaka,
But could you please do it for me and attach it as a picture as I really do not know how to do it....Please.....
Thanks once again.

Sorry for the late reply. I tried to do it last week but it's been a year since I've used this stuff so my knowledge is very rusty. Will definitely need to review some material to give you an answer. Let me know if you still need it.

[iamakda]

Re: Order of LC low pass filter

Sorry for the late reply. I tried to do it last week but it's been a year since I've used this stuff so my knowledge is very rusty. Will definitely need to review some material to give you an answer. Let me know if you still need it.

Hi Momaka,

Yes, I still need it mate....

Thanks and awaiting for your reply.

Regards.

[momaka]

Re: Order of LC low pass filter

Reviewed, but still can't seem to get it right. I keep getting nonsense for the answer.
... And to think that I used to know this stuff perfectly. I should really quit school, lol .