Bandwidth of this LC filter

[EDA_hg81]

Please let me know how to calculate the bandwidth of this LC filter?

Thanks.

 

[FvM]

Without specifying a source and load impedance and possibly inductor Q, you can't calculate a bandwidth.

 

[karesz]

Hi EDA_hg81,
Or you means the cut-off frequency?
K.

 

[LvW]

Hi EDA_hg81,
Or you means the cut-off frequency?
K.

Ohh - is there a difference between bandwidth and "cut-off"?

 

[karesz]

Badwidth is for me only for bandfilters/rejectors & these is a TP-oder?
Here is Q no matter. Sind wir bitte einig?

K.

 

[LvW]

Badwidth is for me only for bandfilters/rejectors & these is a TP-oder?
Here is Q no matter. Sind wir bitte einig?

K.

No, sorry. For my understanding - and this is in agreement with most of all relevant textbooks - a low pass has a usable bandwidth which equals the cut-off frequency.
Concerning Q: The cut-off frequency as well as the filter shape (low pass approximation) depend, of course, on the inductor Q (and the source impedance).

 

[FvM]

The circuit doesn't clearly show a low pass, but I understand now, that it's meant as such. Cut-off is 1/(2pi√LC).

 

[EDA_hg81]

Thank you all.

I am wondering it is Low pass filter?

Why he used two caps?

 

[karesz]

Yea LvW,
Clear; you are correct with shape factor vs Q, but how plays it pls to cut-off frequency?
K.

 

[EDA_hg81]

My question is :

The serial data are sent out to a bluetooth module for being transfered out.

Should this data line be connected with a lowpass filter in series?

The drawing at the first post shows the power filtering.

Thanks

 

[karesz]

Hi & Tnx!!
Maybe you can up load more of your ciruit pls, not only a smal portion?
K.

 

[EDA_hg81]

This is the only I have.

The rest of schematic only show the Module interfaces.

 

[LvW]

Yea LvW,
Clear; you are correct with shape factor vs Q, but how plays it pls to cut-off frequency?
K.

It is really simple to calculate the transfer function and to verify that each part determins the frequency behaviour and the cut-off frequency - even a parasitic resistance of the lossy inductor.

 

[kokabanga]

Transfer Function from 3.3V point to output across parallel capacitor at Test Point (TP21) is

1/(1+S^2 LC)

where

C = C26 + C27

L = 1uH

 

[LvW]

Hi kokabanga,

perhaps you have overlooked that - from the start of this topic - the possible influence of a finite inductor Q (loss resistance) has been discussed.

 

[karesz]

Hi,
Sorry, but is all these with Q in them case not only an "academical" aspect pls?
K.