Filter Identification

Thread Starter


Joined Nov 14, 2007
Is there any way to determine what type of filter you have without deriving the transfer function from a provided RCL circuit sketch? As an example i am dealing with a homework problem that gives three circuit filters and wants me to identify what type they are. I know how to get the transfer function for them and then roughly sketch a Bode plot but i feel that there must be an easier way to do this. Maybe by looking at each circuit element and whether they are in series or parallel with one another....


Joined Apr 20, 2004
Think about the response of a capacitor and then an inductor to frequency. Look at the arrangement of the C and L elements in the various circuits in that light, and see what it suggests to you.


Joined Sep 18, 2007
Just to play off what beenthere said, think about what happens at low frequencies and also what happens at extremely high frequencies and that will, along with the placement of components, what type of filter you are looking at.


Joined Dec 25, 2006
Yes, and infact many engineers do this. There are three types:

1) Purely theoretical. 'Show me the math' type of guys. They will astound you with their ability to solve TF's in their head. Then will will explain the circuit to you.

2) Purley practical. Cannot or will not explain a circuit using equations. They will think of how elements respond to voltage, current, frequency, etc. A more 'inuitive' or conceptual feel for the circuit.

3) A little bit of both. I am like this.