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what do you mean by first order, second order and third order filters?

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devil6600

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hi
can any one tell me what is the meaning of first order, second order and third order filter?
if i consider a simple low pass filter (only capacitor) then what will be its order?
thanks
 

Order of filter is defined by number of active elements in the filter. So a capacitance filter is the first order filter and is 6dB/ octave. If you add a inductor you have a second order filter (i.e two active elements) and you get 12dB/ octave. Similarly a forth order filter have four active elements and 24dB/Octave.
Order of filters
Octave (electronics) - Wikipedia, the free encyclopedia
 

if you use only a capacitor then it acts as a cutoff frequency after that the response drops
first order low pass has 1 resistor and a capacitor in parallel to ground which is also called as 1pole filter
second order filter has 1pole as above and second as resistor in series and capacitor for gain
active filters are of mainly three types buttorworth , chebeshev and bessel filters , butterworth is more commonly used filter
 

Order of filter is defined by number of active elements in the filter.
Click to expand...
1. I guess, you mean reactive elements
2. It's not generally, true, only for some of the simple filter prototypes you mentioned. A 3rd order Chebyshev II or elliptic low-pass has more reactive elements.

Strictly spoken, filter order refers to the order of the denominator polynominal in the transfer function, the highest power of s occuring in it.
 
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