3rd order HIgh pass filter - explanation?

[APaddy]

hi guys

can anyone give a detailed description of what a 3rd order high pass filter is???

what is the 3rd order part ???

and also how to calculate the cut of frequency???

thanks guys

 

[richie00boy]

A high-pass filter lets the highs pass and attenuates the lows.

The filter order represents the number of poles in the system. Basically the higher the order the steeper the cut-off slope.

I don't have the formulas to hand, but you should be able to find them in books such as Don Lancaster's Active Filter Cookbook (assuming an active filter).

 

[APaddy]

thanks richie00boy for clearing up the 3rd order explanation!!



does anyone know a good website for this stuff...?


need this info for my project report!!!

thanks

 

[AndrewT]

Hi,
I think ESP has a couple of sections on active filter cutoffs and poles(slope), maybe also passive?
http://sound.westhost.com

For passive try Nelson Pass at http://www.passdiy.com

 

[APaddy]

thanks andrew

will check em out!!!

 

[Ouroboros]

Download 'Filterlab' from the Microchip website. A wonderful little program for filters up to 7th order.

 

[phase_accurate]

The filter order represents the number of poles in the system. Basically the higher the order the steeper the cut-off slope.

Another way of expressing this is: The order is the same as the amount of components that show a frequency-dependant behaviour (i.e. inductors and/or capacitors) in a filter.

Regards

Charles

 

[MosfetOwner]

what is the 3rd order part ???

The other people have already answered most of your questions. However, the 3rd order part means that below the cutoff frequency, the level will roll off at 18dB per octave. A first order filter rolls off at 6dB/octave, a second order at 12dB/octave and so on. An octave is a halving (or doubling) in frequency.

 

[APaddy]

thanks guys

does anyone have on hand the calculations used to caclulate the cut off and 3 rd order part.

thanks

 

[Cal Weldon]

Are you looking for a passive filter calculator?

If so, here's one: http://www.mhsoft.nl/spk_calc.asp

 

[APaddy]

ahhh thanks

but i need the manual calculations to work out how i got a 1khz cut off frequency and how i got 18db per octave and a 3rd order from a high pass filter

help anyone???

 

[richie00boy]

What level of study are you at? If you want the calculations for why it's 3rd-order you are looking at A-Level+ maths calculus.

However, if you just want formula for calculating cut-off frequency and Q then it's a lot easier. Have you got a library you can go to and see if they have The Active Filter Cookbook by Don Lancaster?

 

[phase_accurate]

This one will give you the schematic diagram and the values. The proposed circuit is inverting however.

http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/filter/filter.html

Regards

Charles