Hi,

Can anyone tell me where could i find the desciption/circuit diagram for this filter. Actually i know nothing about the bessel filter.

 

What specifically do you want to know about this particular filter topoplogy?

Are you interested in the active or passive version of such a filter?

hgmjr

 

Actually i want to know how to design this filter. For example i want to design a 6 pole high pass bessel filter with cutoff frequency 1kHZ. Where should i start it?
How the number of pole affect the design? What i know is only about low pass and high pass RC filters.

 

Here is the wikipedia article. Follow the hyperlinks for more information
http://en.wikipedia.org/wiki/Bessel_filter
Here is a set of design tables
http://www.rfcafe.com/references/electrical/bessel_proto_values.htm

 

You can use op-amps for a 6 pole filter. In my experience, I have only seen 2 pole stages cascaded together to form higher order filters.

 

If you think about it for a minute you realize that any active high-pass filter is actually a band-pass filter. The upper limit is controlled by the opamp characteristics. In both active and passive filters you get to six poles by cascading stages. The number of poles controls the slope of the rolloff between the stopband and the passband.

 

You can use op-amps for a 6 pole filter. In my experience, I have only seen 2 pole stages cascaded together to form higher order filters.

I am partial to breaking a filter with 6 poles up into section as knightofsolamnus has recommended mainly as it makes it somewhat easier to analyze. There are sources of tables that provide the normalized filter coefficients for filter implemented in this way.

hgmjr

 

The Analog Devices Website has a very good Filter Tutorial that has the tables that I made reference to earlier.

You may already know this but the tables such as the ones in this tutorial are aimed at filter designs with 1 rad/sec as the -3dB corner frequency. Once you have chosen the topology of filter (Bessel, Butterworth, etc) you can then use the tables to provide a starting point for your filter. You will then use frequency scaling and impedance scaling to translate from the 1 rad/sec case to your frequency and real world component values.

hgmjr

 

From the filterlab, i designed the 6 pole low pass bessel filter (figure) because the high pass bessel filter can't be designed in filterlab. What modification that i should make to the circuit to make it as a high pass filter. Should i change the position/value of resistor/capasitor or the circuit of low pass filter is totally different to the high pass filter.