Can somebody tell me what the f is in the magnitude formula? I know Ho is the dc gain, fB is the 3db cut off frequency and n is the order.

 

nobody know what f is then?

 

Hello,

Can you show the formulas?
The f will most probably be the frequency.
and fB the border frequency of the filter (-3dB point).

Bertus

 

The attached is the formula and the question is:

Analyse the magnitude and phase characteristics of a 2nd order butterworth lowpass filter

not sure how to go about this.

Also forgot to mention that the cutoff frequency is 1000hz

 

Hello,

The H0 is the passband gain.
When f = fB the gain will be
H0/sqr(1+(f/fB)^2n) =
H0/srq(1+1^2n) =
H0/sqr(2)=
H0/0.707 ,
wich is - 3dB.

Bertus

 

doesnt this mean all orders will give the same result? How would magnitude and phase be analysed then?

 

Hello,

Take a look at the PDF in this link:
http://cnx.org/content/m34921/1.1/?format=pdf

Bertus

 

looking at the graph on page 5 shows n= 1,4 and 10 and gives different results. so how does this apply to the formula when the magnitude is always 1/root2

 

Hello,

You mean this graph:

All the lines go through the same point at f/fB =1.
This is the -3 dB point.

Bertus

 

so magnitude for all orders is the same? just the question says analyse magnitudes of 2nd and 4th order.

 

Hello,

The magnitude is only the same for all at the - 3dB point.
Before and afther that point the values are diffetent as you can see in the graph.

Bertus

 

so what is this formula used for? Can you explain what the magnitude and phase is for 2nd order as an example so I can try other orders