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# Discussion Groups | Comp.DSP | butterworth high pass fourth order design

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# butterworth high pass fourth order design - sid4u - 2006-03-15 19:41:00

```hi,

can anybody help me to design and implement an fourth order butterworth
high pass filter in s domain.here are the specs

input = 1kHz sine
order = 4
fs = 20kHz
As = 80dB

sid```

# Re: butterworth high pass fourth order design - Jerry Avins - 2006-03-15 23:03:00

```sid4u wrote:
> hi,
>
>    can anybody help me to design and implement an fourth order butterworth
> high pass filter in s domain.here are the specs
>
> input = 1kHz sine
> order = 4
> fs = 20kHz
> As = 80dB
>

If you don't know how to design it, how do you know it's what you need?
The frequency into a filter is not usually one of its specifications.
I'm pretty sure that As, whatever that means, is not independent of the
order, and so can't be independently specified.

In the s plane, the poles of a Butterworth filter are uniformly
distributed around a circle.

Try http://www.maxim-ic.com/appnotes.cfm/appnote_number/1795.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯```

# Re: butterworth high pass fourth order design - HelpmaBoab - 2006-03-16 21:54:00

```"sid4u" <v...@gmail.com> wrote in message
news:u...@giganews.com...
> hi,
>
>    can anybody help me to design and implement an fourth order butterworth
> high pass filter in s domain.here are the specs
>
> input = 1kHz sine
> order = 4
> fs = 20kHz
> As = 80dB
>
> sid
>
>

You fitst need to deisgn the low-pass prototype. You then need to transform
low pass to high pass.
What ripple do you need in the passband? If it is 3dB you can look up in
tables what the Butterworth polynomial is.

Tam```

# Re: butterworth high pass fourth order design - John E. Hadstate - 2006-03-18 19:08:00

```"HelpmaBoab" <F...@yahoo.co.zpc> wrote in message
news:2ypSf.6728\$J...@news.xtra.co.nz...
>
> "sid4u" <v...@gmail.com> wrote in message
> news:u...@giganews.com...
>> hi,
>>
>>    can anybody help me to design and implement an fourth
>> order butterworth
>> high pass filter in s domain.here are the specs
>>
>> input = 1kHz sine
>> order = 4
>> fs = 20kHz
>> As = 80dB
>>
>> sid

To the OP: Google is your friend.  Some time ago I was
researching a similar problem.  Google led me to a site with
a Java applet that will calculate the coefficients for
several types of IIR filters given the specifications you
cited.

>>
>>
>
> You fitst need to deisgn the low-pass prototype. You then
> need to transform
> low pass to high pass.
> What ripple do you need in the passband? If it is 3dB you
> can look up in
> tables what the Butterworth polynomial is.
>
>
> Tam
>

Butterworth has no ripple in either the passband or the
stopband.  It is "maximally flat".
>```

# Re: butterworth high pass fourth order design - sid4u - 2006-03-21 15:10:00

```thanks for ur responses.

>"HelpmaBoab" <F...@yahoo.co.zpc> wrote in message
>news:2ypSf.6728\$J...@news.xtra.co.nz...
>>
>> "sid4u" <v...@gmail.com> wrote in message
>> news:u...@giganews.com...
>>> hi,
>>>
>>>    can anybody help me to design and implement an fourth
>>> order butterworth
>>> high pass filter in s domain.here are the specs
>>>
>>> input = 1kHz sine
>>> order = 4
>>> fs = 20kHz
>>> As = 80dB
>>>
>>> sid
>
>To the OP: Google is your friend.  Some time ago I was
>researching a similar problem.  Google led me to a site with
>a Java applet that will calculate the coefficients for
>several types of IIR filters given the specifications you
>cited.
>
>
>>>
>>>
>>
>> You fitst need to deisgn the low-pass prototype. You then
>> need to transform
>> low pass to high pass.
>> What ripple do you need in the passband? If it is 3dB you
>> can look up in
>> tables what the Butterworth polynomial is.
>>
>>
>> Tam
>>
>
>Butterworth has no ripple in either the passband or the
>stopband.  It is "maximally flat".
>>
>
>
>```