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filter design
Moderators: Ajay Bhargav, Arun Kumar V, pdi33, Shailesh NAYAK, ۞ TPS ۞, shyam, sashijoseph, ExperimenterUK, DavesGarage
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priya123
Wed Jun 18 2008, 05:40AM
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sir,
Iam very new to the concept of filter designing.I want to design a high pass filter (butterworth) with op-amp .I need a cut-off frequency of .03hz.how should I proceed?

p
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sashijoseph
Wed Jun 18 2008, 02:23PM

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The simplest configuration for a Butterworth alignment is a Sallen-Key arrangement.Do you want a single pole(6dB/octave) or double pole(12dB/octave) filter?
A double pole SallenKey would look like this :


For a butterworth alignment C1=C2 and R2=2xR1.
The corner frequency is determined by R1 and C1.
For calculating component values first settle on the capacitor value...say 47uF.
Then
R1=0.707/(2*pi*F*C1)
In your case
R1 = 0.707/(2 * 3.14 * 0.03 * 0.000047)
R1=80K
Thus R2=160K
C1=C2=47uF

Let there be music........
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pdi33
Wed Jun 18 2008, 10:24PM

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thanks shashi, very useful info. Hope Priya got the answer :-)
* inspired to develop,developing to inspire *
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priya123
Thu Jun 19 2008, 06:11AM
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thanx a lot shashi sir,i just want to know if I choose a single pole filterhow will the circuit look like?
sir also provide me the values of capacitors resistors for the respective circuit

[ Edited Thu Jun 19 2008, 06:15AM ]
p
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Arun Kumar V
Thu Jun 19 2008, 07:38AM

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hello priya123,

can we know where you are using this filter- i mean which circuit/application


Arun
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sashijoseph
Thu Jun 19 2008, 01:04PM

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priya123 wrote ...

thanx a lot shashi sir,i just want to know if I choose a single pole filterhow will the circuit look like?
sir also provide me the values of capacitors resistors for the respective circuit

A single pole filter will have only a single capacitor-resistor pair. Like this ..



The formula is..
F = 1/(2*pi*R*C)

For F = 0.03Hz and C = 57uF(47uF and 10uF in parallel),R will come to ~93K.

Why have you chosen such a low cutoff? Some medical equipment?
Let there be music........
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priya123
Fri Jun 20 2008, 12:51AM
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hello sir,
u are absolutely right ,actually I am trying to design a medical ECG monitoring circuit using instrumentation amplifier ad620a,some filter with a low cut-off,just one more query sir,please tell me how to design a protection/isolation circuit to prevent current leakage.
thanking u.
p
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pravin_35
Sun Aug 09 2009, 11:18PM

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hi,

for medical application u want to know more abt the signal processing, first wat is the range of frequency you going to monitor.. for u r using protection circuits (isolation)


pravin





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