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design very low active low pass filter

john.agcos

Dec 12, 2013
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i am suffering to design very low frequency like 0.0001hz to 50KHz filter for very low signal.
i want to design this preamplifier circuit. i have design but it can not amplify lower frequency signal.
 

davenn

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Sep 5, 2009
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Hi John
welcome to the forums :)

0.0001 is extremely low!!
the ones I use for seismic recording go down to ~ 0.005
Im mainly interested in seismic waves of ~ 10 to 100 seconds

what are you recording/measuring that has a period down to ~ 10,000 seconds ??

Dave
 
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john.agcos

Dec 12, 2013
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thanks a lot davenn
i am designing this preamplifier circuit.
and i am fine if i design for 0.001Hz to 50KHz.

can u give me that circuit which is you use for 0.005
 
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davenn

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I will see if the guy will release a copy of the circuit
He likes to keep the info reasonably secure ;)

Just curious, cuz of my geophysics background.....
when you say, geophysical sensor, what sort of sensor ?

I know in years gone bye that both Australian and Greek geophysics guys have done research into large earth currents

a geophone or other seismometer ? or an EM emission from the earth ?

for your interest here's a link to my online seismograms

cheers
Dave
 
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davenn

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here's a freq response for his preamp
it may be a bit narrow for your needs ?

attachment.php



all you really need is a preamp ( LOW NOISE) that has a 50kHz LPF cutoff
doing some google searching on 50kHz LPF may well give you some options
as the above plot is showing that the preamp front end is being band passed rather than just low passed

cheers
Dave
 

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john.agcos

Dec 12, 2013
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thanks davenn

is that sallenkey active amplifier works at very low frequency?
 

john.agcos

Dec 12, 2013
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hi daven
can you tell me which kind of amplifier is use for that preamplifier0.005 to 50KHz.

and can you tell me how to reduce flicker noise?
 
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