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Help me with designing a low pass filter

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Anachip

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Low Pass Filter Design

Hi People,

Im desigining a feedback system. Im extracting a dc point from the output of differential amplifier through a low pass filter. Now my problem is, i want to have a low cutoff frequency of 50kHz. But from the LPF response, my low cutoff freq is 5kHz which is very low. What I know is, we can tune the desired value by the R & C component with the formule f=1/2*pi*R*C. But im not achieving the desired value although i vary them. Please guide me on how do i get them.

Thanks,
Anachip
 

pop48m

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Re: Low Pass Filter Design

Anachip said:
But from the LPF response, my low cutoff freq is 5kHz which is very low. What I know is, we can tune the desired value by the R & C component with the formule f=1/2*pi*R*C. But im not achieving the desired value although i vary them.

You have probably made a mistake in the values of capacitor or resistor, since you get 10 times lower result.
How do you measure your LPF response?

Pop
 

narccizzo

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Re: Low Pass Filter Design

as anachip says maybe you have a mistake with the values
this filter gives a cut fracuency of 50KHz, for first order filters the cut frecuency its given by vout = vin / √2
if vin = 1V, when vout = 1 / 1.4142 = 0.707 you are in the cut frecuency.
this is the simulation for a C proposed of 10nF and R calculated with the ecuation that you put above.
hope this helps..
 

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