Help me with designing a low pass filter

[Anachip]

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]

Re: Low Pass Filter Design

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]

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..