[SOLVED] second order filter design

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ashugtiwari

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second order filter

Hi All,
The circuit shown is 2nd order filter with laplace transform of:
Vout(s)/Vin(s) = 1/(L*C*s^2+1)
The resonance occurs at 3.558812717kHz if L=200uH and C=10uF.
How to determine the magnitude and phase freq response from the given transform and how to use matlab to find this? Are these above values of L and C should be used to make it low pass filter with 3.5kHz or what values should be used.
Thanks in advance.

Ashutosh
 

2nd order filter

To get a 2nd order filter, the bandwidth is 1/(2*pi*sqart(L*C)).So L=200uH and C=10uF is OK.
however,to avoid overshooting,you should add a resistor followed.And Q value should better be less than 1.
Q= sqart(L/C)/R.
May it be helpful for you!
 
Thanks mangcy,

Well What actually this Q is and its characteristics, how it will alter the freq response of filter. I had replaced s with jw in laplace expression to determine freq response, is that the correct method, how can I use MATLAB to draw the reponse curves for magnitude and phase.

Thanks once again

Ashutosh
 

laplace second order filter

bode(tf([1],[L*C 0 1]));
This should give you the mag and phase response in MATLAB.
 
second order filters

Hi,
thanks for reply,
The selected component values theorotically gives correct freq response, but when connected the o/p gets -10dB at 1000Hz which actually has 3500Hz of cut off. Is the problem because of the characteristic impedance (or o/p impedance). Which is sqrt(L/C) very small about 4.4 Ohm.

Thanks again

Ashutosh
 

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