[SOLVED] second order filter design

[ashugtiwari]

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

 

[mengcy]

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!

 

[ashugtiwari]

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

 

[saro_k_82]

laplace second order filter

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

 

[ashugtiwari]

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