Strange response of 4-pole gaussian BPF

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Strange Filter Response!

Hi

I have designed a 4-pole gaussian BPF arround 455kHz with 10kHz 3dB BW. I have tested it response and found that the sharpness is good but the insertion loss is about 30dB.
I guessed this insertion loss was due self resonance of the 680nF capacitor, but i have tested it response and found the resonance frequency is equal to 3.5MHz.
What is my fault can anyone help me?

Best Regards
 

Re: Strange Filter Response!

Make C11 and L11 a series resonant circuit. In their parallel form they block the signal flow at their resonant frequency.
 

Re: Strange Filter Response!

Hi

Sorry, I have mistake. C11 and L11 are in series form.
Is there any mistake?

Regards
 

Re: Strange Filter Response!

What is the value of C12? Is it 680nF?
Could you please re-draw the actual diagram of your filter with correct values !!! 8)
 

Re: Strange Filter Response!

Hi

Here is the corrected version of the schematics.
The value of the C12 is 680nF.

Regards
 

Re: Strange Filter Response!

You have imbalance in the parrallel cell: the C value is to big and the L value is to small.
Try to balance them in such a way that their impedances at 455kHz are comparable.
 

Re: Strange Filter Response!

Hi

Thanks for replies.
I can not balance value of the L and C, as you know the ratio of the L/C change the BW. So i can not change value of the L and C.

Regards
 

Strange Filter Response!

Those are very high-Q resonant circuits. You'll need super parts!
With one volt input and ideal components (unlikely), you get up to 30 volts at node 1, and one ampere through L12.

Code: 
PSpice simulation

Vin   5  0  AC 1.0V
Rin   5  6  50
C11   6  1  180pF
L11   1  2  680uH
L12   2  0  180nF
C12   2  0  680nF
Rout  2  0  50

.AC DEC 5000 400kHz 500kHz
.PROBE
.END
 

Re: Strange Filter Response!

Hi

Thank you very much.
what can i do to design such a filter?

Best Regards
 

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