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Questions about Elliptic Gm-C LPF

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abcyin

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Elliptic Gm-C LPF

Hi, all

In elliptic gm-C filter, gyrators are used to substitute the ideal inductor, but I want to know how the gain bandwidth of the transconductors limits the bandwidth of the filter, that's to say, if the cutoff frequency of the LPF has been given by spec, then how much GBW of gm should be?

Could you give me some advice about that, or any literature about that are appreciated.

Thx in advance!
 

Re: Elliptic Gm-C LPF

The bandwidth of the transconductor will generally limit the stopband attenuation of your filter. The finite bandwidth of the gm adds an extra phase shift in the feedback paths of the filter. I would suggest a GBW that's at least 20 dB larger than your filter bandwidth.

some information about this excess phase can be found in

"A BiCMOS Low-Distortion 8 MHz Low Pass Filter", Scott D Willingham, IEEE JSSC, december 1993
 

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    abcyin

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Re: Elliptic Gm-C LPF

ce said:
The bandwidth of the transconductor will generally limit the stopband attenuation of your filter. The finite bandwidth of the gm adds an extra phase shift in the feedback paths of the filter. I would suggest a GBW that's at least 20 dB larger than your filter bandwidth.

some information about this excess phase can be found in

"A BiCMOS Low-Distortion 8 MHz Low Pass Filter", Scott D Willingham, IEEE JSSC, december 1993
Click to expand...

Thx for your reply, and I have another question during LPF design, I found that the parasitic capacitor of the trans-conductor cell is so disgusted, and the frequency response will be affected by the parasitics obviously, So, my question is how to reduce the effect of the parasitics to compensate the frequency response? by which way?

Thx again!
 

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