Notch filter using negative resitance

[stenzer]

Hi,

I'm trying to realize a "narrow" notch filter which should operate in the lower MHz - range. Therefore I need a large inductance. This results in a low Q.
I read that it is possible to enhance the Q by adding a negative resistance with a transistor.

Can anyone tell my how to design such a filter?

Thanks

 

[vfone]

Yes is possible to do this mechanism to enhance the Q of the resonator. The circuit is basically a feedback amplifier with variable gain.

 

[BradtheRad]

If we take a simple LC tank as a notch filter...

Q is a result of L:C ratio interacting with neighboring impedances.



The available current has a lot to do with determining which LC ratio will be most suitable.

 

[stenzer]

Hi,

thank you for your replies. I tried to realize the negative resistance with a current sink, by changing its Drain voltage. Unfortunately it doesn't work well. Is there a better (and simple) way do enhance the Q?

BR