Using Varactor in LC tank notch filter

[alimjoco]

Hi,

I want to use a speciifc notch filter using a tank circuit from input to output(series). If I wanted to tune the tank using varactor, back to back diodes, how can I connect the positive polarity of my supply assuming I connect the neg polarity at the middle on back to back diodes(reverse). The tank is series from input to output..

 

[biff44]

usually there is a inductor to ground at the input, and another one at the output, of the filter. Then you just apply the tune voltage to the center of the two varactor diodes, referenced to ground. You must be careful to not kill the Q of the tank with the bias line!

With this topology, you do not need series dc blocking caps.

 

[D.A.(Tony)Stewart]

schematic and Freq. would be useful. how much cap ratio or F range do you need? What Q? What distortion level?


Remember the better your question, the better the answer.

But in the meantime, try these answers. **broken link removed**

 

[alimjoco]

Thanks guys. Ive changed my mind in using varactors... Do anyone know about BST caps? Where can I buy that one? Do ther come in discrete pakages like normal caps?

 

[D.A.(Tony)Stewart]

What F and specs are you try to achieve in your BPF? Why tuneable?
Barium Strontium Titanate (BST) tuneable caps are exotic materials using in MLM and hybrids ( ie custom parts)