VCO design quuestion (centre frequency)

[kumite]

Hello,
I have alittle question in vco design that may be seen as very basic but it is very confusing for me , i am designing vco with tail baised lc oscillator with discrete tuning (fine and coarse) so at the start should i design the tank to oscillate at the max frequency of oscillation and then by using varactor i can sweep across the tuning range or to design it(tank) at the centre frequency and then, how can i sweep the range from min to max knowing that iam initially at the centre ? And the capacitance of the varactor is only increasing or decreasing.
Any help would be appreciated.
Thanks in advance .

 

[chuckey]

You have to first decide on the varactor, either max or min capacity. If minimum capacity, add a bit on for stray capacity. Now work out your inductance for the maximum frequency. Repeat using figure for varactor max cap (+stray C) and if you are in luck it will be lower frequency then required. if not you need a better varactor. remember, you need 4:1 cap for 2:1 freq (square law)
Frank