VCO of ranges from 925-960 and 1805-1880MHZ
Colpitts,Clapp,Hartley or any other you suggest!
and why you suggest this?
please tell me i need your help?!
and plz provide formula of oscillator u sugest..
thanks all.
It all comes down to the loaded Q of the resonator. With this narrow frequency range, you could consider using a coaxial resonator (Trans-Tech has a wide range), and couple the tuning varactor very lightly. You can find many examples on the web using Collpits topology.
One idea which might work: you could consider using a single VCO @ 1.8 GHz and use a divider (called prescaler at those frequencies) to generate the tunable 900 MHz. Saves you an additional varactor and synthesizer!
From provided frequency range seems that you are looking for a VCO, part of a direct up-conversion transmitter for GSM900 and DCS1800. If is a direct up-conversion, you need a VCO with a low wide-band noise, to don?t use very special TX filters.
Whatever topology you use, the quality factor of the resonant circuit is important, this including: Q of the resonator, series resistance of capacitors, series resistance of the tuning diode, the loss of printed circuit board, etc. Generally Colpitts is the most used for this kind of application.