cmos varactor

A physical model of a CMOS varactor with high
capacitance tuning range in multi-finger layout is presented.
The model describes the voltage dependent capacitances and
resistances and the parasitics due to connecting wires.
Simulations of frequency tuning of a LC-oscillator employing
the varactor are verified against measurements.

free download at…
See this is a good paper too

A 80GHz voltage controlled oscillator is presented.
A passive impedance transformation enables the transformation
of a varactor capacitance into negative capacitance varactor is
proposed, partially canceling the capacitance of the differential
pair. This enables the transmission line resonator to be longer
and have a higher impedance. Design criterion for achieving
negative varactor capacitance is also presented, and design issues
of millimeter wave voltage controlled oscillators are discussed.
The voltage controlled oscillator is fabricated in 90nm CMOS
technology and achieves a phase noise of