Enhance the Speed of LC-VCO

The simplest way to increase the speed of LC-VCO is to reduce the inductance of the tank.

Thus, in theory, we can oscillate really fast.

However, I guess we trade something off for faster speed. What is the price? What is the criterion in choosing inductor value?

Thanks,
Neoflash

Using low LC ratio (together with Hi-Q inductor) it will reduce the LO phase noise.
There is a limit for this reduction to keep the oscillator running (is about the RF voltage across the resonator).

For integrated oscillators, By tuning your oscillator with a DC voltage, you already increase or decrease your speed of VCO. During your design you should define the band of your interest. This is generally done with changing the capacitance by varactors instead of changing the inductance. Because tuning a capacitor is much easier than tuning an inductor. Since these varactors are MOSFET capacitor, the high and low limits are the Depletion and accumulation region Capacitances in a MOSFET. This is about a Cmax/Cmin of about 3 or 4 for an integrated MOS varactor