Oscillator Voltage Amplitude

For LC VCO's there are a few factors that limit the output voltage amplitude:
- The supply voltage
- The bias current
- The frequncy of oscillations
- The inductance of the inductor
- The tank resistance


If we increase the bias current of the VCO the amplitude will increase in direct proportion until the voltage will reach Vlimit.

Vout = Ibias * Rtank

This regime is called the Current Limited Regime.
Now if we keep increasing the bias current the VCO, the output swing will keep Vlimit (with a small change).

Vout = Vlimit

This regime is called the Voltage Limited Regime.