The VCO is exactly the same as the PA except for a few
differences. This matching of the two circuits is critical to the
master-slave tuning. The first difference is that the VCO does not
have an input signal so there is no cascode input stage. Second,
the capacitor in the tank circuit is smaller so that the frequency of the
oscillator is higher than the center frequency of the PA/filter by the
IF. This also ensures that when the oscillator goes into oscillation
that the PA does not. The final difference is that the diode connected
FET, M3, is narrower. The reason for this is to match the VCO to
the PA by keeping the voltage drop across M3 the same for both circuits.
Since there is less current flowing through M3 in the VCO due to no input
stage, it must be narrower to drop the same voltage as the FET in the PA.