Patent ID: 7019597

Claim:
A method for improving common mode noise rejection in an AC output signal generated by a voltage controlled oscillator, the AC output signal being generated in proportion to a differential input control signal, the differential input control signal having a high input and a low input, the high input and the low input each having a DC component and an AC component, the method comprising: providing the differential input control signal to a varactor circuit, the varactor circuit having differential input nodes and differential output nodes; generating a differential output having a DC component and an AC component; tuning an LC tank by the AC component of the differential output, the LC tank being coupled to the differential output nodes of the varactor circuit through AC coupling capacitors, the AC coupling capacitors being capable of blocking the DC component of the differential output; blocking tho DC component of the differential output by coupling the AC coupling capacitors between the differential output nodes of the varactor circuit and the LC tank; and applying the AC component to an active circuit, the active circuit having terminals coupled with the LC tank, wherein each of the AC coupling capacitors includes a first capacitor coupled between the LC tank and one of the differential output nodes of the varactor circuit, a second capacitor coupled between the same one of the differential output nodes of the varactor circuit and ground, and a resistor coupled between the second capacitor and ground.