A varactor circuit and voltage-controlled oscillation are described. The varactor circuit includes a first varactor, a second varactor, a third varactor, and a fourth varactor. A first source-drain node of the first varactor and a second source-drain node of the second varactor are coupled to a first input node. A first gate node for the first varactor is coupled to a first output node. A second gate node for the second varactor is coupled to a second output node. A third gate node for the third varactor and a fourth gate node for the fourth varactor are coupled to a second input node. A third source-drain node of the third varactor is coupled to the first output node. A fourth source-drain node of the fourth varactor is coupled to the second output node. In other embodiments, varactor circuits block and re-center VCO output CML.