many electronic devices , such as computers and printers , communicate data to each other over wireline or wireless communications links . one component vital to such communications is a voltage - controlled oscillator — a circuit that outputs an oscillating signal having an oscillation frequency based on a control voltage . conventional vcos adjust frequency based on a single control voltage input , which makes them vulnerable to unintended changes in the control voltage these voltage changes cause frequency deviations that can make communications between devices less reliable . accordingly , the present inventors devised a vco that includes differential frequency control — frequency control based on the difference of two control voltages . the vco , which uses a differentially tunable impedance , rejects common - mode noise and thus bolsters reliability of communication circuits , such as phase - lock loops , receivers , transmitters , transceivers , and other devices that use it