An electrical circuit includes: at least one inductor, at least one varactor, and at least two transistors, all of which electrically arranged to form a voltage controlled oscillator (VCO) having an oscillation frequency; wherein the at least two transistors includes a first transistor and a second transistor; wherein the first transistor has a first bulk terminal and a first parasitic diode disposed between the first bulk terminal and the first transistor; wherein the second transistor has a second bulk terminal and a second parasitic diode disposed between the second bulk terminal and the second transistor; wherein application of a first control voltage to the first bulk terminal, application of a second control voltage to the second bulk terminal, or application of first and second control voltages to the first and second bulk terminals, respectively, is effective to change the oscillation frequency of the VCO.