In certain power applications, it is desirable to vary the amount of inductance in a circuit. For example, in a circuit that has a time varying capacitive load or a varying frequency of operation, the circuit may be tuned by varying the inductance to minimize the reactive current required to be supplied by a power source. Generally, in order to vary characteristics of an electronic circuit, characteristics of an active element or a value of a passive element included in the circuit is changed. For the active element, the characteristics of the active element can be changed by changing a bias voltage applied to the active element. For the passive element, a passive element, for example, a variable resistive element can be easily realized by using ON resistance of a MOSFET, and a variable capacitive element can be easily realized by using a pn junction. Variable inductors are of use in many circuit applications including magnetic amplifiers which vary the inductance of a circuit element to regulate power and resonant circuits which vary the inductance of circuit elements to vary the resonant frequency of the circuit. Variable inductors are useful and required circuit elements in a variety of important applications and products. For example, inductors and variable inductors are necessary elements of many RF-wireless products. In particular, they are used for matching and loading low noise amplifiers, power amplifiers and mixers, as well as for providing frequency- selective resonant circuits in variable-frequency oscillators in such RF-wireless products.
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