One inductor and another inductor are magnetically coupled to each other. A variable current source controls the current flowing in the one inductor. By controlling the current flowing in the one inductor, the inductance value of the other inductor is made variable.

A tunable impedance multiplier with high multiplication factor is described. A single externally connected resistor is used and the multiplier is free of passive elements. The circuit can realize a positive or a negative impedance multiplier. Applications of the design to low and high pass filters are also presented. The simulation and experimental results show that the new design enjoys a multiplication factor above 400 at 2 Hz-to 7 MHz.

Various embodiments for controlling a resonant frequency of a resonator are described. A system includes at least one resonant circuit and an active variable reactance circuit that controls a resonant frequency of the at least one resonant circuit. The active variable reactance circuit includes an electrically-controllable switching element and a switch controller sub-circuit configured to switch the electrically-controllable switching element at a frequency of a radio-frequency (RF) current or voltage passing through or across a device such that the RF current flowing from a first terminal to a second terminal is substantially sinusoidal.

A tunable impedance multiplier with high multiplication factor is described. A single externally connected resistor is used and the multiplier is free of passive elements. The circuit can realize a positive or a negative impedance multiplier. Applications of the design to low and high pass filters are also presented. The simulation and experimental results show that the new design enjoys a multiplication factor above 400 at 2 Hz-to 7 MHz.

A combined mixer and filter circuitry is disclosed. The combined mixer and filter circuitry comprises a mixer comprising a first input, a second input and an output. The combined mixer and filter circuitry further comprises a filter comprising an active inductor and a first capacitor. The active inductor comprises a transistor having a first terminal, a second terminal and a third terminal and a resistor connected between the first terminal of the transistor and a voltage potential. The first capacitor is connected between the third terminal and a signal ground and the second terminal of the transistor is connected to the second input of the mixer.

A tunable impedance multiplier with high multiplication factor is described. A single externally connected resistor is used and the multiplier is free of passive elements. The circuit can realize a positive or a negative impedance multiplier. Applications of the design to low and high pass filters are also presented. The simulation and experimental results show that the new design enjoys a multiplication factor above 400 at 2 Hz-to 7 MHz.

A tunable impedance multiplier with high multiplication factor is described. A single externally connected resistor is used and the multiplier is free of passive elements. The circuit can realize a positive or a negative impedance multiplier. Applications of the design to low and high pass filters are also presented. The simulation and experimental results show that the new design enjoys a multiplication factor above 400 at 2 Hz-to 7 MHz.

A negative capacitance circuit is connected between a drain and a source of the mixer transistor. With this configuration, the negative capacitance circuit is connected in parallel to a parasitic capacitance generated between the drain and the source of the mixer transistor, and the parasitic capacitance can be canceled out in a wide band by the negative capacitance circuit connected in parallel.

An electronic emulation component for actively emulating a passive electronic component such as a capacitor or inductor having a desired value, comprises a pair of terminals for connection to an external circuit and across which the desired value is to appear, a power convertor, and a passive electronic component of the type to be emulated but having a value different from the value to be emulated and isolated from the pair of terminals by the convertor.

An electronic emulation component for actively emulating a passive electronic component such as a capacitor or inductor having a desired value, comprises a pair of terminals for connection to an external circuit and across which the desired value is to appear, a power convertor, and a passive electronic component of the type to be emulated but having a value different from the value to be emulated and isolated from the pair of terminals by the convertor.