In accordance with an embodiment, an oscillator circuit includes: a main current path coupled between a supply voltage terminal and a ground terminal, the main current path including a parallel resonant circuit, a load current path of a first transistor and a load current path of a second transistor. The parallel resonant circuit includes an inductor formed by a primary winding of a transformer, and a first capacitor; a terminal of the inductor is connected to the ground terminal; the load current path of the first transistor is coupled between the parallel resonant circuit and the load current path of the second transistor; and the parallel resonant circuit is coupled to a control electrode of the second transistor via a feedback path that includes a second capacitor.

A variable capacitor circuit includes a capacitor block including a first varactor element comprising a first transistor having a first size, a second varactor element comprising a second transistor having a second size different from the first size, a first terminal commonly connected to a source and a drain of the first transistor, a second terminal commonly connected to a source and a drain of the second transistor, and an RC circuit connected to a gate of the first transistor and a gate of the second transistor.

An oscillator configured to generate an oscillation signal is provided. The oscillator includes a transistor pair and a cross-coupled transistor pair. The transistor pair is coupled to a first current source and has a first transconductance. The first transconductance is changed in response to a current value of the first current source. The cross-coupled transistor pair is coupled to a second current source and has a second transconductance. The second transconductance is changed in response to a current value of second current source. The transistor pair and the cross-coupled transistor pair are mutually coupled by a plurality of inductors. A frequency of the oscillation signal is determined according to the first transconductance and the second transconductance. Furthermore, a clock generator and a method for generating a clock signal thereof are also provided.

A dual-band voltage controlled oscillator (VCO) includes: a first oscillator circuit including a first inductor; a second oscillator circuit including a second inductor; a first mode switch configured to electrically connect or disconnect a first output terminal of the first oscillator circuit and a first output terminal of the second oscillator circuit; a second mode switch configured to electrically connect or disconnect a second output terminal of the first oscillator circuit and a second output terminal of the second oscillator circuit; a third mode switch configured to electrically connect or disconnect a first terminal of the first inductor and a first terminal of the second inductor; and a fourth mode switch configured to electrically connect or disconnect a second terminal of the first inductor and a second terminal of the second inductor.

Apparatus and methods for power amplifiers with an injection-locked oscillator driver stage are provided herein. In certain configurations, a multi-mode power amplifier includes a driver stage implemented using an injection-locked oscillator and an output stage having an adjustable supply voltage that changes based on a mode of the multi-mode power amplifier. By implementing the multi-mode power amplifier in this manner, the multi-mode power amplifier exhibits excellent efficiency, including when the voltage level of the adjustable supply voltage is relatively low.

A voltage-controlled oscillator, including a voltage-controlled LC resonator including at least one first output node; an amplifier including at least one first dual-gate MOS transistor including first and second gates, coupling the first output node to a second node of application of a reference potential; and a regulation circuit capable of applying to the second gate of the first transistor a bias voltage variable according to the amplitude of the oscillations of a signal delivered on the first output node of the oscillator.

A frequency doubler (tripler, or quadrupler) employs current re-use coupled oscillator technique to enhance phase noise without increasing current consumption. Frequency doubler uses coupling between two oscillators running at different frequencies; a first oscillator is running at the target frequency and a second oscillator is running at half the frequency. The coupling between the two oscillators is via a transformer having a primary transformer coil and a secondary transformer coil. The first oscillator comprises a differential inductor, coarse/fine tuning capacitor arrays, and an n-type trans-conductor (GM). A virtual ground node of the n-type GM is coupled to one side of the primary transformer coil and the other side of the primary coil is coupled to the center tap of the secondary coil. The second oscillator comprises the secondary coil, coarse/fine tuning capacitor arrays, n-type GM, frequency tracking loop (FTL) and 2.sup.nd-harmonic LC filter network.

A semiconductor device according to the present embodiment includes a plurality of switching elements and a plurality of variable capacitance elements. The switching elements are switching elements connected in series between a first control terminal and a second control terminal and plural types of capacitance control signals can be supplied to the first control terminal and the second control terminal. The variable capacitance elements have capacitance control terminals connected to corresponding one ends of the switching elements, respectively.

A DC-DC converter includes: an transformer having a primary winding and a secondary winding magnetically coupled to the primary winding; a power oscillator applying an oscillating signal to the primary to transmit a power signal to the secondary winding; a rectifier connected to the secondary winding of the transformer to obtain an output DC voltage by rectification of the power signal; comparison circuitry to generate an error signal representing a difference between the output DC voltage and a reference voltage; a transmitter connected to the secondary winding of the transformer to apply an amplitude modulation to the power signal at the secondary winding of the transformer in response to the error signal to thereby produce an amplitude modulated signal at the primary winding; and a receiver and control circuit connected to the primary winding to control an amplitude of the oscillating signal as a function of the amplitude modulated signal.

Quadrature oscillator circuitry, comprising: a first differential oscillator circuit having differential output nodes and configured to generate a first pair of differential oscillator signals at those output nodes, respectively; a second differential oscillator circuit having differential output nodes and configured to generate a second pair of differential oscillator signals at those output nodes, respectively; and a cross-coupling circuit connected to cross-couple the first and second differential oscillator circuits. The cross-coupling circuit may comprise a pair of cross-coupled transistors.