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 example voltage controlled oscillator includes an inductor, a capacitor coupled to the inductor, and a signal source coupled to the inductor and the capacitor to sustain an oscillating signal. The voltage controlled oscillator includes a first varactor coupled to the inductor and the capacitor, wherein the first varactor is biased by a first bias voltage and is configured to change a frequency of the oscillating signal based on a first control voltage signal. The voltage controlled oscillator includes a second varactor coupled to the inductor, the capacitor, and the first varactor, wherein the second varactor is biased by a second bias voltage and is configured to compensate temperature variation of the frequency of the oscillating signal over a plurality of frequency bands based on second control voltage signal.

A differential oscillator includes a differential circuit and a transformer-coupled band-pass filter (BPF) coupled between first and second output nodes. The BPF includes a coupling device coupled between the output nodes and a transformer including first and second windings in a metal layer of an IC. The first winding includes first and second conductive structures coupled to the first output node and a voltage node, respectively, and a third conductive structure including first and second extending portions connected to the first and second conductive structures, respectively. The second winding includes a fourth conductive structure including a third extending portion coupled to the voltage node and a fourth extending portion coupled to the second output node. The third extending portion is between the second conductive structure and the first extending portion, and the fourth extending portion is between the first conductive structure and the second extending portion.

An integrated circuit may include oscillator circuitry having a resonator formed from fin field-effect transistor (FinFET) devices. The resonator may include drive cells of alternating polarities and sense cells interposed between the drive cells. The resonator may be connected in a feedback loop within the oscillator circuitry. The oscillator circuitry may include an amplifier having an input coupled to the sense cells and an output coupled to the drive cells. The oscillator circuitry may also include a separate inductor and capacitor based oscillator, where the resonator serves as a separate output filter stage for the inductor and capacitor based oscillator.

A band-pass filter (BPF) includes a pair of coupled transformers including first through fourth conductive structures. The first conductive structure includes a first terminal and two first extending portions extending from the first terminal and configured as primary windings. The second conductive structure includes a second terminal and two second extending portions extending from the second terminal. A first via connects the third conductive structure to a first one of the two second extending portions, the third conductive structure and the first one of the two second extending portions thereby being configured as a first secondary winding. A second via connects the fourth conductive structure to a second one of the two second extending portions, the fourth conductive structure and the second one of the two second extending portions thereby being configured as a second secondary winding.

A system includes a data path and a phase-locked loop (PLL) coupled to the data path. The system also includes a voltage-controlled oscillator (VCO) coupled to the PLL. The VCO includes an LC circuit with first and second differential output terminals. The VCO also includes a first resistor coupled between the first differential output terminal and drain terminals of a first pair of complementary metal-oxide semiconductor (CMOS) transistors. The VCO also includes a second resistor coupled between the second differential output terminal and drain terminals of a second pair of CMOS transistors.

A variable capacitor device comprises first and second control paths which are configured to enable differential control using first and second transistors of a same doping type in the first and second control paths, respectively, wherein the first and second transistors are configured as voltage variable resistors for tuning a capacitance of the variable capacitor device.

An oscillator includes a forward stage including first and second terminals and a transformer-coupled band-pass filter (BPF) coupled between the first and second terminals and including a coupling device between the first and second terminals, and a transformer including first and second windings in a metal layer of an IC. The first winding includes a first conductive structure coupled to the first terminal and a second conductive structure coupled to a voltage node, a third conductive structure including first and second extending portions connected to the first and second conductive structures. The second winding includes a fourth conductive structure including a third extending portion coupled to the voltage node, and a fourth extending portion coupled to the second terminal. The third extending portion is between the second conductive structure and the first extending portion, and the fourth extending portion is between the first conductive structure and the second extending portion.

An oscillator circuit includes a total of N (N≥2) class-D oscillator circuits stacked together between a supply voltage node and a reference voltage node. The output ports of adjacent class-D oscillator circuits in the disclosed oscillator circuit are coupled together by capacitors to ensure frequency and phase synchronization for the frequency signals generated by the class-D oscillator circuits. Compared with a reference oscillator circuit formed of a single class-D oscillator circuit, the oscillation amplitude of each of the class-D oscillator circuits in the disclosed oscillator circuit is 1/N of that of the reference oscillator circuit, and the current consumption of the disclosed oscillator circuit is 1/N of that of the reference oscillator circuit.

An oscillator circuit includes a total of N (N≥2) class-D oscillator circuits stacked together between a supply voltage node and a reference voltage node. The output ports of adjacent class-D oscillator circuits in the disclosed oscillator circuit are coupled together by capacitors to ensure frequency and phase synchronization for the frequency signals generated by the class-D oscillator circuits. Compared with a reference oscillator circuit formed of a single class-D oscillator circuit, the oscillation amplitude of each of the class-D oscillator circuits in the disclosed oscillator circuit is 1/N of that of the reference oscillator circuit, and the current consumption of the disclosed oscillator circuit is 1/N of that of the reference oscillator circuit.