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.

A circuit including an amplitude detector. The amplitude detector includes an input to receive a signal having an amplitude voltage and a first pair of transistors configured in parallel. The input is coupled to the control terminal of at least one transistor of the first pair. The amplitude detector includes a first node providing a voltage indicative of the amplitude voltage. The first node is in series with each of the first pair of transistors. The circuit includes a compensation circuit. The compensation circuit includes a second pair of transistors configured in parallel and a second node. The second node is coupled in series with each transistor of the second pair. The circuit includes an amplifier including a first amplifier input coupled to the first node and a second amplifier input coupled to the second node.

A magnetoresistive effect oscillator executes a first step of applying a current, which has a first current density larger than a critical current density J.sub.O for oscillation, to a magnetoresistive effect element for a time T.sub.P, and then executes a second step of applying a current, which has a second current density J.sub.S smaller than the first current density and not smaller than the critical current density J.sub.O for oscillation, to the magnetoresistive effect element. The following formulae (1), (2) and (3), or the following formulae (1) and (4) are satisfied on an assumption that an average value of the first current density during the time T.sub.P in the first step is J.sub.P, a critical current density for magnetization reversal of the magnetoresistive effect element is J.sub.R, and a magnetization reversal time of the magnetoresistive effect element is T.sub.R: $\begin{array}{cc}\frac{0.1\times T_R\left(J_R-J_O\right)}{J_p-J_S}<T_p<0.9\times T_R\frac{J_R-J_O}{J_S-J_O}& \end{array}$

An oscillator includes: a first inductor; and a programmable capacitor bank coupled between a first terminal of the first inductor and a second terminal of the first inductor, where the programmable capacitor bank includes a plurality of cells concatenated together, where each cell of the plurality of cells includes a first node, a second node, a third node, a second inductor, and a programmable capacitor, where the second inductor is coupled between the first node and the third node, and the programmable capacitor is coupled between the third node and the second node, where a first inductance of the first inductor is larger than a sum of the inductances of the second inductors of the programmable capacitor bank.

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 voltage controlled oscillator (VCO) circuitry includes a varactor array. The varactor array includes a first varactor unit including a first varactor, a second varactor, and first switch circuitry. The first varactor is connected to a first node and a second node, and the second varactor is connected to the second node and a third node. The second node receives a voltage control signal. The first switch circuitry is electrically coupled to the first node and the third node, and selectively electrically couples a first voltage signal to the first node and the third node based on a first control 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.

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.

In accordance with an embodiment, a method includes: receiving, by an adjustable frequency doubling circuit, a first clock signal having a first clock frequency; using the adjustable frequency doubling circuit, generating a second clock signal having a second clock frequency that is twice the first clock frequency; measuring a duty cycle parameter of the second clock signal, where the duty cycle parameter is dependent on a duty cycle of the first clock signal or a duty cycle of the second clock signal; and using the adjustable frequency doubling circuit, adjusting the duty cycle of the first clock signal or the second clock signal based on the measuring.

A voltage controlled oscillator includes a resonator and an amplifier. The resonator includes a capacitive element and an inductive element. The inductive element has a plurality of conductive segments forming a physical loop. The inductive element has electrical connections on the physical loop to the plurality of conductive segments forming at least one electrical loop disposed within an interior space formed by the physical loop. The amplifier has an input and an output, the input coupled to a first conductive segment forming a first impedance and the output coupled to a second conductive segment forming a second impedance.