A voltage controlled oscillator includes a first inductor; a first variable capacitance unit including a first variable capacitance element having a variable capacitance and a second variable capacitance element having a variable capacitance; a first node configured for application of a first voltage to the first variable capacitance unit; a cross-coupled unit including a first transistor and a second transistor, an output of the first transistor connected to an input of the second transistor; a current source configured to flow a current through the first inductor, the first transistor, and the second transistor; a second variable capacitance unit including a third variable capacitance element having a variable capacitance, and a fourth variable capacitance element having a variable capacitance; and a second node different from the first node configured for application of a second voltage to the second variable capacitance unit.

An ultra-low noise crystal oscillator uses two crystal unit; an oscillation element of an oscillation circuit section and a crystal filter of a subsequent filter section. A Butler circuit in which the capacitors (C1, C2) and the inductor (L) connected in series is connected in parallel to the oscillator circuit section. This is the crystal oscillator that simplifies the manufacturing process, improves the manufacturing quality, and has good floor noise characteristics.

An ultra-low noise crystal oscillator uses two crystal unit; an oscillation element of an oscillation circuit section and a crystal filter of a subsequent filter section. A Butler circuit in which the capacitors (C1, C2) and the inductor (L) connected in series is connected in parallel to the oscillator circuit section. This is the crystal oscillator that simplifies the manufacturing process, improves the manufacturing quality, and has good floor noise characteristics.

A voltage controlled oscillator includes a first inductor; a first variable capacitance unit including a first variable capacitance element having a variable capacitance and a second variable capacitance element having a variable capacitance; a first node configured for application of a first voltage to the first variable capacitance unit; a cross-coupled unit including a first transistor and a second transistor, an output of the first transistor connected to an input of the second transistor; a current source configured to flow a current through the first inductor, the first transistor, and the second transistor; a second variable capacitance unit including a third variable capacitance element having a variable capacitance, and a fourth variable capacitance element having a variable capacitance; and a second node different from the first node configured for application of a second voltage to the second variable capacitance unit.

Various technologies described herein pertain to non-inverting multi-mode oscillators. An oscillator circuit can include a non-inverting sustaining amplifier and a feedback network. The non-inverting sustaining amplifier includes an amplifier input and an amplifier output. The feedback network includes a crystal, an input portion, and an output portion. The crystal of the feedback network can be connected between the amplifier input and the amplifier output of the non-inverting sustaining amplifier. The input portion of the feedback network can be connected between the amplifier input and ground, and can include an inductor realized using a tank circuit. Further, the output portion of the feedback network can be connected between the amplifier output and ground, and can include a capacitor. Moreover, the crystal can operate in series resonance mode or parallel resonance mode.