A crystal oscillator is coupled to a digital automatic gain control (AGC) having oscillation detection and amplitude control loops. The oscillation detection loop may increase the transconductance (gm) of the oscillator transistor until oscillation is detected therefrom. Then the amplitude control loop detects the amplitudes of oscillations from the crystal oscillator, compares these amplitudes to high and low voltage references and generates digital signals to find a critical transconductance (gm) for an oscillator amplifier and control this gm to maintain a constant oscillation waveform amplitude therefrom. An up/down counter defines the servo control loop bandwidth/update-rate according to an update clock rate thereto. Loop stability is achieved when the control loop bandwidth is less than the start-up time required for the oscillation envelope of the crystal oscillator to grow for oscillation. An oscillator failure detector may also be provided.

A crystal oscillator device is disclosed. The crystal oscillator device includes: a crystal oscillator including a casing, a crystal piece, a pair of excitation electrodes configured to excite a main vibration, and a pair of sub vibration electrodes configured to excite a sub-vibration; and an alarm generator configured to generate an alarm based on a signal whose amplitude is equal to or less than a reference value, the signal being generated in the sub vibration electrodes.

A crystal oscillator device is disclosed. The crystal oscillator device includes a crystal piece provided in a casing; a pair of excitation electrodes provided for the crystal piece; a coil provided on the crystal piece; a magnetic flux generating member configured to generate magnetic flux passing through the coil; and an alarm generator configured to generate an alarm based on a signal whose amplitude is equal to or less than a reference value, the signal being generated in the coil.

A crystal oscillator device is disclosed. The crystal oscillator device includes: a casing; a crystal piece provided in the casing; a pair of excitation electrodes provided on the crystal piece; a magnetic flux generating member provided on the crystal piece; a coil through which magnetic flux from the magnetic flux generating member passes; and an alarm generator configured to generate an alarm based on a signal whose amplitude is equal to or less than a reference value, the signal being generated in the coil.

A crystal oscillator device is disclosed. The crystal oscillator device includes: a crystal piece provided in a casing; a pair of excitation electrodes provided on the crystal piece; a light emitting element configured to emit light that is to be reflected by one of the excitation electrodes to generate reflected light; a light receiving element configured to receive the reflected light; and an alarm generator configured to generate an alarm based on a signal upon an index value being less than or equal to a reference value, the signal being generated in the light receiving element, the index value representing an oscillation level of the crystal piece in an oscillating state.

A circuit includes: an oscillator configured to generate an oscillation clock signal; an NMOS transistor having a source connected with a power terminal of the oscillator, and a drain connected with a first power supply line to which a first power supply voltage is supplied; an operational amplifier configured to control a gate voltage of the NMOS transistor based on a voltage of the power terminal of the oscillator; and a charge pump.

The charge pump is configured to use the oscillation clock signal or a clock signal generated from the oscillation clock signal to boost the first power supply voltage and generate a boosted power supply voltage, and to supply the boosted power supply voltage to the power terminal of the operational amplifier.

A trigger, includes: a first voltage input terminal; a bias voltage input terminal; a first bias transistor having a scaling of N to a first component of an external device; a comparator transistor having a scaling of N to a second component of the external device; a first switch transistor and a second switch transistor; a shunt transistor having a control terminal connected to the first voltage input terminal, a second terminal connected to the second terminal of the second switch transistor, and a first terminal connected to the first terminal of the comparator transistor. The shunt transistor has an enlarging scale of M to the comparator transistor. A voltage output terminal is respectively connected to the second terminal of the first switch transistor, the control terminal of the second switch transistor, and the second terminal of the comparator transistor.

An oscillator circuit (100) comprises a crystal oscillator (10) arranged to generate an oscillation signal, a bias current generator (20) arranged to supply a bias current to the crystal oscillator (10), and a feedback stage (30) arranged to generate a feedback signal in response to an amplitude of the oscillation signal reaching an amplitude threshold. The bias current generator (20) is arranged to: in response to a supply of power to the oscillator circuit (100) being switched on, generate the bias current at an increasing level commencing from a first level; in response to the feedback signal, terminate the increasing; and during subsequent oscillation of the crystal oscillator (10), supply the bias current at a second level dependent on a final level of the bias current reached when the increasing is terminated.

An oscillator circuit comprises a crystal oscillator arranged to generate an oscillation signal, a bias current generator arranged to supply a bias current to the crystal oscillator, and a feedback stage arranged to generate a feedback signal in response to an amplitude of the oscillation signal reaching an amplitude threshold. The bias current generator is arranged to: in response to a supply of power to the oscillator circuit being switched on, generate the bias current at an increasing level commencing from a first level; in response to the feedback signal, terminate the increasing; and during subsequent oscillation of the crystal oscillator, supply the bias current at a second level dependent on a final level of the bias current reached when the increasing is terminated.

An oscillator circuit comprises a crystal oscillator arranged to generate an oscillation signal, a bias current generator arranged to supply a bias current to the crystal oscillator, and a feedback stage arranged to generate a feedback signal in response to an amplitude of the oscillation signal reaching an amplitude threshold. The bias current generator is arranged to: in response to a supply of power to the oscillator circuit being switched on, generate the bias current at an increasing level commencing from a first level; in response to the feedback signal, terminate the increasing; and during subsequent oscillation of the crystal oscillator, supply the bias current at a second level dependent on a final level of the bias current reached when the increasing is terminated.