A crystal oscillator and a startup method for initiating operation of a crystal oscillator with a crystal resonator including a first terminal and a second terminal, an electronic oscillator circuit connected to the crystal resonator, a first capacitor including first and second terminals, the second connected to the first terminal of the crystal resonator, a second capacitor including first and second terminals, the second connected to the second terminal of the crystal resonator. A switch includes first, second and third terminals, wherein an electrical conductivity between the first terminal and the second terminal of the switch is controllable by a voltage at the third terminal, wherein the first terminal of the switch is connected to the first terminal of the first capacitor and wherein the second terminal of the switch is connected to the first terminal of the second capacitor.

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.

A circuit and method for starting-up a crystal oscillator is described. A crystal resonator is configured to be coupled to a start-up circuit including an H-bridge circuit having a number of switches. A plurality of switch control signals are generated in response to detecting a zero-crossing event of the motional current in the crystal resonator. The switches of the H-bridge circuit are controlled by the switch control signals to apply a voltage to the terminals of the crystal resonator in a first polarity during a first switch control phase and a second opposite polarity during a second switch control phase. During a respective first subphase of the respective switch control phase, the plurality of switches are configured in a first configuration to couple the supply node to a respective crystal resonator terminal. During a respective second subphase of the respective switch control phase the plurality of switches are configured in a second configuration to couple the supply node to the respective crystal resonator terminal. The resistance between the supply node and the respective crystal resonator terminal is larger in the second configuration than the first configuration. A zero-crossing is detected during each respective second sub-phase.

A crystal oscillator and a startup method for initiating operation of a crystal oscillator, the crystal oscillator includes an oscillator structure including a crystal resonator and an electronic oscillator circuit connected to the crystal resonator, the oscillator structure having a first terminal and a second terminal, a startup controller operable to initiate an oscillation in the oscillator structure by exciting the oscillator structure with a sequence of excitation signals derivable from a clock signal and when triggered by a timing signal, the sequence of excitation signals includes at least a first excitation signal and a second excitation signal, a comparator including a first and a second input terminal and an output terminal, the first input terminal being connected to the first terminal and wherein the second input terminal is connected to the second terminal.

Oscillator quick-startup circuit and method in which a voltage step is applied to a resonator (crystal) resulting in ringing which is amplified and fed into a locking circuit which locks to it, such as a programmable delay circuit. Once locking is complete, then the circuit is switched into a standalone oscillator mode, having a feedback path, the output of this injection oscillator energizes the resonator for achieving quick startup of a primary oscillator, in response to it automatically adjusting injection oscillator frequency to match the frequency of the resonator. A digital circuit controls the configuring of the circuit for applying the voltage step, adjusting the locking circuit, and then switching into a standalone oscillator mode.

Disclosed is an integrated circuit amplifier for use in a crystal oscillator. The circuit amplifier comprises a transistor; a voltage dependent capacitance circuit; and a node. The voltage dependent capacitance circuit comprises a device with a voltage dependent capacitance and a bias circuit. The node is connected to a terminal of the transistor and the integrated circuit amplifier is configured such that an intrinsic capacitance of the transistor is dependent on the mean voltage at the node. The node is connected to a terminal of the voltage dependent capacitance circuit and the integrated circuit amplifier is configured such that an effective capacitance of the node is dependent on the intrinsic capacitance of the transistor and the voltage dependent capacitance of said device. When in use, the voltage dependent capacitance circuit reduces the amount of change of the effective capacitance of the node when the mean voltage at the node changes.

An apparatus injects a start clock to a crystal at the beginning to increase an overall start up speed of the crystal. The apparatus relies on an impedance change inside the crystal itself instead of searching for a synchronization on the yet small crystal oscillation. The apparatus includes an oscillator (separate from the crystal) to search for the crystal's resonance frequency by detecting the crystal's impedance change. Once the frequency of the oscillator matches the crystal's resonance, there is significant change in the crystal's impedance. Using that information, the apparatus can lock the oscillator frequency at the crystal resonance frequency and inject the clock with high efficiency.

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.

A first switch is operable to couple a start-up oscillator circuit to a first crystal pin during operation in a start-up mode and decouple the start-up oscillator circuit from the first crystal pin during operation in a normal mode, and a second switch is operable to couple the start-up oscillator circuit to a second crystal pin during operation in the start-up mode and decouple the start-up oscillator circuit from the second crystal pin during operation in the normal mode. A switched oscillator circuit is coupled to the startup oscillator during operation in the startup mode, and to the first and second crystal pins during operation in the start-up and normal modes. The switched oscillator circuit includes a sample and charge circuit which is configured to sample a direct current (DC) level of the first crystal pin and pre-charge a first coupling capacitor during operation in the startup mode.

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.