In one form, an oscillator includes an oscillator core circuit and a dynamic gain control circuit. The oscillator core circuit is for connection to a frequency reference element and provides a first clock signal using a negative gain element having a gain determined by a gain control signal. The dynamic gain control circuit is coupled to the oscillator core circuit for calibrating the gain control signal to a startup value based on oscillations reaching a first threshold during a startup state, and calibrating the gain control signal to a steady-state value based on oscillations falling to a second threshold after an end of the startup state and before entering a steady state. The first threshold is higher than the second threshold. The dynamic gain control circuit operates the oscillator core circuit during the steady state using the steady-state value.

In one form, an oscillator includes an oscillator core circuit and a dynamic gain control circuit. The oscillator core circuit is for connection to a frequency reference element and provides a first clock signal using a negative gain element having a gain determined by a gain control signal. The dynamic gain control circuit is coupled to the oscillator core circuit for calibrating the gain control signal to a startup value based on oscillations reaching a first threshold during a startup state, and calibrating the gain control signal to a steady-state value based on oscillations falling to a second threshold after an end of the startup state and before entering a steady state. The first threshold is higher than the second threshold. The dynamic gain control circuit operates the oscillator core circuit during the steady state using the steady-state value.

A crystal amplifier for driving a crystal to oscillate at a resonant frequency including a controlled current source, a primary amplifier core, a high gain amplifier core, and a controller. Both amplifier cores are coupled in parallel, and each has an input coupled to an amplifier input node and an output coupled to an amplifier output node coupled across the crystal. The current source provides a core bias current to the source node. The controller enables the high gain amplifier core and sets the core bias current to a high current level to achieve a high negative resistance at a startup time, and then disables the high gain amplifier core and sets the core bias current to a lower steady state current level after oscillation is achieved. A level detector may be used for detecting oscillation and for determining when to adjust the core bias current.

A crystal amplifier for driving a crystal to oscillate at a resonant frequency including a controlled current source, a primary amplifier core, a high gain amplifier core, and a controller. Both amplifier cores are coupled in parallel, and each has an input coupled to an amplifier input node and an output coupled to an amplifier output node coupled across the crystal. The current source provides a core bias current to the source node. The controller enables the high gain amplifier core and sets the core bias current to a high current level to achieve a high negative resistance at a startup time, and then disables the high gain amplifier core and sets the core bias current to a lower steady state current level after oscillation is achieved. A level detector may be used for detecting oscillation and for determining when to adjust the core bias current.

A start-up circuit for a ring current-controlled oscillator (CCO) includes a replica CCO current generator, a replica ring CCO, and a buffer. The ring CCO is connected to a CCO driver and the buffer. The CCO driver generates a CCO current based on a reference current. The ring CCO generates a CCO output voltage at a first oscillating frequency based on the CCO current. The replica CCO current generator generates a replica CCO current based on a reference voltage. The replica ring CCO generates a replica CCO output voltage at a second oscillating frequency based on the replica CCO current. The buffer provides a first current to the ring CCO when the first oscillating frequency is lower than a desired oscillating frequency, and drains a second current from the ring CCO when the first oscillating frequency is greater than the desired oscillating frequency.

A start-up circuit for a ring current-controlled oscillator (CCO) includes a replica CCO current generator, a replica ring CCO, and a buffer. The ring CCO is connected to a CCO driver and the buffer. The CCO driver generates a CCO current based on a reference current. The ring CCO generates a CCO output voltage at a first oscillating frequency based on the CCO current. The replica CCO current generator generates a replica CCO current based on a reference voltage. The replica ring CCO generates a replica CCO output voltage at a second oscillating frequency based on the replica CCO current. The buffer provides a first current to the ring CCO when the first oscillating frequency is lower than a desired oscillating frequency, and drains a second current from the ring CCO when the first oscillating frequency is greater than the desired oscillating frequency.

A clock generation circuit includes: a two-phase clock generation circuit configured to generate a first phase clock signal and a second phase clock signal based correspondingly on a non-inverted clock signal and an inverted clock signal, the first phase clock signal and the second phase clock signal exhibiting non-overlapping logical high states; an inverter configured to generate the inverted clock signal based on an input clock signal; and a delay circuit which is non-inverter-based and which is configured to generate the non-inverted clock signal based on the input clock signal, the delay circuit having a predetermined delay sufficient to cause a difference between a first duration and a second duration within a clock cycle to be less than a predetermined tolerance.

Embodiments can provide individualized controlling of noise injection during startup of a crystal oscillator. In some embodiments, a simple learning block can be placed in parallel to a oscillator circuit to control noise injection during the startup of the crystal oscillator. The learning block can be configured to control the noise injection during the startup of the crystal oscillator by determining whether the crystal oscillator has been stabilized. In some embodiments, an adjustment block may be employed to adjust the count determined by the learning block based on one or more measured characteristics of the crystal oscillator during a startup of the crystal oscillator. In some embodiments, a simple block that creates a negative capacitance can be configured in parallel to the crystal oscillator.

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 (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.