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 method is provided for enhancing the detection of the start time of a reference oscillator (4) of a super-regenerative receiver (1), which includes the reference oscillator, a bias current generator (7), an oscillation detector (6), and an impedance matching unit (3). Following the supply of the bias current (i_vco) after receiving the activation control signal (Sosc), an oscillation detection is performed by the oscillation detector (6), and once oscillation is detected, an additional amplification current (iboost) dependent on the envelope of the detected oscillation, of an amplification current generation circuit is supplied to the reference oscillator (4) in addition to the bias current to amplify the oscillation signal to be above a critical oscillation start threshold so as to precisely define the start time of the oscillator, and enable the oscillation detector (6) to order the stoppage of oscillation of the reference oscillator (4).

A system includes a power driver, configured to generate an electric excitation; an oscillating system, configured to perform an oscillation induced by the electric excitation; a feedback detector, configured to detect a feedback measurement signal with to the oscillation; and a controller configured to operate: in a closed loop mode, to control the power driver to generate the electric excitation as a discontinuous electric excitation according to timing information obtained from the detected feedback measurement signal, to synchronize the discontinuous electric excitation with the detected feedback measurement signal; in a learning mode preceding the closed loop mode, to control the power driver to generate the electric excitation as a continuous electric excitation, to obtain timing information from the feedback measurement signal to be used, at least once, in the subsequent closed loop mode, to synchronize the discontinuous electric excitation with the detected feedback measurement signal.

A method of operating an oscillator circuit comprising a resonator is provided. The method comprises maintaining a resonance of the resonator by a) connecting the resonator to an input voltage (V.sub.buf) for a first pulse period to charge the resonator only partially towards the input voltage (V.sub.buf); b) connecting the resonator to a second, lower, voltage for a second pulse period to discharge the resonator at least partially; and repeating steps a) and b) at a rate corresponding to the resonance of the resonator and with a phase corresponding to the resonance of the resonator, so as to maintain the resonance of the resonator.

A method is provided for enhancing the detection of the start time of a reference oscillator (4) of a super-regenerative receiver (1), which includes the reference oscillator, a bias current generator (7), an oscillation detector (6), and an impedance matching unit (3). Following the supply of the bias current (i_vco) after receiving the activation control signal (Sosc), an oscillation detection is performed by the oscillation detector (6), and once oscillation is detected, an additional amplification current (iboost) dependent on the envelope of the detected oscillation, of an amplification current generation circuit is supplied to the reference oscillator (4) in addition to the bias current to amplify the oscillation signal to be above a critical oscillation start threshold so as to precisely define the start time of the oscillator, and enable the oscillation detector (6) to order the stoppage of oscillation of the reference oscillator (4).

A ring oscillator including: an oscillation circuit including an even number of inverters connected in a ring configuration, the oscillation circuit outputting a clock signal; plural potential fixing circuits respectively connected between pairs of the inverters, each of plural potential fixing circuits being switchable between a connected and a disconnected state in response to a first control signal; and an adjustment circuit that adjusts a drive capability of the inverters based on a second control signal, wherein, during startup, the drive capability is controlled to be a first capability, in which the potential fixing circuits are connected, by the first control signal, and wherein, after a predetermined time has elapsed after the first control signal is output, the drive capability is controlled to be a second capability, higher than the first capability, in which the potential fixing circuits are disconnected, by the second control signal.

Embodiments of the present application provide an apparatus for injecting energy into a crystal in a crystal oscillator, and a crystal oscillator. The apparatus includes: a crystal; a voltage-controlled oscillator configured to output an oscillation signal to the crystal; a ramp voltage generating circuit configured to generate a ramp voltage that changes over time; a first switch disposed between the ramp voltage generating circuit and the voltage-controlled oscillator; a first capacitor, where a first terminal of the first capacitor is connected to the first switch and the voltage-controlled oscillator, and a second terminal of the first capacitor is grounded; and a control circuit configured to control a status of the first switch according to a current through the crystal. Therefore, the apparatus can efficiently inject energy into the crystal.

An oscillator circuit has a reconfigurable oscillator amplifier. The reconfigurable oscillator amplifier is used to be coupled to a resonant circuit in parallel. The reconfigurable oscillator amplifier supports different circuit configurations for different operation modes, respectively. The reconfigurable oscillator amplifier has at least one circuit component shared by the different circuit configurations. The reconfigurable oscillator amplifier employs one of the different circuit configurations under one of the different operation modes.

A crystal oscillator circuit is provided. The crystal oscillator circuit includes an oscillator start-up circuit having a first output terminal and a second output terminal, where the second output terminal outputs a first oscillation signal; and a waveform conversion circuit configured to convert the first oscillation signal to a rectangular wave signal. The crystal oscillator circuit also includes a first current source configured to output a first current to drive the oscillator start-up circuit; and a second current source configured to output a second current, and being connected in parallel with the first current source to jointly drive the oscillator start-up circuit. Further the crystal oscillator circuit includes a pulse generation circuit configured to generate a control pulse signal to control the second current source to output the second current after power on and to stop outputting the second current after a preset time.

An oscillator circuit with an oscillator stage and a first current source arranged to drive the oscillator stage is presented. The oscillator stage has an oscillator stage input terminal, an oscillator stage output terminal, an oscillator arranged to provide an oscillating signal between the oscillator stage input terminal and the oscillator stage output terminal. The oscillator circuit has an operational amplifier with an inverting input, a non-inverting input and an operational amplifier output. The oscillator stage input terminal and the oscillator stage output terminal are coupled to the inverting input and non-inverting input. The operational amplifier output is coupled to the oscillator stage input terminal such that the oscillator stage input terminal and the oscillator stage output terminal are controlled to have a same DC voltage level.