A crystal oscillator control circuit includes a first terminal and a second terminal, a current source, and a peak detection and bias voltage adjustment circuit. The first terminal and the second terminal are arranged to couple the crystal oscillator control circuit to a crystal. The current source is coupled to a power supply voltage and generates a bias current. The peak detection and bias voltage adjustment circuit is coupled between the bias current and a ground voltage and coupled to the first terminal, and performs peak detection and bias voltage adjustment to correspondingly generate a first signal at a node. The low-pass filter low-pass filters the first signal to generate a filtered signal. The feedback control circuit is arranged to perform feedback control according to the filtered signal to generate an oscillation signal at one or both of the first terminal and the second terminal.

An oscillator, including a resonance circuit, a cross coupled current source circuit, and a positive feedback circuit coupled between the current source circuit and the resonance circuit, where the resonance circuit is configured to generate a differential oscillation signal having a first oscillation frequency, the positive feedback circuit is configured to receive the differential oscillation signal, and amplify a gain of the differential oscillation signal to obtain a differential output oscillation signal, and the current source circuit is configured to provide an adjustable bias current for the resonance circuit and the positive feedback circuit. Since, the current source circuit provides the adjustable bias current for the positive feedback circuit and the resonance circuit, and forms a transconductance boosted (Gm-boosted) structure with the positive feedback circuit, the positive feedback circuit can amplify the gain of the received differential oscillation signal to obtain the differential output oscillation signal.

A crystal oscillator control circuit includes a first terminal and a second terminal, a current source, and a peak detection and bias voltage adjustment circuit. The first terminal and the second terminal are arranged to couple the crystal oscillator control circuit to a crystal. The current source is coupled to a power supply voltage and generates a bias current. The peak detection and bias voltage adjustment circuit is coupled between the bias current and a ground voltage and coupled to the first terminal, and performs peak detection and bias voltage adjustment to correspondingly generate a first signal at a node. The low-pass filter low-pass filters the first signal to generate a filtered signal. The feedback control circuit is arranged to perform feedback control according to the filtered signal to generate an oscillation signal at one or both of the first terminal and the second terminal.

A Pierce oscillator is provided with a transconductance amplifier transistor having a DC drain voltage that is regulated to equal a reference voltage independently from a DC gate voltage for the transconductance amplifier transistor.

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.

An oscillator, including a resonance circuit, a cross coupled current source circuit, and a positive feedback circuit coupled between the current source circuit and the resonance circuit, where the resonance circuit is configured to generate a differential oscillation signal having a first oscillation frequency, the positive feedback circuit is configured to receive the differential oscillation signal, and amplify a gain of the differential oscillation signal to obtain a differential output oscillation signal, and the current source circuit is configured to provide an adjustable bias current for the resonance circuit and the positive feedback circuit. Since, the current source circuit provides the adjustable bias current for the positive feedback circuit and the resonance circuit, and forms a transconductance boosted (Gm-boosted) structure with the positive feedback circuit, the positive feedback circuit can amplify the gain of the received differential oscillation signal to obtain the differential output oscillation signal.

A reconfigurable crystal oscillator and a method for reconfiguring a crystal oscillator are provided. The reconfigurable crystal oscillator includes a transconductance circuit, a feedback resistor, a crystal tank, an input-end capacitor and an output-end capacitor. Both of the feedback resistor and the crystal tank are coupled between an input terminal and an output terminal of the transconductance circuit. The input-end capacitor is coupled to the input terminal of the transconductance circuit, and the output-end capacitor is coupled to the output terminal of the transconductance circuit. In particular, the transconductance circuit is configured to provide a transconductance, and when an operation mode of the reconfigurable crystal oscillator is switched, an input-end capacitance of the input-end capacitor and an output-end capacitance of the output-end capacitor are switched, respectively.

A Pierce oscillator is provided with a transconductance amplifier transistor having a DC drain voltage that is regulated to equal a reference voltage independently from a DC gate voltage for the transconductance amplifier transistor.

Transceiver circuitry for coupling a functional circuit to a transmission medium includes a transmit path for coupling between the functional circuit and the transmission medium, a receive path for coupling between the transmission medium and the functional circuit, and clock generation circuitry coupled to at least one of the transmit path and the receive path. The clock generation circuitry includes an oscillator having transconductance circuitry, a capacitance element coupled in parallel with the transconductance circuitry, a plurality of inductors coupled in parallel with the transconductance circuitry and the capacitance element, and with each other, and a current source coupled to the plurality of inductors. The capacitance element may be variable. An even number of inductors are arranged so that half of the inductors generate magnetic flux in a first direction, and half of the inductors generate magnetic flux in a second direction opposite to the first direction.