Oscillator circuit with an inverter amplifier having reduced consumption

An inverter oscillator circuit for delivering an alternating output signal, this inverter oscillator circuit including a parallel arrangement, between an input terminal and an output terminal, of an inverter amplifier means, a resonator and a resistor, first and second load capacitors being respectively connected between said input and output terminals, on the one hand, and a supply potential, on the other hand,

• said inverter amplifier means including a first inverter having a first transconductance value, permanently connected between said input and output terminals, and a second inverter having a second transconductance value,
• this inverter oscillator circuit further including control means for controlling said inverter amplifier means such that it has a so-called start-up transconductance value during a start-up phase and a so-called reduced transconductance value, lower than said start-up transconductance value, in steady state at the end of said start-up phase,
• said control means including switching means arranged to connect said second inverter between said input and output terminals during said start-up phase and for disconnecting said second inverter in steady state at the end of said start-up phase,
• wherein the inverter oscillator circuit further includes an amplitude control loop for smoothing an amplitude decrease in the output signal resulting from the passage of said start-up transconductance value to said reduced transconductance value, said amplitude control loop being connected to said first inverter and controlling the amplitude of said alternating output signal in steady state, and
• wherein said second inverter is selectively connected to or disconnected from said input and output terminals by means of first and second switches connected in series in the supply path of said second inverter,
• said first switch being a p-MOS transistor connected by its drain and source terminals between the source terminal of the p-MOS transistor of said second inverter and said first supply potential,
• said second switch being an n-MOS transistor connected by its drain and source terminals between the source terminal of the n-MOS transistor of said second inverter and said second supply potential.

An inverter oscillator circuit for delivering an alternating output signal, this inverter oscillator circuit including a parallel arrangement, between an input terminal and an output terminal, of an inverter amplifier means, a resonator and a resistor, first and second load capacitors being respectively connected between said input and output terminals, on the one hand, and a supply potential, on the other hand,

• said inverter amplifier means including a first inverter having a first transconductance value, permanently connected between said input and output terminals, and a second inverter having a second transconductance value,
• this inverter oscillator circuit further including control means for controlling said inverter amplifier means such that it has a so-called start-up transconductance value during a start-up phase and a so-called reduced transconductance value, lower than said start-up transconductance value, in steady state at the end of said start-up phase,
• said control means including switching means arranged to connect said second inverter between said input and output terminals during said start-up phase and for disconnecting said second inverter in steady state at the end of said start-up phase,
• wherein the inverter oscillator circuit further includes an amplitude control loop for smoothing an amplitude decrease in the output signal resulting from the passage of said start-up transconductance value to said reduced transconductance value, said amplitude control loop being connected to said first inverter and controlling the amplitude of said alternating output signal in steady state, and
• wherein said inverter oscillator circuit further includes a voltage control circuit for powering at least said first inverter with a reduced supply potential.

An inverter oscillator circuit for delivering an alternating output signal, this inverter oscillator circuit including a parallel arrangement, between an input terminal and an output terminal, of an inverter amplifier means, a resonator and a resistor, first and second load capacitors being respectively connected between said input and output terminals, on the one hand, and a supply potential, on the other hand,

• said inverter amplifier means including a first inverter having a first transconductance value, permanently connected between said input and output terminals, and a second inverter having a second transconductance value,
• this inverter oscillator circuit further including control means for controlling said inverter amplifier means such that it has a so-called start-up transconductance value during a start-up phase and a so-called reduced transconductance value, lower than said start-up transconductance value, in steady state at the end of said start-up phase,
• said control means including switching means arranged to connect said second inverter between said input and output terminals during said start-up phase and for disconnecting said second inverter in steady state at the end of said start-up phase,
• wherein the inverter oscillator circuit further includes an amplitude control loop for smoothing an amplitude decrease in the output signal resulting from the passage of said start-up transconductance value to said reduced transconductance value, said amplitude control loop being connected to said first inverter and controlling the amplitude of said alternating output signal in steady state,
• wherein said resonator is a quartz resonator having at least a fundamental torsional vibration mode, and wherein said start-up transconductance value is determined such that the resonator is set into vibration according to said fundamental torsional vibration mode at least during said start-up phase, and
• wherein said resonator has a single cut angle defined by a rotation at a determined angle about the crystallographic axis X of said quartz, such that said resonator includes at least an undesired fundamental flexural vibration mode at a first frequency and said desired fundamental torsional vibration mode at a second frequency higher than said first frequency,
• said start-up transconductance value being determined such that said resonator is set into vibration according to said desired fundamental torsional vibration mode and not according to said undesired fundamental flexural vibration mode.

An inverter oscillator circuit for delivering an alternating output signal, this inverter oscillator circuit including a parallel arrangement, between an input terminal and an output terminal, of an inverter amplifier means, a resonator and a resistor, first and second load capacitors being respectively connected between said input and output terminals, on the one hand, and a supply potential, on the other hand,

• said resonator being a quartz resonator having a first undesired vibration mode at a first frequency and a second desired vibration mode at a second frequency,
• wherein said inverter oscillator circuit further includes:
• control means for controlling said inverter amplifier means such that it has a so-called start-up transconductance value during a start-up phase and a so-called reduced transconductance value, lower than said start-up transconductance value, in steady state at the end of said start-up phase;
• and
• means for smoothing an amplitude decrease in the output signal resulting from the passage of said start-up transconductance value to said reduced transconductance value,
• said start-up transconductance value being determined such that the resonator is set into vibration according to said second desired vibration mode during said start-up phase, and said reduced transconductance value is determined such that the resonator continues to vibrate according to the second desired vibration mode in steady state.

A method for maintaining the vibrations of a resonator and generating an alternating output signal by means of an inverter oscillator circuit including an inverter amplifier means, this resonator having a first undesired vibration mode at a first frequency and a second desired vibration mode at a second frequency,

• this method including:
• a start-up step consisting in controlling said inverter amplifier means such that it has a so-called start-up transconductance value during said staff-up step, this start-up transconductance value being determined such that said resonator is set into vibration according to the desired vibration mode;
• and
• a switching step consisting in controlling said inverter amplifier means such that it has a so-called reduced transcondctance value lower than said start-up transconductance value as soon as said resonator is in steady state.