Circuit and method for controlling a crystal oscillator
AssigneeSemiconductor Components Industries, LLC
InventorAbdullah Ahmed
Life of this patent
Estimating the term…
Abstract
A crystal oscillator circuit that can be controlled for fast start-up and for efficient operation is disclosed. The control includes adjusting a voltage applied to a body terminal of a transistor in order to control the amplification of the crystal oscillator. The amplification can be increased, relative to a motional resistance of the crystal oscillator, at start-up to reduce a start-up time necessary for oscillation. The amplification can also be decreased in order to maintain oscillation after start-up more efficiently. In some implementations, the transistor for control is a fully depleted silicon on insulator (FDSOI) transistor that accommodates a wide range of body bias voltages.
Claims20
An oscillator circuit, comprising:
- an adjustable current mirror, including a first transistor and a second transistor, wherein a current through the second transistor is an output of the adjustable current mirror, the current through the second transistor controllable by a body bias voltage applied to a body terminal of the second transistor;
- a crystal oscillator coupled to the output of the adjustable current mirror and including an amplifier in a feedback loop with a crystal resonator, the amplifier having a transconductance gain corresponding to the current through the second transistor;
- and
- a body bias circuit, coupled to the crystal oscillator and the adjustable current mirror, the body bias circuit configured to apply the body bias voltage to the body terminal of the second transistor during a start-up period to increase the current through the second transistor.
A method for controlling a crystal oscillator, comprising:
- determining a state of the crystal oscillator;
- adjusting, based on the determined state, a body bias voltage at a body terminal of a transistor of an adjustable current mirror to control a current through the transistor of the adjustable current mirror;
- and
- biasing an amplifier of the crystal oscillator using the current through the transistor of the adjustable current mirror to adjust a transconductance gain of the amplifier based on the state.
A crystal oscillator comprising:
- a crystal resonator in a feedback loop with an amplifier, the amplifier being biased by a circuit including:
- an adjustable current mirror including a transistor configured to provide a first current to the amplifier that is sufficient to start oscillation, the first current sufficient to start oscillation being based on a first voltage applied to a body terminal of the transistor;
- and
- a body bias circuit configured to apply a second voltage to the body terminal of the transistor after oscillation has started, the second voltage configuring the transistor to provide a second current to the amplifier that is sufficient to maintain oscillation, the first current sufficient to start oscillation higher than the second current sufficient to maintain oscillation.
Dependencies are inferred from the claim text.