Systems and methods with reduced reference spurs using a crystal oscillator for broadband communications
AssigneeNXP B.V.
InventorsRay Rosik, Weinan Gao, Mats Lindstrom
Life of this patent
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Abstract
Systems and methods are provided. In this regard, a representative system incorporates a crystal oscillator circuit and a digital automatic level control circuit. The digital automatic level control circuit is operative to: convert an oscillation amplitude of the crystal oscillator circuit to a proportional DC voltage; convert the DC voltage to a corresponding digital code representation; and adjust bias current and oscillator loop gain such that a desired oscillation amplitude is set.
Claims13
A system comprising:
- a crystal oscillator circuit;
- and
- a digital automatic level control circuit operative to:
- convert an oscillation amplitude of the crystal oscillator circuit from a differential output signal to a proportional DC voltage;
- convert the DC voltage to a corresponding digital code representation;
- and adjust bias current and oscillator loop gain such that a desired oscillation amplitude is set, and
- wherein the crystal oscillator circuit comprises a differential crystal oscillator that includes
- first and second NMOSFET transistors with a programmable tail current source electrically connected as a differential pair;
- an RLC tank electrically connected as a load;
- a crystal electrically connected in series mode and operative as a filter with high quality factor;
- and
- a capacitance transformer operative to block DC bias from the crystal and to couple the RLC tank to the crystal.
A system comprising:
- a crystal oscillator circuit comprising:
- means for limiting an oscillation amplitude of the circuit to a programmable level;
- and
- means for providing increased gain at startup such that drive level dependency variation in a crystal of the circuit is compensated;
- means for digital automatic level control comprising:
- means for converting the oscillation amplitude of the crystal oscillator circuit from a differential output signal to a proportional DC voltage.
A method for reducing reference spurs in an output of a crystal oscillator circuit, the method comprising:
- converting an oscillation amplitude of the crystal oscillator circuit from a differential output signal to a proportional DC voltage;
- converting the proportional DC voltage to a corresponding digital code representation;
- adjusting bias current and oscillator loop gain such that a desired oscillation amplitude is set;
- and
- filtering signals of a crystal of a differential crystal oscillator circuit with an RLC tank electrically connected as a load.
Dependencies are inferred from the claim text.