Synopsys, Inc.

Jasjeet Singh

Dino Anthony Toffolon

John Theodore Stonick

Jianping Wen

Daniel Keith Weinlader

David Andrew Yokoyama-Martin

Skye Wolfer

James P Flynn

Richard H Steeves

Nacer Eddine Belabbes

One embodiment of the present invention provides a phase-locked loop (PLL) for synthesizing a fractional frequency. The PLL can include a 1/N frequency divider, a voltage-controlled oscillator (VCO), a programmable phase mixer, and a phase detector. The programmable phase mixer can be coupled between an output of the VCO and an input of the frequency divider, wherein the programmable phase mixer is configured to receive the output clock signal from the VCO and generate a first clock signal of frequency fby varying a phase of the output clock signal. The frequency divider is configured to receive the first clock signal from the programmable phase mixer and generate a second clock signal of frequency f=f/N. The phase detector can receive a reference clock signal and the second clock signal as inputs, and the phase detector's output can be used to generate the control voltage for the VCO.

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Embodiments of the present invention provide a system for controlling a startup time of an oscillator circuit. The system includes a variable current source coupled to the oscillator circuit, wherein a startup time of the oscillator circuit is proportional to a bias current input into the oscillator circuit from the variable current source. The system also includes a control mechanism coupled to the variable current source and to the output of the oscillator circuit. Upon startup, the control mechanism is configured to adjust the variable current source to input a large startup bias current into the oscillator circuit. After the oscillator circuit outputs a predetermined number of oscillations during startup, the control mechanism is configured to adjust the variable current source to decrease its current to a smaller steady-state bias current into the oscillator circuit.

Low-power fast-startup oscillator with digital feedback control

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Brampton, Canada

Jasjeet Singh