A technique for reducing noise in an output clock signal of a feedback control system (e.g., a PLL or FLL) samples rising edge errors and falling edge errors between a reference clock signal and a feedback clock signal. The technique applies edge alignment correction to reduce or eliminate edge alignment errors between the reference clock signal and the feedback clock signal. A PLL generates an output clock signal based on a control signal generated using an error signal generated based on a rising edge difference between a rising edge of an input clock signal and a corresponding edge of an edge alignment corrected feedback clock signal and based on a falling edge difference between a falling edge of the input clock signal and a corresponding edge of the edge alignment corrected feedback clock signal. The edge alignment corrected feedback clock signal is partially based on the output clock signal.

A technique for reducing noise in an output clock signal of a feedback control system (e.g., a PLL or FLL) samples rising edge errors and falling edge errors between a reference clock signal and a feedback clock signal. The technique applies edge alignment correction to reduce or eliminate edge alignment errors between the reference clock signal and the feedback clock signal. A PLL generates an output clock signal based on a control signal generated using an error signal generated based on a rising edge difference between a rising edge of an input clock signal and a corresponding edge of an edge alignment corrected feedback clock signal and based on a falling edge difference between a falling edge of the input clock signal and a corresponding edge of the edge alignment corrected feedback clock signal. The edge alignment corrected feedback clock signal is partially based on the output clock signal.

Apparatus and methods for tuning a voltage controlled oscillator (VCO) are provided. In one aspect, a method of auto-tuning in a phase-locked loop includes generating a VCO clock signal using a VCO coupled to a capacitor array, dividing the VCO clock signal to generate a divided clock signal using a prescaler circuit having a selectable division ratio, controlling a value of the selectable division ratio using a first counter and a second counter of a counter module, generating a phase-frequency detector feedback signal based on a division control signal M and the divided clock signal using the counter module, counting a number of cycles of the divided clock signal that occur during a calibration interval using a cycle counter of a digital processing logic circuit, and determining the value of a capacitor array control signal based on the number of cycles counted during the calibration interval.

Apparatus and methods for tuning a voltage controlled oscillator (VCO) are provided. In one aspect, a method of auto-tuning in a phase-locked loop includes generating a VCO clock signal using a VCO coupled to a capacitor array, dividing the VCO clock signal to generate a divided clock signal using a prescaler circuit having a selectable division ratio, controlling a value of the selectable division ratio using a first counter and a second counter of a counter module, generating a phase-frequency detector feedback signal based on a division control signal M and the divided clock signal using the counter module, counting a number of cycles of the divided clock signal that occur during a calibration interval using a cycle counter of a digital processing logic circuit, and determining the value of a capacitor array control signal based on the number of cycles counted during the calibration interval.

A tuning array selection circuit, together with a decoder and a voltage controlled oscillator (VCO), can be employed to overcome some disadvantages of previous methods of phase locked loops. For example, a VCO can include a coarse tuning array and a fine tuning array. A coarse tuning array can be used to tune a VCO to generate a signal within a wide frequency range. A fine tuning array can be used to tune a VCO to generate a signal within a narrow frequency range. In one embodiment, the narrow frequency range is within the wide frequency range. The tuning array selection circuit can coordinate selection of appropriate fine tuning devices and narrow tuning devices to reduce transition jitter and the risk of fail locking of phase locked loops.

A tuning array selection circuit, together with a decoder and a voltage controlled oscillator (VCO), can be employed to overcome some disadvantages of previous methods of phase locked loops. For example, a VCO can include a coarse tuning array and a fine tuning array. A coarse tuning array can be used to tune a VCO to generate a signal within a wide frequency range. A fine tuning array can be used to tune a VCO to generate a signal within a narrow frequency range. In one embodiment, the narrow frequency range is within the wide frequency range. The tuning array selection circuit can coordinate selection of appropriate fine tuning devices and narrow tuning devices to reduce transition jitter and the risk of fail locking of phase locked loops.

A tuning array selection circuit, together with a decoder and a voltage controlled oscillator (VCO), can be employed to overcome some disadvantages of previous methods of phase locked loops. For example, a VCO can include a coarse tuning array and a fine tuning array. A coarse tuning array can be used to tune a VCO to generate a signal within a wide frequency range. A fine tuning array can be used to tune a VCO to generate a signal within a narrow frequency range. In one embodiment, the narrow frequency range is within the wide frequency range. The tuning array selection circuit can coordinate selection of appropriate fine tuning devices and narrow tuning devices to reduce transition jitter and the risk of fail locking of phase locked loops.

A tuning array selection circuit, together with a decoder and a voltage controlled oscillator (VCO), can be employed to overcome some disadvantages of previous methods of phase locked loops. For example, a VCO can include a coarse tuning array and a fine tuning array. A coarse tuning array can be used to tune a VCO to generate a signal within a wide frequency range. A fine tuning array can be used to tune a VCO to generate a signal within a narrow frequency range. In one embodiment, the narrow frequency range is within the wide frequency range. The tuning array selection circuit can coordinate selection of appropriate fine tuning devices and narrow tuning devices to reduce transition jitter and the risk of fail locking of phase locked loops.

A method for enforcing phase coherency in a self-synchronizing system with multiple frequency dividers includes synchronizing an asynchronous reset to a first output of a first divider to generate a global reset, wherein the first output is generated by dividing a Voltage Controlled Oscillator (VCO) output of a VCO into a plurality of phases including a common phase. The global reset is applied to each of at least a second divider and a third divider to temporally align the first output during the common phase with a second output of the second divider and a third output of the third divider, wherein the second output and the third output are generated by dividing the VCO output by the respective second divider and the third divider, and applying the global reset enables a respective state transition on the second output and the third output beginning during the common phase.

A method for enforcing phase coherency in a self-synchronizing system with multiple frequency dividers includes synchronizing an asynchronous reset to a first output of a first divider to generate a global reset, wherein the first output is generated by dividing a Voltage Controlled Oscillator (VCO) output of a VCO into a plurality of phases including a common phase. The global reset is applied to each of at least a second divider and a third divider to temporally align the first output during the common phase with a second output of the second divider and a third output of the third divider, wherein the second output and the third output are generated by dividing the VCO output by the respective second divider and the third divider, and applying the global reset enables a respective state transition on the second output and the third output beginning during the common phase.