US 2010/0134157 A1Published application

PLL circuit and method of cotrolling the same

AssigneeNEC Electronics Corporation

InventorToshitsugu Kawashima

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Abstract

A PLL circuit according to an exemplary aspect of the present invention includes: a PFD that detects a phase difference between two clock signals; an LPF that outputs a voltage based on a detection result of the PFD; a VCO that controls a frequency of a VCO output clock output based on the voltage; a frequency divider that divides a frequency of the VCO output clock and outputs an output clock; and an automatic adjustment circuit that adjusts a frequency division ratio of the frequency divider based on the voltage. The automatic adjustment circuit includes a comparison circuit that outputs a control signal for controlling the frequency divider and a control signal for controlling the reference voltage. This circuit configuration makes it possible to control an oscillation frequency of a PLL circuit with accuracy and stability.

Claims13

Dependent claims

A PLL circuit comprising:

a phase frequency detector that detects a phase difference between a reference signal and a feedback signal;
a filter circuit that outputs a control voltage based on an output signal from the phase frequency detector;
a voltage control oscillation circuit that controls a frequency of a clock signal output based on the control voltage;
a frequency dividing circuit that divides the frequency of the clock signal and outputs the feedback signal;
and
an automatic adjustment circuit that adjusts a frequency division ratio of the frequency dividing circuit based on the control voltage,
wherein the automatic adjustment circuit comprises:
a comparison circuit that outputs a first control signal for controlling the frequency division ratio based on a potential difference between the control voltage and a first reference voltage, and outputs a second control signal for controlling the first reference voltage based on the potential difference between the control voltage and the first reference voltage;
and
a reference voltage selection circuit that selects the first reference voltage based on the second control signal and outputs the first reference voltage selected.

7 more elements

Dependencies are inferred from the claim text.