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US 8,134,392 B2Granted
Phase locked loop
AssigneeRenesas Electronics Corporation
InventorTakashi Kawamoto
Life of this patent
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Abstract
A phase locked loop (PLL) which has a desired frequency characteristic even though a manufacturing process of a semiconductor integrated circuit has fluctuations. The semiconductor integrated circuit includes the PLL and a control unit. The PLL has a phase frequency detector, a loop filter, a voltage controlled oscillator (VCO) and a divider. The VCO comprises a voltage-current converter (VIC) and a ring oscillator. In response to a control voltage, the VIC generates a control current for setting each operating current of the ring oscillator. The control unit switches the PLL to a calibration operating period of its open loop and a normal operating period of its closed loop.
Claims8
A semiconductor integrated circuit comprising:
- a phase locked loop;
- and
- a control unit,
- wherein the phase locked loop comprises a phase frequency detector, a loop filter, a voltage controlled oscillator and a divider,
- wherein a reference signal and a feedback signal from an output of the divider are respectively capable of being supplied to one input terminal of the phase frequency detector and another input terminal thereof,
- wherein an output of the phase frequency detector is supplied to a control input of the voltage controlled oscillator via the loop filter, an oscillation output signal of an output of the voltage controlled oscillator is supplied to an input of the divider, and a frequency of the oscillation output signal of the voltage controlled oscillator is capable of being controlled in response to a control voltage supplied to the control input,
- wherein the voltage controlled oscillator comprises a voltage-current converter and a ring oscillator,
- wherein the ring oscillator comprises delays of odd-numbered stages,
- wherein the voltage-current converter generates a control current in response to the control voltage to thereby set each of operating currents of the delays of the ring oscillator by the control current,
- wherein the control unit is capable of switching the phase locked loop to a calibration operating period and a normal operating period,
- wherein during the normal operating period, the phase locked loop is controlled to a closed loop by the control unit, whereas during the calibration operating period, the phase locked loop is controlled to an open loop by the control unit,
- wherein during the normal operating period, the output of the phase frequency detector is supplied via the loop filter to the control input of the voltage controlled oscillator as the control voltage of a predetermined level at the phase locked loop controlled to the closed loop to thereby bring the frequency of the oscillation output signal of the voltage controlled oscillator to a predetermined frequency determined by the frequency of the reference signal and a division ratio of the divider,
- wherein during the calibration operating period, the measurement of the frequency of the oscillation output signal of the voltage controlled oscillator in a state in which a reference voltage approximately equal in level to the control voltage of the predetermined level is being supplied to the control input of the voltage controlled oscillator at the phase locked loop controlled to the open loop, is executed by the control unit, and
- wherein the control unit sets a value of a first operation parameter of the voltage-current converter of the voltage controlled oscillator in such a manner that the frequency of the oscillation output signal of the voltage controlled oscillator in the state in which the reference voltage is being supplied to the voltage controlled oscillator becomes approximately equal to the predetermined frequency during the execution of the measurement of the frequency,
- wherein the phase locked loop further comprises a selector controlled by the control unit, and
- wherein the selector selects the control voltage of the predetermined level during the normal operating period, and the selector selects the reference voltage during the calibration operating period and supplies the selected voltage to the control input of the voltage controlled oscillator,
- wherein prior to the setting of the value of the first operation parameter of the voltage-current converter, the measurement of the frequency of the oscillation output signal of the voltage controlled oscillator in a state in which the control voltage having a level of a ground potential is being supplied to the control input of the voltage controlled oscillator of the phase locked loop controlled to the open loop is executed by the control unit during the calibration operating period, and
- wherein during the calibration operating period, the control unit sets a value of a second operation parameter of the voltage-current converter of the voltage controlled oscillator, prior to the setting of the value of the first operation parameter of the voltage-current converter in such a manner that the frequency of the oscillation output signal in the state in which the control voltage having the level of the ground potential is being supplied to the voltage controlled oscillator becomes approximately equal to a predetermined offset frequency during the execution of the measurement.
15 more elements
Dependencies are inferred from the claim text.