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US 8,013,682 B2Granted
Frequency synthesizer and method for controlling same
AssigneeRenesas Electronics Corporation
InventorsWeiliang Hu, Noriaki Matsuno
Life of this patent
Estimating the term…
Abstract
A frequency synthesizer includes compensation variable capacitance diodes 53 and 54 in a voltage-controlled oscillator 5 in addition to a variable capacitance diode 52 whose DC bias voltage is controlled by a control voltage signal 11 generated by a low-pass filter 3. A monitor circuit 8 monitors the control voltage signal 11 and changes the level of control signals 16 and 17 when the voltage of the control voltage signal 11 goes out of a range within which the capacitance of the variable capacitance diode 52 can be easily changed. A time constant circuit 72 supplies a DC bias voltage to the compensation variable capacitance diode for smoothing out the level change of the control signals 16 and 17 into a slow voltage change so that a locked state is not canceled.
Claims14
A frequency synthesizer, comprising:
- a phase comparator circuit that compares the phases of a reference clock and feedback clock;
- a low-pass filter that smoothes an output signal of said phase comparator circuit and generates a control voltage signal;
- a voltage-controlled oscillator that includes a first variable capacitance diode whose DC bias voltage is controlled by said control voltage signal and a compensation variable capacitance diode;
- a feedback circuit that generates said feedback clock from an output signal of said voltage-controlled oscillator;
- a monitor circuit that monitors said control voltage signal, outputs a control signal for said compensation variable capacitance diode, and changes the voltage levels of said control signal upon the voltage level of said control voltage signal being out of a predetermined voltage range;
- a time constant circuit that, upon the voltage level of said control signal changes, supplies a DC bias voltage to said compensation variable capacitance diode, slowing down the voltage change so that a locked state that said frequency synthesizer is in not being canceled;
- and
- a lock detection circuit and a lock cancellation signal output inhibiting circuit that inhibits said lock detection circuit from outputting a lock cancellation signal upon said monitor circuit detecting that said control voltage signal has gone out of said predetermined voltage range.
5 more elements
A frequency synthesizer, comprising:
- a phase comparator circuit that compares the phases of a reference clock and feedback clock;
- a low-pass filter that smoothes an output signal of said phase comparator circuit and generates a control voltage signal;
- a voltage-controlled oscillator that includes a first variable capacitance diode whose DC bias voltage is controlled by said control voltage signal and a plurality of compensation variable capacitance diodes;
- a feedback circuit that generates said feedback clock from an output signal of said voltage-controlled oscillator;
- a monitor circuit that monitors said control voltage signal, outputs a plurality of control signals for said plurality of compensation variable capacitance diodes, and changes the voltage levels of at least one of said plurality of control signals upon the voltage level of said control voltage signal being out of a predetermined voltage range;
- a plurality of time constant circuits that, upon the voltage level of any of said plurality of control signals change, supply a DC bias voltage to corresponding one of said plurality of compensation variable capacitance diodes, slowing down the voltage change so that a locked state that said frequency synthesizer is in not being canceled;
- and
- a lock detection circuit and a lock cancellation signal output inhibiting circuit that inhibits said lock detection circuit from outputting a lock cancellation signal upon said monitor circuit detecting that said control voltage signal has gone out of said predetermined voltage range.
5 more elements
A method for controlling a frequency synthesizer, comprising:
- providing a frequency synthesizer including
- a phase comparator circuit that compares the phases of a reference clock and feedback clock;
- a low-pass filter that smoothes an output signal of said phase comparator circuit and generates a control voltage signal;
- a voltage-controlled oscillator that comprises a first variable capacitance diode whose DC bias voltage is controlled by said control voltage signal, a compensation variable capacitance diode, and another capacitance;
- and
- a feedback circuit that generates said feedback clock from a clock generated by said voltage-controlled oscillator;
- the method further comprising:
- in case where said frequency synthesizer is in a locked state, and
- said control voltage signal is out of a predetermined voltage range, and
- upon it being possible to bring said control voltage signal back within a predetermined voltage range via said phase comparator circuit and said low-pass filter circuit, changing a DC bias voltage of said compensation variable capacitance diode thereby changing an oscillation frequency of said voltage-controlled oscillator, changing the DC bias voltage of said compensation variable capacitance diode slowly so that said locked state is not canceled and said control voltage signal is brought back within a predetermined voltage range;
- and
- upon it being impossible to change the DC bias voltage of said compensation variable capacitance diode so as to bring said control voltage signal back within a predetermined voltage range, changing a capacitance value of said another capacitance and restarting the digital tuning of said voltage-controlled oscillator.
9 more elements
Dependencies are inferred from the claim text.