An FM modulator measuring an f-V characteristic of a voltage controlled oscillator in a reduced time period. In the FM modular a characteristic measurement time control section 110 notifies a correction section 108 of a time at which a measurement of the f-V characteristic of a voltage controlled oscillator 103 is to start and a time at which the measurement of the f-V characteristic of the voltage controlled oscillator 103 is to and while a carrier wave frequency is being changed to a predetermined frequency. Thus, the correction section 108 measures the f-V characteristic of the voltage controlled oscillator 103 in a reduced time period.
1. An FM modulator for FM-modulating a signal containing a modulation component and outputting, as an output signal, a signal having been FM-modulated, comprising:
a reference signal generator for generating a reference signal;
a voltage controlled oscillator for outputting, as the output signal, a signal in accordance with a control voltage being applied thereto; and
a control circuit for converging, to a predetermined frequency, an oscillation frequency of the voltage controlled oscillator using the reference signal, and, after the oscillation frequency has been converged to the predetermined frequency, changing, in accordance with the signal containing the modulation component, the control voltage to be applied to the voltage controlled oscillator, and causing the voltage controlled oscillator to output the output signal having been FM-modulated, wherein
the control circuit includes a correction section for measuring, using the oscillation frequency of the voltage controlled oscillator and the control voltage to be applied to the voltage controlled oscillator, an f-V characteristic representing a relationship between the oscillation frequency and the control voltage, and applying, to the voltage controlled oscillator, the control voltage having been corrected in accordance with the f-V characteristic having been measured,
the correction section measures the f-V characteristic while the oscillation frequency is being converged to the predetermined frequency, and applies, to the voltage controlled oscillator, the control voltage having been corrected in accordance with the f-V characteristic having been measured such that the voltage controlled oscillator outputs a signal equivalent to a signal outputted by a voltage controlled oscillator having a linear f-V characteristic, and
the FM modulator further comprises a characteristic measurement time control section for notifying the correction section of a time at which the f-V characteristic is to be measured.
2. The FM modulator according to claim 1 , wherein the control circuit converges the oscillation frequency to the predetermined frequency by performing a digital process.
3. The FM modulator according to claim 1 , wherein the control circuit converges the oscillation frequency to the predetermined frequency by performing an analog process.
4. The FM modulator according to claim 1 , wherein
a phase locked loop circuit, including the control circuit and the voltage controlled oscillator, performs a process of converging the oscillation frequency to the predetermined frequency utilizing a first time period and a second time period,
the first time period represents a time period from a start of the process to a time at which the oscillation frequency reaches a predetermined frequency range including the predetermined frequency,
the second time period represents a time period from the time at which the oscillation frequency reaches the predetermined frequency range including the predetermined frequency to a time at which the oscillation frequency is locked, and
the correction section measures the f-V characteristic in an arbitrary time period included in the first time period.
5. The FM modulator according to claim 4 wherein the correction section starts measuring the f-V characteristic at a beginning of the first time period, and ends measuring the f-V characteristic at an end of the first time period.
6. The FM modulator according to claim 4 , wherein
a phase of the oscillation frequency is repeatedly inverted in the first time period using the predetermined frequency as a reference until the oscillation frequency reaches the predetermined frequency range, and
the correction section measures the f-V characteristic from an inflection point of the oscillation frequency to an immediately following inflection point of the oscillation frequency.
7. The FM modulator according to claim 4 , wherein
a phase of the oscillation frequency is repeatedly inverted in the first time period using the predetermined frequency as a reference until the oscillation frequency reaches the predetermined frequency range, and
the correction section measures the f-V characteristic from a time at which the phase of the oscillation frequency is inverted to a time at which the phase of the oscillation frequency is inverted for a second time after the time at which the phase of the oscillation frequency is inverted.
8. The FM modulator according to claim 1 , wherein
a phase locked loop circuit, including the control circuit and the voltage controlled oscillator, performs a process of converging the oscillation frequency to the predetermined frequency utilizing a first time period and a second time period,
the first time period represents a time period from a start of the process to a time at which the oscillation frequency reaches a predetermined frequency range including the predetermined frequency,
the second time period represents a time period from the time at which the oscillation frequency reaches the predetermined frequency range including the predetermined frequency to a time at which the oscillation frequency is locked, and
the correction section measures, in an arbitrary time period included in the second time period, the f-V characteristic necessary for performing an FM-modulation using the predetermined frequency by changing the control voltage to be applied to the voltage controlled oscillator.
9. The FM modulator according to claim 8 wherein the correction section staffs to measure the f-V characteristic at a beginning of the second time period, and, when the f-V characteristic necessary for performing the FM modulation using the predetermined frequency has been measured, stops correcting the control voltage.
10. The FM modulator according to claim 1 , wherein the correction section measures the f-V characteristic after a channel outputted by the voltage controlled oscillator is changed.
11. The FM modulator according to claim 1 , wherein the correction section measures the f-V characteristic after the FM modulator has been powered on.
12. A wireless device for transmitting an FM-modulated radio signal, comprising an FM modulator for FM-modulating a signal containing a modulation component and outputting, as an output signal, a signal having been FM-modulated,
wherein the FM-modulator includes:
a reference signal generator for generating a reference signal;
a voltage controlled oscillator for outputting, as the output signal, a signal in accordance with a control voltage being applied thereto; and
a control circuit for converging, to a predetermined frequency, an oscillation frequency of the voltage controlled oscillator using the reference signal, and, after the oscillation frequency has been converged to the predetermined frequency, changing, in accordance with the signal containing the modulation component, the control voltage to be applied to the voltage controlled oscillator, and causing the voltage controlled oscillator to output the output signal having been FM-modulated
wherein the control circuit includes a correction section for measuring, using the oscillation frequency of the voltage controlled oscillator and the control voltage to be applied to the voltage controlled oscillator, an f-V characteristic representing a relationship between the oscillation frequency and the control voltage, and applying, to the voltage controlled oscillator, the control voltage having been corrected in accordance with the f-V characteristic having been measured,
wherein the correction section measures the f-V characteristic while the oscillation frequency is being converged to the predetermined frequency, and applies, to the voltage controlled oscillator, the control voltage having been corrected in accordance with the f-V characteristic having been measured such that the voltage controlled oscillator outputs a signal equivalent to a signal outputted by a voltage controlled oscillator having a linear f-V characteristic, and
wherein the FM modulator further comprises a characteristic measurement time control section for notifying the correction section of a time at which the f-V characteristic is to be measured.