Abstract: The present invention provides a frequency synthesizer that is switchable at a high speed and includes a few unnecessary frequency components in an output frequency signal. In a frequency synthesizer 1, a DDS 2 operates based on a clock signal to generate a reference frequency signal with a predetermined reference frequency, and clock signal supply units 41 and 42 switch the clock signals that have different clock frequencies to supply to the DDS 2. When the clock signals are switched to operate the DDS 2, the storage unit 12 stores a combination of a clock frequency fclk, a reference frequency fc, and a dividing number N in association with an output frequency fVCO of the frequency synthesizer 1 such that a spurious frequency does not exist within a predetermined frequency range and a dividing number of a variable frequency divider 302 disposed on a PLL circuit 3 is minimum. Setting units 11 and 24 read setting items stored in the storage unit 12 to set respective units.

Abstract: The present invention provides a frequency synthesizer that is switchable at a high speed and includes a few unnecessary frequency components in an output frequency signal. In a frequency synthesizer 1, a DDS 2 operates based on a clock signal to generate a reference frequency signal with a predetermined reference frequency, and clock signal supply units 41 and 42 switch the clock signals that have different clock frequencies to supply to the DDS 2. When the clock signals are switched to operate the DDS 2, the storage unit 12 stores a combination of a clock frequency fclk, a reference frequency fc, and a dividing number N in association with an output frequency fVCO of the frequency synthesizer 1 such that a spurious frequency does not exist within a predetermined frequency range and a dividing number of a variable frequency divider 302 disposed on a PLL circuit 3 is minimum. Setting units 11 and 24 read setting items stored in the storage unit 12 to set respective units.

Abstract: To provide, in a frequency synthesizer including: a variable attenuator provided at a subsequent stage of a voltage controlled oscillator; a detector; and a control unit outputting a control voltage for adjusting an attenuation amount of the variable attenuator via a digital/analog converter in accordance with a detection voltage, a technology with which a spurious due to a change in an output of the digital/analog converter can be suppressed. A low-pass filter is provided between an output side of a digital/analog converter and a variable attenuator to cut a frequency component corresponding to an overshoot generated when an output of the digital/analog converter is changed.

Abstract: To provide, in a frequency synthesizer including: a variable attenuator provided at a subsequent stage of a voltage controlled oscillator; a detector; and a control unit outputting a control voltage for adjusting an attenuation amount of the variable attenuator via a digital/analog converter in accordance with a detection voltage, a technology with which a spurious due to a change in an output of the digital/analog converter can be suppressed. A low-pass filter is provided between an output side of a digital/analog converter and a variable attenuator to cut a frequency component corresponding to an overshoot generated when an output of the digital/analog converter is changed.

Abstract: To provide, in a frequency synthesizer including: a variable attenuator provided at a subsequent stage of a voltage controlled oscillator; a detector; and a control unit outputting a control voltage for adjusting an attenuation amount of the variable attenuator via a digital/analog converter in accordance with a detection voltage, a technology with which a spurious due to a change in an output of the digital/analog converter can be suppressed. A low-pass filter is provided between an output side of a digital/analog converter and a variable attenuator to cut a frequency component corresponding to an overshoot generated when an output of the digital/analog converter is changed.

Abstract: To provide, in a frequency synthesizer including: a variable attenuator provided at a subsequent stage of a voltage controlled oscillator; a detector; and a control unit outputting a control voltage for adjusting an attenuation amount of the variable attenuator via a digital/analog converter in accordance with a detection voltage, a technology with which a spurious due to a change in an output of the digital/analog converter can be suppressed. A low-pass filter is provided between an output side of a digital/analog converter and a variable attenuator to cut a frequency component corresponding to an overshoot generated when an output of the digital/analog converter is changed.

Abstract: A low noise voltage-controlled oscillating circuit which can remove a power source noise to improve low frequency noise characteristics is disclosed. A capacitor C11 is provided between a base of a driving transistor Q1 and GND, whereby a low frequency noise input into the base can be removed. As the driving transistor Q1, a transistor having a low hFE is used, whereby the low frequency noise input from a power source can be removed. A coil L3 is provided on the emitter side of an oscillating transistor Q2, whereby broadband frequency characteristics can be obtained to improve phase noise frequency characteristics. On the emitter side of the oscillating transistor Q2, a resonance frequency in a resonant circuit having a capacitor C7 and the coil L3 is set near the center of a VCO oscillation frequency band, whereby it is possible to obtain the oscillation frequency which is not easily influenced by the noise.

Abstract: A low noise voltage-controlled oscillating circuit which can remove a power source noise to improve low frequency noise characteristics is disclosed. A capacitor C11 is provided between a base of a driving transistor Q1 and GND, whereby a low frequency noise input into the base can be removed. As the driving transistor Q1, a transistor having a low hFE is used, whereby the low frequency noise input from a power source can be removed. A coil L3 is provided on the emitter side of an oscillating transistor Q2, whereby broadband frequency characteristics can be obtained to improve phase noise frequency characteristics. On the emitter side of the oscillating transistor Q2, a resonance frequency in a resonant circuit having a capacitor C7 and the coil L3 is set near the center of a VCO oscillation frequency band, whereby it is possible to obtain the oscillation frequency which is not easily influenced by the noise.