Abstract: A voltage controlled oscillator includes a loop-shaped transmission line, an active circuit connected to a signal line, and a variable capacitor block connected to the signal line and having a plurality of variable capacitor units. Each variable capacitor unit includes a variable capacitor element, a control terminal for applying a control voltage to the variable capacitor element, and a reference voltage terminal for applying a reference voltage to the variable capacitor element. At least two variable capacitor units receive different reference voltages.

Abstract: A division ratio of a first frequency divider that generates a local signal and a division ratio of a second frequency divider that generates a RF interfering signal are different, and a first frequency synthesizer that generates the local signal and a second frequency synthesizer that generates the RF interfering signal employ an identical reference signal. The second frequency synthesizer that generates the RF interfering signal is not provided with a frequency switching function.

Abstract: A frequency synthesizer includes a VCO (1), measures an oscillation frequency of each of multiple bands with a predetermined voltage (V1) applied to the VCO (1), and stores the measurement result to a storage circuit (11). The synthesizer compares a frequency division ratio from a PLL control circuit (14) with the measured oscillation frequency stored to the storage circuit, and selects one band from VCO (1) based on the comparison result. The synthesizer causes the VCO (1) to oscillate on the selected band with a fixed voltage, and determines a frequency band to be used for phase-locked operation in actual based on an error between the oscillation frequency and a reference frequency.

Abstract: A division ratio of a first frequency divider that generates a local signal and a division ratio of a second frequency divider that generates a RF interfering signal are different, and a first frequency synthesizer that generates the local signal and a second frequency synthesizer that generates the RF interfering signal employ an identical reference signal. The second frequency synthesizer that generates the RF interfering signal is not provided with a frequency switching function.

Abstract: A frequency synthesizer includes a VCO (1), measures an oscillation frequency of each of multiple bands with a predetermined voltage (V1) applied to the VCO (1), and stores the measurement result to a storage circuit (11). The synthesizer compares a frequency division ratio from a PLL control circuit (14) with the measured oscillation frequency stored to the storage circuit, and selects one band from VCO (1) based on the comparison result. The synthesizer causes the VCO (1) to oscillate on the selected band with a fixed voltage, and determines a frequency band to be used for phase-locked operation in actual based on an error between the oscillation frequency and a reference frequency.