To reduce phase noise not only when a MOS transistor which constitutes an inverter cell operates in a saturated region but also in a linear region.
A voltage-controlled oscillator comprises a ring oscillator and a dummy inverter 110. The ring oscillator includes inverter cells 100 connected in a circular pattern. Each inverter cell 100 comprises: an operational amplifier 120 which outputs an amplified signal obtained by amplifying a potential difference between a signal from a dummy inverter cell 110 and a reference signal; a first MOS transistor 101 which is connected to a second MOS transistor 102 and receives the amplified signal; a second MOS transistor 102 and a third MOS transistor 103 serving as an inverter input portion and an inverter output portion, respectively; and a fourth MOS transistor 104 which is connected to the third MOS transistor 103 and receives a control signal for controlling the frequency of an oscillation signal. The dummy inverter 110 has the same structure as the inverter cells 100 and has its inverter output portion short-circuited to its inverter input portion.
Satoshi Kono
Makoto Nakamura
Kurata Masatoshi
Takashi Mine
Yoshihiro Fukuhara
Sadao Muramatsu
Ryo Hashimoto