Patent ID: 7623839

Claim:
A semiconductor integrated circuit comprising: a mixer circuit which includes a first MOS transistor whose source is connected to a first terminal receiving a first current signal formed by voltage-current converting a radio frequency signal, whose gate receives a first local oscillation signal via a first capacitance, and whose drain is connected to a second terminal which outputs a second current signal with the first local oscillation signal superimposed thereon, and a second MOS transistor whose source is connected to the first terminal, whose gate receives, via a second capacitance, a second local oscillation signal which is an inverted signal of the first local oscillation signal, and whose drain is connected to a third terminal which outputs a third current signal with the second local oscillation signal superimposed thereon; a third MOS transistor whose drain is connected to a first potential, and which has a conductivity type and a threshold value which are the same as those of the first MOS transistor and the second MOS transistor; a current source connected between the source of the third MOS transistor and a second potential; a voltage dividing circuit which is connected between the first potential and the second potential, and divides a voltage between the first potential and the second potential to output the divided voltage as a reference voltage; and a differential amplifier circuit whose in-phase input receives the reference voltage, whose anti-phase input receives the source potential of the third MOS transistor, and whose output is connected to the gate of the third MOS transistor, wherein the output voltage of the differential amplifier circuit is applied to the gate of the first MOS transistor via a first resistor, and to the gate of the second MOS transistor via a second resistor, and wherein DC voltages of the drain and the source of the first and second MOS transistors are controlled to be equal to the reference voltage.