Patent ID: 7847635

Claim:
A transconductance amplifier which supplies an output current proportional to an input voltage, characterized by comprising: a differential pair which is formed of first and second MOS transistors having a common source, and which operates in a triode region; a third MOS transistor of which a source terminal is connected to a drain terminal of the first MOS transistor, and which operates in a saturation region; a fourth MOS transistor of which a source terminal is connected to a drain terminal of the second MOS transistor, and which operates in the saturation region; a first amplifier of which a negative input terminal is connected to the source terminal of the third MOS transistor and of which an output terminal is connected to a gate terminal of the third MOS transistor; a second amplifier of which negative input terminal is connected to the source terminal of the fourth MOS transistor and of which output terminal is connected to a gate terminal of the fourth MOS transistor; a voltage generator circuit which generates a tuning voltage inputted to positive input terminal voltages of the first and second amplifiers, and a common voltage of first and second voltages inputted to the differential pair so that a difference between the tuning voltage and the common voltage is equal to a constant; and a differential-pair input voltage generator circuit which is supplied with a common voltage, and which generates the first voltage outputted to a gate terminal of the first MOS transistor, and the second voltage outputted to a gate terminal of the second MOS transistor, characterized in that the second voltage is equal to 2×(the common voltage)−(the first voltage), the input voltage is equal to a difference between the first voltage and the second voltage, and the output current is equal to a difference between a first current Ip flowing through the drains and sources of the first and third MOS transistors and a second current In flowing through the drains and sources of the second and fourth MOS transistors.