Patent ID: 7031684

Claim:
A variable gain amplifier device controlled by a first gain control signal, comprising: a gain controlled amplifier having a gain and including a differential pair of first and second MOS type transistors configured to operate in a weak inversion region; and a control signal converter configured to convert the first gain control signal into a second gain control signal, and supply the second gain control signal to the gain controlled amplifier to exponentially vary the gain with respect to the first gain control signal, wherein the control signal converter comprises a differential pair of third and fourth MOS type transistors including a common source terminal to which a direct current Io is supplied and configured to operate in the weak inversion region, the third MOS type transistor including a drain terminal and a gate terminal which are connected to each other, a current Io·exp(−b·Vc/V T ) (where, Vc is the first gain control signal, V T is the thermal voltage, and b>0) being applied to the drain terminal of the third MOS type transistor, the fourth MOS type transistor including a gate terminal fixed to a constant direct current level, and a potential difference between the gate terminal of the third MOS type transistor and the gate terminal of the fourth MOS type transistor corresponding to the second gain control signal.