Optical disc apparatus having automatic gain control circuit of open loop type

An optical disc apparatus for radiating light on an optical disc through an objective lens, said apparatus comprising:

• means for moving the objective lens such that the light traces a track of the optical disc;
• first generating means for generating a tracking error signal, the tracking error signal showing a difference between a position of the light radiated on the optical disc and a position of the track of the optical disc corresponding to an amount of light reflected from the optical disc;
• second generating means for generating a sum signal, the sum signal corresponding to an amount of all light reflected from the optical disc;
• amplifying means for amplifying the tracking error signal by multiplying the tracking error signal generated by the first generating means by the sum signal generated by the second generating means to produce a change of level of the tracking error signal, the change corresponding to a change of the amount of all reflected light, the amplifying means having a multiplier yielding a relationship between an input signal of the multiplier and an output signal of the multiplier according to a curved line of a quadratic function, the level of the amplified tracking error signal from the multiplier changing downward when the level of the sum signal as an input signal of the multiplier changes upward;
• and
• means for activating the moving means in correspondence to the tracking error signal amplified by the amplifying means so that the level of the tracking error signal is reduced.