ADJUSTING METHOD FOR FOCUS BIAS SIGNAL IN OPTICAL DISK REPRODUCING DEVICE

PURPOSE:To quantitatively and quickly adjust a focus bias signal to an optimum point by setting a bias signal of a focus circuit between prescribed first and second average values. CONSTITUTION:A clock whose synchronization is larger than that of a reproducing output RF by an optical pickup from an oscillating circuit 30 passing through a level converting circuit 31 is supplied to an adder 29 of a focus servo- circuit 12, and the left and the right minimum values, respectively of a convex curve to an optimum bias value of a waveform of the output RF are held in minimum value holding circuits 33, 34 through switches 36, 38 controlled by a clock passing through an inverter 32. When a variable resistance 14A of the circuit 12 is adjusted so that a difference of these holding values becomes '0' by a subtracting circuit 39, a bias is controlled to an optimum point of an average value of both the holding values. In the same way, an optimum point of an average value against the jitter quantity is determined, and focus bias point is brought to optimum control easily and quantitatively without executing a visual observation of a reproducing waveform from a middle point of both the optimum points.