Image reading device for an optical device

Abstract

When an optical disc is set to the motor, the slice level is set to a slice level Sk as a reference slice level and a measured jitter value A (S, S) is produced. The slice level is incremented in steps of a fixed quantity Si (S). Then, a measured jitter value B obtained at the incremented slice level is compared with the previous measured jitter value A (S, S). This sequence of process is repeated, and when the measured jitter value A is smaller than the counter value, it is judged that the jitter changes its quantity varying direction to a decreasing direction. Then, the incrementing operation of the slice level is immediately stopped, and the slice level is decremented in steps of another fixed quantity Sd (<Si). The previous measured jitter value C is compared with a measured jitter value D after the slice level is decremented (Sto S). When the measured jitter value C is smaller than the counter jitter value, it is judged that the slice level detected at that time is an optimum slice level.