| 摘要 |
PURPOSE: An adjusting method for focus bias is provided to adjust focus bias based on focus bias voltage having minimum jitter amount. CONSTITUTION: By a first jitter amount of an RF(Radio Frequency) signal over a reference jitter amount, a first bias voltage is supplied to a focus servo circuit for detecting a second jitter amount of the RF signal(S1-S6). By the second amount between reference and first jitter amounts(S11), a second bias voltage is formed by adding an established voltage to the first bias voltage. The second voltage is supplied to the focus servo circuit to detect a third jitter amount. By the second jitter amount between reference and second jitter amounts, a third bias voltage formed by adding half of the established voltage to the second bias voltage is decided as a focus bias voltage(S16). By the third jitter amount over reference and second jitter amounts, a fourth bias voltage formed by subtracting the half of the established voltage from the second bias voltage is decided as the focus bias voltage.
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