| 摘要 |
<p>A light control circuit of an optical disc system controls the light intensity from a laser diode (LD) at a read power level even if a write data operation is performed. The light control circuit comprises a light controller (2, 3, 5) which energises the laser diode and controls its light output at a predetermined level sufficient for reading data from the optical disc in response to a signal from a photodiode (PD). A transistor circuit (6, 8) superimposes energisation of the laser diode in addition to the energisation by the light controller, at a second predetermined level sufficient for writing data to the optical disc. A subtracting circuit (9, 10), operable synchronously with the superimposed energisation circuit, subtracts a third predetermined level, corresponding to the electrical power supplied by the superimposed energisation circuit to the laser diode, from the signal of the photodiode. The circuit may also include a reference value setting circuit (21, 4, 16, 7, 14) for automatically finding and determining reference values of a read power level, a write power level and a subtraction value.</p> |
