US 4,785,443 A · Light control circuit of optical disc system

Abstract

A light control circuit of an optical disc system for controlling light from a light emitting element at a read power level even if a write data operation is performed. The light control circuit includes a light control circuit, a superimposedly energizing circuit for providing a light for data write and a subtraction circuit for subtracting a predetermined current from a light sensing element. A light control circuit may further include a reference value setting circuit for automatically finding and determining reference values of a read power level, a write power level, and a subtraction value. The reference values may be defined with respect to an origin of the characteristic of the light emitting element where a current flowing through the light emitting element is substantially zero. Alternatively, the reference values may be defined with respect to another origin of the characteristic of the light emitting element where a current flowing through the light emitting element is near to a current providing the first predetermined level.

Claims25

Dependent claims

A light control circuit of an optical disc system having an optical disc storing data, a light emitting element used for writing data to and reading data from the optical disc, and a light sensing element sensing light from the light emitting element, comprising:

light control means, operatively connected to the light emitting element and the light sensing element, for energizing the light emitting element and for controlling a light level of the light emitting element at a first predetermined level sufficient for reading data from the optical disc in response to a signal from the light sensing element;
energizing means, operatively connected to the light emitting element and said light control means, for energizing the light emitting element in cooperation with said light control means, at a second predetermined level sufficient for writing data in the optical disc, when data is written to the optical disc;
and
subtracting means, operatively connected to the light sensing element and to said light control means in parallel, being synchronously operable with said energizing means, for subtracting a third predetermined level from the signal from the light sensing element.

1 more element

A method for setting reference values of a light control circuit including a light controlling means for controlling a light level emitted by a light emitting means in accordance with first data and second data, first D/A means operatively connected to the light control means for receiving the first data, light sensing means for sensing a level of light provided by the light emitting means, energizing means operatively connected to the light control means for energizing the light control means in accordance with the second data, second D/A means operatively connected to the energizing means, for providing the second data, subtracting means for subtracting a level of light sensed by the light sensing means and a level of light emitted from the light emitting means, in response to third data, third D/A means, operatively connected to the subtracting means, for providing the third data, said method comprising the following steps:

substantially disabling the light control means;
continuously changing the first data applied to the first D/A converter means until a read level of the light sensing means reaches said a predetermined level and determining a first reference value for said first predetermined level;
energizing the energizing means;
continuously changing the first data applied to the first D/A converter means until a read level of said light sensing means reaches said a predetermined level and determining a first reference value for said first predetermined level;
energizing the energizing means;
continuously changing second data applied to the second D/A converter means until a read level of the light sensing means reaches a second predetermined level and determining a second reference value for said second predetermined level;
continuously changing second data applied to the second D/A converter means until a read level of the light sensing means reaches a second predetermined level and determining a second reference value for said second predetermined level;
energizing the subtracting means and applying said second reference value to the third D/A converter means to provide the third data;
continuously decreasing the third data until a read level of the light sensing means reaches said first predetermined level and determining a third reference value for said third reference level;
and
restoring the operation of the light control means.

8 more elements

A method for setting reference values of a light control circuit, including a light controlling means for controlling a light level emitted by a light emitting means in accordance with first data and second data, first D/A means operatively connected to the light control means for receiving the first data, light sensing means for sensing a level of light provided by the light emitting means, energizing means operatively connected to the light control means for energizing the light control means in accordance with the second data, second D/A means operatively connected to the energizing means, for providing the second data, subtracting means for subtracting a level of light sensed by the light sensing means and a level of light emitted from the light emitting means, in response to third data, third D/A means, operatively connected to the subtracting means, for providing the third data, said method comprising the following steps of:

substantially disabling said deviation calculation means in said light control means;
continuously changing the first data applied to the first D/A converter means until a read level of the light sensing means reaches said a predetermined level and determining a first reference value for said first predetermined level;
energizing the energizing means;
continuously changing second data applied to the second D/A converter means until a read level of the light sensing means reaches a second predetermined level and determining a second reference value for said second predetermined level;
de-energizing said energizing means and applying said second reference value to the third D/A converter means;
restoring said light control means and energizing said energizaing means;
continuously decreasing the third data until a read level of the light sensing means reaches said first predetermined level and determining a third reference value for said third reference level;
so that said first, said second and said third predetermined levels are provided in accordance with a characteristic of the light emitting element.

5 more elements

Dependencies are inferred from the claim text.

Light control circuit of optical disc system

Life of this patent

Light control circuit of optical disc system

Life of this patent

Abstract

Claims25