Optical disc system having current monitoring circuit with improved bias coil assembly and controller for laser driver and method for operating same

A magneto-optical disc system of the type having a laser light source, a magnetomotive field generator for subjecting a magneto-optical storage medium to a magnetic field, and a mechanism for focusing light emitted by the light source onto the medium to effect writing of information thereon, said system comprising:

• a laser driver for energizing the laser light source;
• a bias coil assembly disposed in conjunction with the magnetomotive field generator, said bias coil assembly including a wire coil wrapped around a center bar contained by a bias coil housing, said bias coil assembly being positionable above the storage medium so that the entire medium may be within the magnetic field thereby allowing writing of information to all portions of the medium;
• a bias coil driver switchably connected to said bias coil assembly for supplying an electric current thereto;
• a current monitoring circuit connected to said bias coil driver having an output responsive to said electric current;
• a controller including a microprocessor connected to said output of said current monitoring circuit and connected to said laser driver, said controller thereby enabling said laser driver when said output of said current monitoring circuit exceeds a predetermined magnitude so that information is written onto the medium when the electric current flowing in said bias coil exceeds a threshold wherein said microprocessor samples said output of said current monitoring circuit during an interval when said output of said current monitoring circuit is less than said predetermined magnitude, and predicts a time when said output of said current monitoring circuit exceeds a predetermined magnitude.

An optical disc system of the type having a focusing mechanism and a tracking mechanism, the mechanisms being controlled by a feedback loop, the system further having a laser light source, and a magnetomotive field generator for subjecting a magneto-optical storage medium to a magnetic field, wherein the focusing mechanism focuses light emitted by the light source onto the medium to effect writing of information thereon, said system comprising:

• an electronic circuit for generating a servo error signal, said error signal being communicated in the feedback loop for effecting corrections of said focusing mechanism and said tracking mechanism;
• a laser driver for energizing the laser light source;
• a bias coil assembly disposed in conjunction with the magnetomotive field generator. said bias coil assembly including a wire coil wrapped around a center bar contained by a bias coil housing, said bias coil assembly being positionable above the storage medium so that the entire medium may be within the magnetic field thereby allowing writing of information to all portions of the medium;
• a bias coil driver switchably connected to said bias coil assembly for supplying an electric current thereto;
• a current monitoring circuit connected to said bias coil driver having an output responsive to said electric current;
• a controller connected to said output of said current monitoring circuit and connected to said laser driver said controller thereby enabling said laser driver when said output of said current monitoring circuit exceeds a predetermined magnitude so that information processed through said focusing mechanism is written onto the medium when the electric current flowing in said bias coil exceeds a threshold wherein said current monitoring circuit includes a resistor divider, and an analog-to-digital convertor coupled to said divider.

A method for writing information onto a magneto-optical storage medium, said method comprising the steps of:

• providing a magnetomotive field generator for subjecting a region of space to a magnetic field, said generator being responsive to an electric current flowing therethrough and including a bias coil assembly disposed in conjunction with the magnetomotive field generator, said bias coil assembly including a wire coil wrapped around a center bar contained by a bias coil housing, said bias coil assembly being positionable above the storage medium so that the entire medium may be within the magnetic field thereby allowing writing of information to all portions of the medium;
• disposing a magneto-optical storage medium in said region of space;
• conducting said electric current through said generator;
• monitoring a magnitude of the conducted electric current;
• and
• impinging radiant energy on the storage medium for writing information thereon when the monitored magnitude exceeds a predetermined level wherein said step of monitoring is performed by sampling during a ramp-up of said current, and further includes predicting a time at which said predetermined level will be exceeded.

A magneto-optical disc system of the type having a laser light source, a magnetomotive field generator for subjecting a magneto-optical storage medium to a magnetic field, and a mechanism for focusing light emitted by the light source onto the medium to effect writing of information thereon, said system comprising:

• a laser driver for energizing the laser light source;
• a bias coil assembly disposed in conjunction with the magnetomotive field generator, said bias coil assembly including a wire coil wrapped around a center bar contained by a bias coil housing, said bias coil assembly being positionable above the storage medium so that the entire medium may be within the magnetic field thereby allowing writing of information to all portions of the medium;
• a bias coil driver switchably connected to said bias coil assembly for supplying an electric current thereto;
• a current monitoring circuit connected to said bias coil driver having an output responsive to said electric current;
• a controller connected to said output of said current monitoring circuit and connected to said laser driver, said controller thereby enabling said laser driver when said output of said current monitoring circuit exceeds a predetermined magnitude so that information is written onto the medium when the electric current flowing in said bias coil exceeds a threshold wherein an approximate current over voltage transfer function for said bias coil assembly is:
• I ⁢ ( s ) V ⁢ ( s ) = s ⁢ ⁢ τ 2 ⁢ ( s ) + 1 s 2 ⁢ τ 1 ⁢ τ 2 ⁢ ( s ) ⁢ ( 1 - ⁢ ∝ 2 ) + s ⁡ [ τ 1 + τ 2 ⁢ ( s ) ] + 1
• where
• τ1≈1.6 m s;
• τ2(s)≈56(1−i)μs at 100 Hz≈17(1−i)μs at 1000 Hz;
• and
• α≈0.99
• so that said microprocessor may mathematically calculate a time t1 when the electric current flowing in said bias coil exceeds said threshold.

A magneto-optical disc system of the type having a laser light source, a magnetomotive field generator for subjecting a magneto-optical storage medium to a magnetic field, and a mechanism for focusing light emitted by the light source onto the medium to effect writing of information thereon, said system comprising:

• a laser driver for energizing the laser light source;
• a bias coil assembly disposed in conjunction with the magnetomotive field generator, said bias coil assembly including a wire coil wrapped around a center bar contained by a bias coil housing, said bias coil assembly being positionable above the storage medium so that the entire medium may be within the magnetic field thereby allowing writing of information to all portions of the medium;
• a bias coil driver switchably connected to said bias coil assembly for supplying an electric current thereto;
• a current monitoring circuit connected to said bias coil driver having an output responsive to said electric current;
• a controller connected to said output of said current monitoring circuit and connected to said laser driver, said controller thereby enabling said laser driver when said output of said current monitoring circuit exceeds a predetermined magnitude so that information is written onto the medium when the electric current flowing in said bias coil exceeds a threshold wherein said current monitoring circuit includes a resistor divider, and an analog-to-digital convertor coupled to said divider.

An optical disc system for writing information onto a storage medium, the system being of the type having a focusing mechanism and a tracking mechanism, wherein the mechanisms are controlled by a feedback loop, said system comprising:

• an electronic circuit for generating a servo error signal;
• a laser light source;
• a laser driver for energizing the laser light source;
• a magnetomotive field generator for subjecting the medium to a magnetic field;
• a bias coil assembly disposed in conjunction with said magnetomotive field generator, said bias coil assembly including a wire coil wrapped around a center bar contained by a bias coil housing, said bias coil assembly being positionable above the storage medium so that the entire medium may be within the magnetic field thereby allowing writing of information to all portions of the medium;
• a bias coil driver switchably connected to said bias coil assembly for supplying an electric current thereto;
• a current monitoring circuit connected to said bias coil driver having an output responsive to said electric current;
• a controller connected to said output of said current monitoring circuit and connected to said laser driver, said controller enabling said laser driver when said output of said current monitoring circuit exceeds a predetermined magnitude so that information is written onto the medium when the magnetic field coil exceeds a predetermined threshold wherein an approximate current over voltage transfer function for said bias coil assembly is:
• I ⁢ ( s ) V ⁢ ( s ) = s ⁢ ⁢ τ 2 ⁢ ( s ) + 1 s 2 ⁢ τ 1 ⁢ τ 2 ⁢ ( s ) ⁢ ( 1 - ⁢ ∝ 2 ) + s ⁡ [ τ 1 + τ 2 ⁢ ( s ) ] + 1
• where
• τ1≈1.6 m s;
• τ2(s)≈56(1−i)μs at 100 Hz≈17(1−i)μs at 1000 Hz;
• and
• α≈0.99
• so that said microprocessor may mathematically calculate a time t1 when the electric current flowing in said bias coil exceeds said threshold.