Temperature invariant, magneto-optic modulator coil driving circuit

A magnetic modulator coil driving circuit, for use in a magneto-optical recording system including laser light means and magnetic biasing means, having a first coil and a second coil, for generating and directing a light beam and a magnetic field, respectively, to a magneto-optical recording medium which is divided into data sectors, each sector having a trial writing area at the beginning of the sector on which a trial data are written during a trial writing period, comprising:

• means for supplying electrical currents;
• a series connection of a first switching means and a first resistor connected in series with the means for supplying electrical currents and the first coil, the first switching means being provided with a first control terminal;
• a series connection of a second switching means and a second resistor connected in series with the means for supplying electrical currents and the second coil, the second switching means being provided with a second control terminal;
• first bias voltage setting circuit means which includes a first comparator for comparing a voltage drop across the first resistor with a reference voltage, a first sample and hold circuit for sampling and holding an output of the first comparator, and a first buffer amplifier for receiving an output of the first sample and hold circuit and supplying an amplified output signal to the control terminal of the first switching means;
• second bias voltage setting circuit means which includes a second comparator for comparing a voltage drop across the second resistor with a reference voltage, a second sample and hold circuit for sampling and holding an output of the second comparator, and a second buffer amplifier for receiving an output of the second sample and hold circuit and supplying an amplified output signal to the control terminal of the second switching means;
• a data input circuit for supplying modulating data signals to the first control terminal and the second control terminal to turn on and off, alternately, the first and second switching means;
• and
• control means for supplying, during the writing of trial data in a trial writing area of a given sector on the magneto-optic disk, the reference voltage to the first comparator and the second comparator, supplying modulating data signals corresponding to the trial data to the data input circuit, and supplying a control signal to the first sample and hold circuit and the second sample and hold circuit to cause the first sample and hold circuit and the second sample and hold circuit to sample and hold the outputs of the first and second comparators, respectively, during the writing of trial data in the trial writing area of the given sector and to thereafter supply the sampled and held outputs of the first comparator and the second comparator as inputs to the first buffer amplifier and the second buffer amplifier, respectively, during a time when data is being recorded in the given data sector.