Kabushiki Kaisha Toshiba

Hiroyuki Haga

Shinobu Murai

Ryuichi Yamashita

Hiromi Kusakabe

Mitsuru Nagata

Satoshi Osuga

A tracking error balance adjustment circuit, and a current control circuit used for a variable gain RF amplifier automatically controlled to output a signal having a predetermined amplitude. The tracking error balance adjustment circuit comprises two separate gain adjusting circuits, each having variable attenuation circuit having first gm amplifier of variable gm type, a second gm amplifier of variable gm type connected to the variable attenuation circuit, and an output circuit connected to the second gm amplifier, comprising an operational amplifier circuit having feedback resistor, wherein the first and second gm amplifiers are differentially controlled commonly by a control current. The a current control circuit is arranged in a variable gain RF amplifier connected to a head amplifier circuit amplifying an output signal from optical pickup, controlling a current output of the variable gain RF amplifier so that it changes in accordance with different functions in the range where the control voltage input is lower than the reference potential and the range where the control voltage input is higher than the reference potential, with the result that the gain control sensitivity can be set almost equal between the two ranges.

Tracking error balance adjustment circuit and a current control circuit used for an optical disk playback apparatus, and an optical disk playback apparatus including the same

To suppress electromagnetic radiation without exerting any harmful influence upon both S/N ratio and dynamic range, a pulse width modulation circuit includes an integrating circuit for integrating an input signal applied to an input terminal with respect to time, a comparing circuit connected to the integrating circuit and having hysteresis characteristics, a feedback circuit for feeding back the output of the comparing circuit to an input of the integrating circuit, and an amplitude modulation circuit, provided in a loop including the integrating circuit and the comparing circuit, for implementing amplitude modulation to modulate a frequency of the output of the comparing circuit. Further, the output of the comparing circuit can be fed-back to the integrating circuit via an amplitude modulation circuit. Alternatively, the amplitude of the output of the integrating circuit is first modulated by the amplitude modulation circuit, before being applied to the comparing circuit. A dither signal is applied to the amplitude modulation circuit or, alternatively, a signal for maintaining frequency of the pulse modulated signal may be applied.

Pulse width modulation circuit

According to this invention, there is provided a drive circuit for a multi-phase brushless DC motor comprising a rotational position detector for detecting a rotational position of a rotor of the motor, a commutation control device for selecting a drive coil to be conducted from the plurality of drive coils, a drive output circuit for supplying a drive current to the drive coil selected by the commutation control devices, a DC servo control loop for detecting a motor speed on the basis of a counter electromotive voltage by rotating the motor and by supplying the drive current from the drive output circuit to the motor, and generating a comparison output in accordance with a difference between the motor speed detection output level and the reference voltage to output the comparison output to the drive output circuit through the commutation control device, and a control device for detecting whether the drive current of the drive output circuit is a predetermined value or more and for weakening a control force of the DC servo control loop when the drive current is the predetermined value or more.

Drive circuit for multi-phase brushless DC motor including drive current

A thermal shutoff circuit for controlling current to an external circuit in response to changes in the temperature of the shutoff circuit. The thermal shutoff circuit includes a source for supplying a voltage which varies with changes in temperature, and a switch circuit responsive to the temperature variable voltage for interrupting the current to the external circuit when the temperature of the shutoff circuit exceeds a predetermined amount. The switch circuit has a detection transistor having a base connected to the temperature variable voltage source for generating a base current responsive to the temperature variable voltage and a compensation transistor connected in series to the detection transistor for generating an equivalent base current.

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Kamakura, Japan

Hiroyuki Haga