Automatic power control apparatus of an optical disc drive

Abstract: An automatic power control (APC) apparatus for reducing time necessary for stabilizing an APC circuit at the initial stage of automatic power control of a disc drive is provided. The APC circuit is designed such that a voltage of a predetermined percent of an expected output voltage is previously added to an APC output voltage of the APC circuit of a laser diode, thereby greatly reducing a stabilizing time necessary for stabilizing an APC output voltage at an initial stage in a write or read mode according to prior art. Therefore, the loss of data in a high speed write or read mode can be reduced. Particularly, the loss of data in a high speed write mode can be greatly reduced.

Description: The present invention relates to a disc drive, and more particularly, to an automatic power control apparatus for reducing time necessary for stabilizing an automatic power control circuit at the initial stage of automatic power control of a disc drive. Disc drives such as CD drives, DVD drives, CD-ROM drives and DVD-ROM drives write a signal to or read a signal from a disc using light. Disc drives write data to a disc by radiating light at the disc from a laser diode and read data from the disc by applying an optical signal to a disc from the laser diode with current lower than writing power, converting light reflected from the disc into an electrical signal using a light receiving diode (i.e., a photodetector), and processing the signal. Such disc drives essentially need a automatic power control (APC) circuit for automatically controlling the driving current of a laser diode to control the power of an optical signal output from the laser diode to be constant in a write or read mode. US 5,309,461 discloses a compensated laser drive circuit incorporating a second source of current for driving a laser during a transient period to eliminate output transience. JP-A-04 345 930 discloses a control system for emitted laser light quantity for an optical disk storage device. A controller sets reference voltages V 1 and V 2 . A light emission quantity control circuit comprises an amplifier and an adder to recieve the reference voltages to set a read output level according to reference voltage V 1 and a write output level according to a summation of V 1 and V 2 . This document forms the precharacterising portion of claim 1 appended hereto. As shown in Figure 1, a conventional APC apparatus includes an operational (OP) amplifier A1, resistors R1 and R2, and a capacitor C1. A reference voltage Ref is applied to the non-inverted input terminal of the OP amplifier A1, and a sampling and holding (S/H) voltage of a signal for monitoring writing power is applied to the inverted input terminal of the OP amplifier A1. Once a command for a write mode is input to a disc drive, an output voltage gradually increases depending on a time constant which is determined by the resistor R1 and the capacitor C1 starting from a point when APC in the write mode begins, as shown in Figure 2(c) An APC stabilizing time (i.e., to in Figure 2(c)) considerably influences the quality of writing. As the APC stabilizing time becomes shorter, an amount of lost data can be reduced. Particularly, as the speed factor of a disc drive gradually increases to 8 and then to 12, the APC stabilizing time at an initial stage of a write mode increasingly influences the writing quality. Accordingly, since a conventional APC apparatus needs some time starting from a point when APC begins until laser power is stabilized, an error occurs before the power of a laser diode reaches a predetermined level due to a deficiency of the output power of the laser diode in a write mode. With a view to solve or reduce the above-described problems, it is an aim of embodiments of the present invention to provide an automatic power control apparatus for reducing a stabilizing time at an initial stage of automatic power control of a laser diode in a disc drive by previously applying an additional predetermined voltage to an automatic power control circuit. According to a first aspect of the present invention, there is provided an automatic power control apparatus of a disc drive, as set forth in claim 1 appended hereto. Preferably, the automatic power control reference voltage signal and the stabilizing compensation voltage signal are analog signals obtained from digital-to-analog converting means included within the controller. The value of the stabilizing compensation voltage signal in a write mode is preferably different from that in a read mode. The stabilizing compensation voltage signal preferably has a voltage no greater than 90% of an automatic power control output voltage in a selected mode. The monitor signal is preferably output from the photo diode of a pickup and then amplified. The monitor signal is preferably inverted and proportional to the output power of the laser diode. The amplifier may be realized as an operational amplifier, and the input and output terminals of the operational amplifier are connected to a resistor and a capacitor in parallel. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 is a diagram of the configuration of an automatic power control apparatus of a disc drive according to prior art; Figure 2 is a waveform diagram of main signals of the apparatus shown in Figure 1; Figure 3 is a diagram of the configuration of an automatic power control apparatus of a disc drive according to an embodiment of the present invention; and Figure 4 is a waveform diagram of main signals of the apparatus shown in Figure 3. As shown in Figure 3, an automatic power control apparatus of a disc drive according to an embodiment of the present invention includes a pickup 301, a driver 302, a controller 303, an adder 304, an amplifier 305 and a sampling and holding (S/H) unit 306. The amplifier 305 may be realized as an operational (OP) amplifier. Although not shown in detail, the pickup 301 includes a laser diode, and a photo diode for optical detection and a variety of optical instruments. The pickup 301 is controlled to move in horizontal and vertical directions by a tracking control signal and a focus control signal. Once a user inputs a command for a write mode into the controller 303, the controller 303 sets automatic power control (APC) reference voltage data which an APC circuit for controlling the power of the laser diode needs and stabilizing compensation voltage data and converts the APC reference voltage data and the stabilizing compensation voltage data into analog signals, thereby generating an APC reference voltage signal Ref shown in Figure 4(b) and a stabilizing compensation voltage signal shown in Figure 4(a). In other words, the controller 303 includes a digital-to-analog converter and converts the APC reference voltage data and the stabilizing compensation voltage data which are digital signals into analog signals, respectively. Here, the APC reference voltage data set in a write mode is different from that set in a read mode. The stabilizing compensation voltage data is set to a voltage value having a predetermined level, which is lower than that of an APC output voltage applied to the laser diode driver 302, in a write mode. The stabilizing compensation voltage data should be set not to go beyond the control range of an APC loop due to external disturbance. For example, it is effective to set the stabilizing compensation voltage data to be no greater than 90% of an expected APC output voltage. In an embodiment of the present invention, the stabilizing compensation voltage data is set to 90% of the APC output voltage. The controller 303 applies the APC reference voltage signal to the amplifier 305 and applies the stabilizing compensation voltage signal to the adder 304. The S/H unit 306 is provided for generating a monitor signal for estimating the power level of an optical signal output from the laser diode of the pickup 301. The S/H unit 306 receives a signal from the photo diode of the pickup 301, amplifies and inverts the input signal, and then samples and holds the signal in a writing section before outputting it to the amplifier 305. Then, the amplifier 305 amplifies the voltage difference between the APC reference voltage signal and the signal sampled and held in the writing section, which are input through its two input terminals, respectively, and outputs the amplified result. The adder 304 adds the output voltage from the amplifier 305 to the stabilizing compensation voltage from the controller 303 and outputs the resultant signal to the driver 302. The APC output voltage, to which the stabilizing compensation voltage reaching 90% of an expected output level is added by the adder 304, is input to the driver 302 so that the APC output voltage has a level corresponding to 90% of the expected output level at the beginning point of APC corresponding to an initial point when writing starts shown in Figure 4(c). Accordingly, only a stabilizing time t s shown in Figure 4(d) necessary for increasing the APC output voltage by the remaining 10% voltage is needed. Consequently, the present invention reduces a stabilizing time to about 1/10 of that necessary according to prior art in which a stabilizing compensation voltage is not previously applied. The driver 302 converts the voltage applied from the adder 304 into laser diode driving current and outputs the current to the laser diode of the pickup 301. Then, the laser diode generates an optical signal having a writing power corresponding to the driving current applied thereto. The optical signal is applied to a disc through an optical system, thereby writing data to the disc. Consequently, the APC control circuit constructs a closed circuit so that a signal, which is obtained by monitoring the power of an optical signal output from the laser diode and then which is sampled and held, is fed back to the amplifier 306 for APC. Therefore, the optical power of the laser diode can be automatically controlled in a write mode. Although only an operation of automatically controlling the power of a laser diode in a write mode is described in this specification, the present invention can automatically control the power of the laser diode in both write and read mode in the same manner. Accordingly, it is apparent that a stabilizing time necessary at an initial stage in a read mode can be reduced by applying a stabilizing compensation voltage to an APC circuit. As described above, according to embodiments of the present invention, an APC circuit is designed such that a voltage equal to a predetermined percentage of an expected output voltage is previously added to an APC output voltage of the APC circuit of a laser diode, thereby greatly reducing a stabilizing time necessary for stabilizing an APC output voltage at an initial stage in a write or read mode according to prior art. Therefore, the present invention can reduce the loss of data in a high speed write or read mode. Particularly, the present invention can greatly reduce the loss of data in a high speed write mode. While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims: An automatic power control apparatus of a disc drive, comprising: a controller (303) for setting an automatic power control reference voltage signal according to a selected mode; an amplifier (305) for receiving the automatic power control reference voltage signal and a signal which is obtained by sampling a writing section of a monitor signal for estimating the level of the output power of a laser diode, through its two input terminals, respectively, and amplifying the voltage difference between the two input terminals with a predetermined gain; and an adder (304) for summing the output of the amplifier (305) and a second voltage signal and outputting the result of the summation to a laser diode driving circuit (302); characterised by : the controller (303) generating a stabilising compensation voltage signal to set a stabilizing compensation voltage as the second voltage signal according to the selected mode; and the adder (304) summing the output of the amplifier (305) and the stabilizing compensation voltage signal and outputting the result of the summation as an output voltage to a laser diode driving circuit (302), thereby reducing a stabilising time to stabilise the output voltage at an initial stage in a selected read or write mode. The automatic power control apparatus of claim 1, wherein the automatic power control reference voltage signal and the stabilizing compensation voltage signal are analog signals obtained from digital-to-analog converting means included within the controller (303). The automatic power control apparatus of any preceding claim, wherein the value of the stabilizing compensation voltage signal in a write mode is different from that in a read mode. The automatic power control apparatus of any preceding claim, wherein the stabilizing compensation voltage signal has a voltage no greater than 90% of an automatic power control output voltage in a selected mode. The automatic power control apparatus of any preceding claim, wherein the monitor signal is output from the photo diode of a pickup and then amplified. The automatic power control apparatus of claim 5, wherein the monitor signal is inverted and proportional to the output power of the laser diode. The automatic power control apparatus of any preceding claim, wherein the amplifier (305) is realized as an operational amplifier, and the input and output terminals of the operational amplifier are connected to a resistor and a capacitor in parallel.

Inventors: GO SUNG-RO, JIN KYOUNG-BOG, LEE JOUNG-HOON, YUN KI-BONG, GO, SUNG-RO, JIN, KYOUNG-BOG, LEE, JOUNG-HOON, YUN, KI-BONG, Yun, Ki-bong, 804-504 Pyuckjeokgol Doosan Apt.
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 2001
Main classification: G11B7
IPC codes: G11B7