Abstract:
An optical information reproducing apparatus and an optical information reproducing method are capable of restraining the variation of laser power by always detecting a constant amplitude of RF signal, even if there is a irregularity of asymmetry. In the optical information reproducing apparatus for reproducing an information signal recorded on a disk ( 8 ) by irradiating thereon a laser light modulated by an information signal, during reproduction, the control amount (S 4 ) of the power control circuit  11  for controlling the power of the laser light to an optimum value is made the value based on the amplitude level VP−, VP+ of the reproduced information signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical information reproducing apparatus and an optical information reproducing method and is applicable to a reproducing method and a reproducing apparatus of disks such as a magneto-optical disk (MO), a compact disk (CD, CD-ROM) and a digital video disk (DVD). 
     2. Description of the Related Art 
     For example, a conventional recording apparatus for the compact disk being an optical information recording medium of this kind processes data to be recorded and then makes an EFM (Eight-to-Fourteen Modulation) on the data, thereby causing a pit sequence having periods ranging from 3T to 11T with respect to a predetermined basic period T to be formed. Thus, audio data or the like to be recorded. 
     Correspondingly, a compact disk player irradiates the compact disk with a laser beam and receives the returned light, thereby generating a reproduced signal which varies in the signal level dependent on an amount of the returned light and then producing a binary signal from the reproduced signal by a predetermined slice level. 
     Further, this binary signal drives a PLL circuit to produce a reproduced clock, by which the binary signal is sequentially latched. This reproduces data with the periods from 3T to 11T corresponding to the pit sequence framed on the compact disk to be produced. 
     The compact disk player decodes the thus reproduced data by the data processing corresponding to the data processing during recording and reproduces audio data or the like recorded on the compact disk. 
     In this context, every optical disk has different characteristics of the degree of modulation, the reflective factor and the like. For this reason, in the optical disk reproducing apparatus, there is provided a laser power control circuit having a function which prevents the deterioration of reproduced signal level by controlling the level of reproduced RF signal to be kept constant. 
     FIG. 5 shows a block diagram of the laser power control circuit of a conventional optical disk device. The optical disk device to which the laser power control circuit is applied comprises an auto power control (APC) circuit  1 , an invertor  6 , a laser  7  emitting a laser light, a disk  8  irradiated with the laser light, a detector  9  detecting the reflected light of the laser light irradiating the disk  8 , a RF amplifier  10  amplifying the reproduced signal detected by the detector  9 , and a laser power control (LPC) circuit  11  detecting an amount of control for controlling the laser power. 
     The APC circuit  1  includes a detector  2  monitoring the irradiating light of laser  7 , an amplifier  3  amplifying the monitored level by the detector  2 , an adder  4  adding the monitored level amplified by the amplifier  3  and input to its adding input terminal (+) and an operating signal detected by the LPC circuit  11  and input to its subtracting input terminal (−). 
     The LPC circuit  11  includes an attenuator (ATT)  12  attenuating a reproduced RF signal SI amplified by the RF amplifier  10  by a predetermined level, a high pass filter (HPF)  13  passing a high frequency component of the reproduced RF signal SI, a peak hold circuit  15  detecting and holding a peak value in outputs of the ATT  12  and HPF  13 , an adder  20  adding an output of the peak hold circuit  15  input to its subtracting input terminal (−) and a target level A input to its adding input terminal (+) for outputting an operating signal, and an amplifier  5  amplifying an output of the adder  2 . 
     The thus configured laser power control circuit of the conventional optical device operates as follows. The reproduced RF signal SI detected by the detector  9  is supplied to the RF amplifier  10 . The reproduced RF signal SI is amplified by the RF amplifier  10 . The amplified RF signal SI is supplied to the ATT  12  and the HPF  13  of LPC circuit  11 . 
     The RF signal S 1  is attenuated by the predetermined level in the ATT  12  of LPC circuit  11 . A DC (direct current component) of the RF signal is cut off to pass its high frequency component by the HPF  13 . The attenuated output of ATT  12  and a high frequency output RFAC (S 2 ) of HPF  13  are supplied to the peak hold circuit  15 . The peak hold circuit  15  holds a peak value of an added version of the attenuated output ATT  12  and the high frequency output of HPF  13  for outputting. The peak output of peak hold circuit  15  is supplied to the subtracting input terminal (−) of the adder  20 . The target level value A is supplied to the adding input terminal (+) of the adder  20 . The adder  20  compares the peak output with the target level value A to output a difference between them as the operating signal which is amplified by the amplifier  5 . 
     The operating signal is supplied to the subtracting input terminal (−) of the adder  4  of APC circuit  1 . The irradiating light of laser is incident on the detector  2  of APC circuit  1  and the detector  2  monitors the irradiating light of laser  7 . A voltage which is monitored by the detector  2  is supplied to the amplifier  3  to be amplified. The monitored voltage amplified by the amplifier  3  is supplied to the adding input terminal (+) of the adder  4 . The adder  4  compares the operating signal detected by the LPC circuit  11  with the monitored voltage to output its difference (an amount of operation). A controlling output of the APC circuit  1  is supplied to the invertor  6  where it is inverted and supplied to the laser  7 . The laser  7  emits the laser light based on the inverted controlling output. The laser light irradiates the surface of disk  8  and the detector  9  detects the reflected light, thereby allowing an information signal to be reproduced. 
     In this case, the peak value of the high frequency output RFAC (S 2 ) of HPF  13  which passes the RF signal S 1  from the RF amplifier  10  and cuts off the DC (direct current component) of RF signal S 1  is the controlling signal, which is peak-held. This peak value of RFAC (S 2 ) is compared with the level A (½× (the target value of amplitude value of the RF signal)) and its difference is impressed on the APC circuit  1  to control the laser power. 
     This makes the level of laser power to be restricted to an RF signal level established by the target level A. Here, the peak-held attenuated output of ATT  12  is used for detecting the amount of control. This is on purpose that even if the information signal is reproduced from the disk  8 , e.g., with very low degree of modulation, the level of RF signal S 1  can be ensured by detecting the operating signal from the LPC circuit  11 . In other words, in case of the disk with very low degree of modulation, the amplitude of RF signal is small so that LPC circuit  11  operates to raise the laser power. Thus, a chain of ATT  12  is inserted in order that the RF signal is destroyed due to that operation. 
     In the above described laser power control circuit of the conventional optical disk device, in order to detect the amplitude of RF signal S 1 , only the peak value (VP+) of the high frequency output RFAC (S 2 ) of HPF  13  is peak held as the amount of control by the peak hold circuit  15 . However, because the characteristics of degree of modulation, reflective factor, etc. are different in every disk  8 , the pits on the disk  8  become slightly longer or shorter by the same amount in the longitudinal forward and backward direction and so there is an irregularity of asymmetry at every disk  8 . As shown in FIG. 6, the RF signal includes signals ranging from I 3  to I 11  between zero level and I top, but only signals within ±20% from the center of amplitude can satisfy the asymmetry standard. Because there is the irregularity of asymmetry in this manner, even the high frequency output RFAC (S 2 ) of HPF  13  which cuts off the DC (direct current component) of the RF signal S 1  includes signals corresponding to signals having a DC offset as shown in FIG.  7 . 
     Therefore, if only the peak value (VP+) of the high frequency output RFAC(S 2 ) of HPF  13  is used as the amount of control, because the peak value is controlled to be the target value, the maximum amplitude VP−P of the constant RF signal S 1  which is an original object of the laser power control circuit will not be available. For example, in case of FIG. 7, because there is a positive offset, the peak value VP+ will be greater than VP+&gt;½· (VP−P). Thus, the amplitude VP−P of RF signal will be controlled to be smaller than the target level. 
     Further, in the optical disk device, when an optical pickup is moved from the inner circumference to the outer circumference (or from the outer circumference to the inner circumference) of the disk  8 , for example, during the track jump TJ or sled kick, the RF signal (S 1 ) as shown in FIG.  8 A and the high frequency output RFAC (S 2 ) of HPF  13  as shown in FIG. 8B will occur. As described above, because the peak value of the RFAC (S 2 ) is used as the amount of control in the laser power control, the amplitude of RF signal is controlled to be greater than the target level during the movement of pickup, so that the laser power and the RF signal level will be raised in vain. This will cause an inconvenience that a life of the laser is shortened and also another inconvenience that a deviation of the gain adjustment occurs when the automatic adjustment of the servo system such as the tracking servo or the like is performed. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the foregoing points, and intends to propose an optical information reproducing apparatus and an optical information reproducing method which is capable of restraining a variation of the laser power by detecting the constant RF signal amplitude at all times even if there is the unevenness of asymmetry. 
     In order to solve such problem, the present invention provides an optical information reproducing apparatus for reproducing an information signal, which is recorded on an optical recording medium by irradiating a laser light modulated by an information signal on the optical information recording medium, wherein during reproduction the control amount of the laser power control circuit for controlling the power of laser light to be an optimum value is made a value based on an amplitude level of the information signal upon reproduction. 
     Also, the present invention provides an optical information reproducing method for reproducing an information signal, which is recorded on an optical recording medium by irradiating a laser light modulated by an information signal on the optical information recording medium, wherein during reproduction the control amount in the laser power control for controlling power of the laser light to be an optimum value is made a value based on an amplitude level of the information signal upon reproduction. 
     An operation according to the optical information reproducing apparatus and the optical information reproducing method of the present invention is as follows. 
     During reproduction, the laser power control circuit produces the control amount for controlling the power of the laser light to be an optimum value in reproduction. The laser power control circuit outputs as an operating signal a difference from the target level value so as to make this control amount to be a value based on an amplitude level of the information signal upon reproduction. 
     The laser power control circuit makes the value based on the amplitude level of information signal to be a value of the amplitude level of the reproduced high frequency signal or a DC signal proportional to the amplitude level of the reproduced high frequency signal, for outputting as the operating signal the difference from the target level value. 
     The laser power control circuit detects the peak value at a bottom level of the reproduced high frequency signal by peak hold, adds the bottom peak value detected by the peak hold and the reproduced high frequency signal, peak-holds the added output signal, and outputs as the operating signal the difference from the target level value so as to detect the reproduced high frequency signal or the DC signal proportional to the amplitude level of the reproduced high frequency signal. 
     The laser power control circuit shifts the information signal in reproduction by its bottom peak value and produces a waveform having the maximum amplitude from zero level. The laser power control circuit compares this peak value of the maximum amplitude with a target amplitude value of the information signal upon reproduction, makes its difference or the signal proportional thereto to be the amount of operation, and applies this to the laser for controlling the laser power. 
     The amount of operation is supplied to the laser. The laser emits the laser light according to the amount of operation. The laser light is made to irradiate the disk surface and the reflected light is detected to reproduce the information signal. This restricts the level of laser power to the level of reproduced information signal established by the target level. 
     In this way, by making the amplitude of information signal upon reproduction to be the amount of control in the laser power control, even if there is the irregularity in the reproduced information signal, it will be possible to always obtain a constant amplitude of the information signal upon reproduction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the laser power control circuit of the optical disk device according to an embodiment of the present invention; 
     FIG. 2 is a diagram showing a signal waveform of the laser power control circuit according to the embodiment of the present invention; 
     FIG. 3 is a block diagram showing another laser power control circuit of the optical disk device according to the embodiment of the present invention; 
     FIG. 4 is a block diagram showing a still another laser power control circuit of the optical disk device according to the embodiment of the present invention; 
     FIG. 5 is a block diagram showing the laser power control circuit of the conventional optical disk device; 
     FIG. 6 is a waveform diagram used to explain the conventional asymmetry standard; 
     FIG. 7 is a waveform diagram showing an example of the conventional RFAC signal; and 
     FIG. 8, having FIGS. 8A and 8B, are waveform diagrams showing examples of the conventional signals during a track jump, in which FIG. 8A shows an RF signal (S 1 ) and FIG. 8B shows an RFAC signal (S 2 ). 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments according to the present invention will now be described below in detail with reference to the accompanying drawings. 
     FIG. 1 is a block diagram showing a configuration of the laser power control circuit of the optical disk device according to an embodiment of the present invention, which will be described below in detail. Further, in the configuration of the laser power control circuit of the optical disk device shown in FIG. 1, parts corresponding to those of the laser power control circuit of the conventional optical disk device shown in FIG. 5 are denoted by the same reference numerals to omit its description. 
     FIG. 1 is a block diagram showing a laser power control circuit for an optical disk device according to an embodiment of the present invention. An optical disk device to which the laser power control circuit is applied comprises an automatic power control (APC) circuit  1 , an invertor  6 , a laser  7  for emitting a laser light, a disk  8  which is irradiated with the laser light, a detector  9  for detecting the reflected light of the laser light irradiated on the disk  8 , an RF amplifier  10  for amplifying a reproduced signal detected by the detector  9  and a laser power control (LPC) circuit  11  for detecting an operation signal of the laser power. 
     The APC circuit  1  includes a detector  2  for monitoring the irradiating light of laser  7 , an amplifier  3  for amplifying the monitored level by the detector  2  and an adder  4  for adding the monitored level amplified by the amplifier  3  input to the adding input terminal (+) and the operating signal detected by the LPC circuit  11  input to the subtracting input terminal (−). 
     The LPC circuit  11  includes an attenuator (ATT)  12  for attenuating a reproduced RF signal S 1  amplified by the RF amplifier  10  by a predetermined level, a high pass filter (HPF)  13  for cutting off a DC (direct current component) of the reproduced RF signal S 1  to pass the high frequency component, an invertor  14  for inverting an output RFAC (S 2 ) of HPF  13 , an peak hold circuit  15  for detecting a peak value S 3  of the inverted output of HPF  13  to hold it, an adder  16  for adding the output S 2  of HPF  13  and a peak value S 3  of the inverted output of HPF  13 , a peak hold circuit  17  for detecting and holding a peak value S 5  of the ATT  12  and an added output S 4 , an adder  18  for adding the output of peak hold circuit  17  input to a subtracting input terminal (−) and a target level A input to an adding input terminal (+) to output an operating signal S 6 , and an amplifier  5  for amplifying an output of the adder  18 . 
     The laser power control circuit  11  has a function to produce a control amount S 4  for controlling power of the laser light to be an optimum value in reproduction, that is, a function to make the control amount S 4  to be a value based on the amplitude level of information signal upon reproduction and to output the difference from the target level value as the operating signal S 6 . 
     The laser power control circuit  11  has also a function to output the difference from the target level value as the operating signal S 6  so that the value based on the amplitude level of information signal may become a value of the amplitude level of reproduced high frequency signal or the DC signal proportional to the amplitude level of reproduced high frequency signal. 
     The laser power control circuit  11  has a function to detect the peak value S 3  of bottom level VP− of the reproduced high frequency signal by peak hold, add the bottom peak value S 3  detected by the peak hold and the reproduced high frequency signal S 1 , peak-hold the added output signal S 4 , and output the difference from the target level value A as the operating signal S 6  so as to detect the reproduced high frequency signal or the DC signal proportional to the reproduced high frequency signal. 
     The laser power control circuit  11  has also a function to shift the information signal upon reproduction by the amplitude VP−and produce a waveform having the maximum amplitude VP−P from zero level. The laser power control circuit  11  compares the peak value of the maximum amplitude VP−P with the amplitude target level A of the information signal upon reproduction and outputs its difference as the operating signal S 6  which is supplied to the amplifier  5  to be amplified. This is applied to the laser  7  as the amount of operation for controlling the laser power. 
     The adder  16  in the laser power control circuit  11  forms an peak-hold means for peak-holding the peak value S 3  of the bottom level VP− of reproduced high frequency signal S 1  and an adding means for adding the bottom peak value S 3  derived by the peak-hold and the reproduced high frequency signal S 1 . The peak-hold circuit  17  forms an peak-hold means for peak-holding the added output signal S 4 . 
     The thus configured laser power control circuit of the optical disk device according to the present embodiment operates as follows. 
     The reproduced RF signal detected by the detector  9  is supplied to the RF amplifier  10  which amplifies the reproduced RF signal. The RF signal S 1  is supplied to the ATT  12  and the HPF  13  of the LPC circuit  11 . 
     The RF signal S 1  is attenuated by a predetermined level in the ATT  12  of the LPC circuit  11 . The DC (direct current component) of RF signal S 1  is cut off in the HPF  13  to pass its high frequency component. 
     The high frequency output RFAC (S 2 ) of HPF  13  is inverted by the invertor  14  and then supplied to the peak hold circuit  15 . The peak hold circuit  15  holds and outputs the peak value S 3  of the inverted output of high frequency output RFAC (S 2 ) of HPF  13 . The high frequency output S 2  of HPF  13  and the peak value S 3  of the inverted output of S 2  from the peak hold circuit  15  are supplied to the adding input terminals (+) of the adder  16 . The adder  16  adds the high frequency output S 2  of HPF  13  and the peak value S 3  from peak circuit  15  of the inverted output of S 2  to output the added output S 4  (the control amount). The attenuated output of ATT  12  and the added output S 4  are supplied to the peak hold circuit  17 . 
     The peak hold circuit  17  holds and outputs the peak value of an added version of the attenuated output of ATT  12  and the high frequency output of HPF  13 . The peak output S 5  of peak hold circuit  17  is supplied to the subtracting input terminal (−) of the adder  18 . The target level value A is supplied to the adding input terminal (+) of adder  18 . The adder  18  adds the peak output S 5  and the target level value A to output its difference as the operating signal S 6 . 
     The operating signal S 6  is supplied to the amplifier  5  to be amplified and then supplied to the subtracting input terminal (−) of the adder  4  in the APC circuit  1 . The irradiating light of laser  7  is incident on the detector  2  in the APC circuit  1  and the detector  2  monitors the irradiating light of laser  7 . The monitored voltage by the detector  2  is supplied to the amplifier  3  to be amplified. The monitored voltage amplified by amplifier  3  is supplied to the adding input terminal (+) of adder  4 . The adder  4  adds the operating signal S 6  detected by LPC circuit  11  and the monitored voltage to output its added result. The controlling output (the operation amount) of APC circuit  1  is supplied to the invertor  6  and then to the laser  7  after being inverted. The laser  7  emits the laser light based on the inverted controlling output. The laser light is irradiated on the surface of disk  8  and the reflected light is detected by the detector  9 , thereby enabling the information signal to be reproduced. 
     In this case, the RF signal S 1  from RF amplifier  10  is caused to pass the HPF  13  which cuts off the DC (direct current component) of RF signal S 1  and the high frequency output RFAC (S 2 ) of HPF  13  is inverted. The peak value S 3  of the inverted output of high frequency output RFAC (S 2 ) from HPF  13  is peak-held and this peak value S 3  of RFAC (S 2 ) is added to the high frequency output RFAC (S 2 ) of HPF  13 . The added output S 4  forms the waveform having the maximum amplitude VP−P from zero level as shown in FIG. 2 because the RFAC shown in FIG. 7 is DC-shifted by an amount for the amplitude VP−in the positive direction. The peak value S 5  resulting from peak-holding the added output S 4  forms the value of VP−P. The peak value S 5  is used as a main feedback value and compared with the amplitude target value A of RF signal. The difference between them is impressed on the APC circuit  1  to control the laser power. 
     In this way, the level of laser power is restricted to the RF signal level established by the target level A. Besides, the attenuated output of ATT  12  is peak-held to be used for detecting the amount of control S 4 . This is on purpose to ensure the level of RF signal S 1  by detecting the operating signal S 6  from the LPC circuit  11 , even if the recording or reproduction of the information signal is performed on the disk  8  e.g. having very low degree of modulation. 
     Thus, by making the amplitude VP−P of RF signal to be the control amount S 4  for laser power control, it will be possible to always obtain the constant amplitude of RF signal, even if there is the unevenness of asymmetry. In addition, because the amplitude of RF signal can always be detected, it will be possible to restrain the variation of laser power during the movement of optical pickup such as the track jump and so on. 
     FIG. 3 is a block diagram showing a configuration of another laser power control circuit of an optical disk device according to the embodiment of the present invention. Further, in the configuration of the laser power control circuit of an optical disk device shown in FIG. 3, corresponding parts to those of the laser power control circuit shown in FIG. 1 are denoted by the same reference numerals to omit its description. The other laser power control circuit of the optical disk device shown in FIG. 3 is an improved version of the laser power circuit. The only different points from the configuration shown in FIG. 1 are described below. 
     The LPC circuit  11  comprises the attenuator (ATT)  12  for attenuating by the predetermined level the reproduced RF signal S 1  amplified by RF amplifier  10 , the high pass filter (HPF)  13  for cutting off the DC (direct current component) of reproduced RF signal S 1  to pass its high frequency component, the peak hold circuit  15  for detecting and holding the peak value of output RFAC S 2  of HPF  13 , the invertor  14  for inverting the peak value to output an inverted output S 3 ′, the adder  16  for adding the output S 2  of HPF  13  and the inverted output S 3 ′ of peak value of the output from HPF  13 , the peak hold circuit  17  for detecting and holding a peak value S 5 ′ of the output of ATT  12  plus the added output S 4 ′, the adder  18  for adding the output S 5 ′ of peak hold circuit  17  input to the subtracting input terminal (−) and the target level A input to the adding input terminal (+) to output an operating signal S 6 ′, and the amplifier  5  for amplifying the output of adder  18 . 
     The thus configured laser power control circuit of optical disk device according to the present embodiment operates as follows. 
     The RF signal S 1  is attenuated by the predetermined level in the ATT  12  of LPC circuit  11 . The DC (direct current component) of RF signal S 1  is cut off in the HPF  13  to pass its high frequency component. 
     The high frequency output RFAC S 2  of HPF  13  is supplied to the peak hold circuit  15 , which holds the peak value of high frequency output RFAC S 2  of HPF  13 . The invertor  14  inverts that peak value to output the inverted output S 3 ′. The high frequency output S 2  from HPF  13  and the inverted output S 3 ′ of the peak value of S 2  from peak hold circuit  15  are supplied to the respective adding input terminals (+) of adder  16 . The adder  16  adds the high frequency output S 2  of HPF  13  and the inverted output S 3 ′ of the peak value of S 2  from peak hold circuit  15  to output the added output S 4 ′ (the control amount). The attenuated output of ATT  12  and the added output S 4 ′ are both supplied to the peak hold circuit  17 . 
     The peak hold circuit  17  holds the peak value S 5 ′ of an added version of the attenuated output of ATT  12  and the high frequency output of HPF  13  for outputting. The peak output S 5 ′ of peak hold circuit  17  is supplied to the subtracting input terminal (−) of adder  18 . The target level value A is supplied to the adding input terminal (+) of adder  18 . The adder  18  compares the peak output S 5 ′ with the target level value A to output its difference as the operating signal S 6 ′. 
     In this case, the RF signal S 1  from RF amplifier  10  is made to pass the HPF  13  and the peak value of the high frequency output RFAC (S 2 ) of HPF  13  which cuts off the DC (direct current component) of RF signal S 1  is peak-held to add the inverted output S 3 ′ obtained by inverting the peak value of RFAC (S 2 ) and the high frequency output RFAC (S 2 ) of HPF  13 . The added output S 4 ′ forms the waveform having the maximum amplitude VP−P from zero level as shown in FIG. 2, because the RFAC shown in FIG. 7 is DC-shifted by an amount for the amplitude VP− in the positive direction in the same manner as S 4 . The peak value S 5 ′ obtained by peak-holding the added output S 4 ′ becomes the value of VP−P. The peak value S 5 ′ is used as the main feedback value and compared with the amplitude target value A of RF signal. The difference between them is impressed on the APC circuit  1  as the operating signal S 6 ′ to control the laser power. 
     This causes the level of laser power to be restricted to the RF signal level established by the target level A. 
     Thus, by making the amplitude VP−P of RF signal to be the control amount S 4 ′ for laser power control, it will be possible to always obtain the constant amplitude of RF signal, even if there is the irregularity of asymmetry. In addition,because the amplitude of RF signal can always be detected, it will be possible to restrain the variation of laser power during the movement of optical pickup such as the track jump or the like. 
     FIG. 4 is a block diagram showing a configuration of still another laser power control circuit of optical disk device according to the embodiment of the present invention. Further, in the configuration of still another laser power control circuit of optical disk device shown in FIG. 4, corresponding parts to those of the laser power control circuit shown in FIG. 1 are denoted by the same reference numerals to omit its description. The still another laser power control circuit of optical disk device shown in FIG. 4 is an improved version of the laser power control circuit. The only different points from the configuration shown in FIG. 1 are described below. 
     The LPC circuit  11  comprises the attenuator (ATT)  12  for attenuating the reproduced RF signal S 1  amplified by RF amplifier  10  by the predetermined level, an invertor  14  for inverting the RF signal S 1 , a peak hold circuit  15  for detecting and holding a peak value S 3 ″ of the inverted output, an adder  16  for adding the RF signal S 1  and the peak value S 3 ″ of the inverted output, the peak hold circuit  17  for detecting and holding a peak value S 5 ″ of the ATT  12  plus the added output S 4 ″, the adder  18  for adding the output of peak hold circuit  17  input to the subtracting input terminal (−) and the target level A input to the adding input terminal (+) to output the operating signal S 6 ″, and the amplifier  5  for amplifying the output of adder  18 . 
     The thus configured laser power control circuit of optical disk device according to the present embodiment operates as follows. 
     The RF signal S 1  is inverted by the invertor  14  and then supplied to the peak hold circuit  15  which holds the peak value S 3 ″ of the inverted output of RF signal S 1  for outputting. The RF signal S 1  and the peak value S 3 ″ from peak hold circuit  15  are supplied to the respective adding input terminals (+) of adder  16 . The adder  16  adds the RF signal S 1  and the peak value S 3 ″ from peak hold circuit  15  to output the added output S 4 ″ (the control amount). The attenuated output of ATT  12  and the added output S 4 ″ are both supplied to the peak hold circuit  17 . 
     The peak hold circuit  17  holds the peak value S 5 ″ of an added version of the attenuated output of ATT  12  and the added output S 4 ″ for outputting. The peak output S 5 ″ of peak hold circuit  17  is supplied to the subtracting input terminal (−) of adder  18 . The target level value A is supplied to the adding input terminal (+) of adder  18 . The adder  18  adds the peak output S 5 ″ and the target level value A to output its difference as the operating signal S 6 ″. 
     In this case, the RF signal SI from RF amplifier is inverted and the peak value S 3 ″ of the inverted output of RF signal S 1  is peak-held to add the peak value S 3 ″ of the inverted output of RF signal S 1  and the RF signal S 1 . The added output S 4 ″ becomes a waveform in which the DC component to be cut off by HPF  13  is added to S 4  and the RFAC shown in FIG. 7 is DC-shifted by an amount for the amplitude VP− in the positive direction. Thus, the waveform has the maximum amplitude VP−P from zero level as shown in FIG.  2 . The peak value S 5 ″ obtained by peak-holding the added output S 4 ″ becomes the value VP−P. The peak value S 5 ″ is made the main feedback value and compared with the amplitude target value A of RF signal. The difference between them is applied to the APC circuit  1  as the operating signal S 6 ″ to control the laser power. 
     This causes the level of laser power to be restricted to the RF signal level established by the target level A. 
     In this way, by using the amplitude VP−P of RF signal as the control amount S 4 ″ for the laser power control, it will be possible to always obtain the constant amplitude of RF signal, even if there is the unevenness of asymmetry. In addition, because the amplitude of RF signal can always be detected, it will be possible to restrain the variation of laser power during the movement of optical pickup such as the track jump and so on. 
     Having described preferred embodiments of the present invention with reference to the accompanying drawings, it is to be understood that the present invention is not limited to the above-mentioned embodiments and that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit or scope of the present invention as defined in the appended claims.