1. Technical Field
The present invention relates to an optical disc device for detecting various kinds of signals required for recording and playback of an optical disc, using signals outputted from photodetectors of an optical pickup.
2. Background Art
FIG. 20 is a block diagram illustrating the construction of a conventional optical disc device.
With reference to FIG. 20, the conventional optical disc device comprises a pickup 1000, VGA 1001a˜h, HPF 1002a˜d, comparators 1003a˜d, a phase difference tracking error signal detection circuit 1004, an off track signal generation circuit 1005, a differential RF signal generation circuit 1006, a wobble signal generation circuit 1007, a CAPA detection signal generation circuit 1008, a servo error signal generation circuit 1009, a selector 1010, a selector 1011, an LPF 1012, a comparator 1013, an LPF 1014, an LPF 1015, an LPF 1016, a selector 1017, and an ADC 1018. In order to indicate the specific numbers of the VGA 1001, the HPF 1002, and the comparators 1003, respectively, a pickup having three four-part split photodetectors each comprising four split photodetectors (hereinafter, also referred to as photodetectors) is employed as shown in FIG. 3, and the pickup outputs, as shown in FIG. 3, signals outputted from photodetectors A˜D 32 receiving a main beam (hereinafter referred to as main photodetectors A˜D), and signals outputted from photodetectors E˜H 31 and 33 receiving a sub beam which is applied prior or/and subsequent to the main beam that is applied to the photodetectors A˜D (hereinafter referred to as sub photodetectors E˜H).
The VGA 1001a˜h are gain adjustment amplifiers which receive the signals outputted from the photodetectors A˜H of the pickup 1000, and correct fluctuations in the amplitudes of the photodetector output signals due to reflectivity of playback media, fluctuations in laser power, efficiency of pickup, or the like.
The HPF 1002a˜d remove DC components and level fluctuation components due to flaws on the disc or the like, from the photodetector output signals.
The comparators 1003a˜d binarize RF components of the signals outputted from the HPF 1002a˜d, and output them.
The phase difference tracking error signal detection circuit 1004 is constituted by an analog circuit, and measures phase differences among the four-channels of input signals which are outputted from the comparators 1003a˜d, thereby to generate a phase difference tracking error signal (hereinafter referred to as a DPDTE signal), and outputs the signal.
The off track signal generation circuit 1005 generates an off track signal for detecting off track, from the DPDTE signal outputted from the phase difference tracking error signal detection circuit 1004.
The differential RF signal generation circuit 1006 generates a differential RF signal (hereinafter referred to as a broadband pushpull TE) from the output signal of the four-part split photodetector.
The wobble signal generation circuit 1007 inputs the broadband pushpull TE outputted from the differential RF signal generation circuit 1006 into a BPF constituted by an analog circuit, and extracts a wobble signal that exists when the disc type is DVD-R/RW or DVD-RAM.
The CAPA detection signal generation circuit 1008 detects that the broadband pushpull TE in a CAPA (address mark) portion oscillates up and down during RAM playback, and outputs a CAPA detection signal.
The servo error signal generation circuit 1009 is constituted by an analog circuit, and performs plural patterns of servo matrix operations and balance operations which have been determined in advance according to the construction of the pickup, the recording/playback media, and the recording/playback mode, on the basis of the outputs from the photodetectors of the optical pickup, thereby generating various kinds of servo error signals. The generated servo error signals include a focus error signal (hereinafter referred to as an FE signal), a tracking error signal (hereinafter referred to as a TE signal), and a full addition signal expressing the amount of reflected light (hereinafter referred to as an AS signal).
FIGS. 21, 22, and 23 show examples of matrix operation expressions which are carried out to generate TE signals, FE signals, and AS signals by the servo error signal generation circuit 1009. In these figures, A˜H denote the output signals from the respective photodetectors shown in FIG. 3. Further, a phase difference AB denotes a phase difference between the output signals from the photodetectors A and B, a phase difference CD denotes a phase difference between the output signals from the photodetectors C and D, and k and a denote operation constants, respectively.
In the servo error signal generation circuit 1009, the matrix operations are carried out while switching the operation expressions as shown in FIGS. 21, 22, and 23 according to the pickup structure, the playback media, the playback mode and the like, thereby generating TE signals, FE signals, and AS signals. When performing operations of plural expressions as shown in FIGS. 21, 22, and 23, it is necessary to constitute the servo error signal generation circuit 1009 by an analog circuit which can perform matrix operations according to the respective expressions and an operation of total sum thereof.
Further, the selector 1010 selects a TE signal corresponding to the pickup structure, the playback media, and the playback mode from among the plural TE signals generated by the servo error signal generation circuit 1009 and the TE signal detected by the phase difference tracking error signal detection circuit 1004. The selector 1011 selects an FE signal corresponding to the pickup structure, the playback media, and the playback mode from among the plural FE signals generated by the servo error signal generation circuit 1009.
Thereafter, the LPF 1012 removes noise from the TE signal outputted from the selector 1010, and the comparator 1013 binarizes the TE signal using an average of TE signals outputted from the selector 1010 as a threshold value, thereby to output a track cross signal.
The LPF 1014, LPF 1015, and LPF 1016 are anti-aliasing filters each having a cutoff frequency equal to or lower than ½ of a low-band sampling frequency.
The selector 1017 successively selects the TE signal, the FE signal, and the AS signal, and inputs the signals in the ADC 1018. The selector 1017 and the ADC 1018 for converting the signals outputted from the selector 1017 successively into digital signals are components of a time division AD converter.
The digitized TE signal, FE signal, and AS signal outputted from the ADC 1018 are thereafter input to a servo operation circuit (not shown), wherein digital servo operation is carried out according to these servo error signals, thereby generating a drive signal for a drive system.
Next, the operation of the conventional optical disc device constituted as described above will be described.
The signals outputted from the photodetectors A˜H of the pickup 1000 are input to the VGA 1001a˜h, respectively, wherein gain adjustment is carried out. Then, the outputs from the VGA 1001a˜d corresponding to the output signals from the main photodetectors A˜D are output to the HPF 1002a˜d and to the differential RF signal generation circuit 1006, and the outputs from the VGA 1001a˜h are output to the servo error signal generation circuit 1009.
The outputs from the VGA 1001a˜d corresponding to the output signals from the main photodetectors A˜D are input to the phase difference tracking error signal detection circuit 1004 through the HPF 1002a˜d and the comparators 1003a˜d, whereby a DPDTE signal is generated, and thereafter, an off track signal is generated by the off track signal generation circuit 1005.
Further, the outputs from the VGA 1001a˜d corresponding to the output signals from the main photodetector A˜D are input to the differential RF signal generation circuit 1006, wherein a broadband pushpull TE is generated. Thereafter, during DVD-R/RW or DVD-RAM playback, a wobble signal is generated and outputted by the wobble signal generation circuit 1007. During RAM playback, a CAPA detection signal is generated and outputted by the CAPA detection signal generation circuit 1008.
On the other hand, in the servo error signal generation circuit 1009, the inputted signals from the VGA 1001a˜h are subjected to predetermined matrix operations using plural analog circuits for performing predetermined plural patterns of operations corresponding to the pickup structure, the playback media, and the playback mode, thereby generating TE signals, FE signals, and AS signals.
The plural TE signals and FE signals generated by the servo error signal generation circuit 1009 are input to the selector 1010 and the selector 1011, and a TE signal and an FE signal which correspond to the pickup structure, the playback media, and the playback mode, are selected from among the inputted TE signals and FE signals, respectively. The DPDTE signal generated by the phase difference tracking error signal detection circuit 1004 is also input to the selector 1010.
Then, the TE signal selected by the selector 1010 is output as a track cross signal through the LPF 1012 and the comparator 1013.
Further, the TE signal and the FE signal which are selected by the selector 1010 and the selector 1011, respectively, and the AS signal outputted from the servo error signal generation circuit 1009 are transferred through the LPF 1014, the LPF 1015, the LPF 1016, and the selector 1017, and are successively converted into digital signals by the ADC 1018.
The conventional optical disc device is able to detect signals corresponding to recording and playback of all DVD/CD system optical discs including DVD-RAM/R/RW and CD-R/RW, whereby all the DVD/CD system discs can be played using the single optical disc device.
In the above-mentioned conventional optical disc device, however, the input signal frequency band to the tracking error signal generation circuit 1009 ranges from DC to low frequency (several tens of KHz), while the input signal frequency band to the differential RF signal generation circuit 1006 and the HPF 1002 is a high frequency band ranging from several KHz to several tens of MHz. Therefore, the VGA 1001a˜d should cover both of the frequency bands, and are required of a wide-range gain and offset adjustment function, resulting in an increase in the product costs.
Further, the differential RF signal generation circuit and the wobble signal generation circuit are required to generate a wobble signal and a CAPA detection signal, respectively. In the conventional optical disc device, however, since the differential RF signal generation circuit and the wobble signal generation circuit are constituted by analog circuits, the circuit scale is increased, leading to an obstacle to downsizing of the optical disc device.
Further, since the signal outputted from the analog BPF that is used for generating a wobble signal has significant variations in the band width and the output characteristic of the center frequency, the passband width of the BPF should previously be designed to be wider than the required passband width.
Further, since, in the conventional optical disc device, the servo error signal generation circuit 1009 is constituted by analog circuits as described above, it is necessary to provide plural kinds of analog signals for performing the predetermined plural patterns of operations corresponding to the pickup structure, the playback media, and the playback mode, leading to increases in circuit scale and power consumption.
Since the servo error signal generation circuit 1009 is constituted by analog circuits, when performing the operations shown in FIGS. 21 and 22 using the servo error signal generation circuit 1009, there may occur limitations on adjustment precision of the values k and a which are operation constants, due to limitations on the circuit scale and the like, and further, the adjusted operation constants may be varied, leading to deterioration of S/N.
Furthermore, when performing the operations TE=(TE+)*(1−a)−(T−)*(1+a) and FE=(FE+)*(1−a)−(FE−)*(1+a) shown in FIGS. 21 and 22 using hardware, an analog multiplier is required, and the analog multiplier and other operation circuits cause an offset, which makes it difficult to generate an accurate servo error signal.
Further, when operating the tracking servo using the TE signal, in order to improve S/N, it is desirable that the cutoff frequency of the LPF 1005 is set to a minimum value (usually 50˜80 KHz) within the bounds of not adversely affecting the servo characteristics. During seeking, however, the track cross cycle becomes 100 KHz or more, and therefore, it is necessary to change the cutoff frequency of the LPF 1012 according to the seek velocity, leading to complicated circuit construction and increased circuit scale.
Further, in order to realize digitization of signal processing, AD converters that receive the outputs of the VGA 1001a˜d of the conventional optical disc device may be provided to digitally perform the subsequent signal processing. However, data having a precision of 4 bits or more at a sampling frequency of several tens of MHz is required for each input data as input data to the differential RF signal generation circuit 1006 and to the HPF 1002, while data having a precision of 8 bits or more at a sampling frequency of several hundreds of KHz is required for each input data as input data to the servo error signal generation circuit 1009. Therefore, the AD converters to be connected to the VGA 100a˜d must have a precision of 8 bits or more and a conversion velocity of several tens of MHz, leading to an increase in product costs.
The present invention is made to solve the above-described problems and has for its object to provide an optical disc device for performing recording or playback of plural kinds of optical discs, which can reduce product costs, circuit scale, and power consumption, and detect various kinds of signals of high reliability which are not influenced by variations in temperature characteristics or ICs.