JPH0522973B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a disc playback device such as an optical compact disc player, and particularly relates to an improvement of a servo circuit thereof. [Technical Background of the Invention] As is well known, in the fields of audio equipment, image equipment, etc., analog information signals are converted into digitized data in order to record and reproduce data with as high density and high fidelity as possible. Optical disc playback devices have become popular, which record digital data on a disc and optically read digitized data from the disc to obtain the original analog information signal. In the optical disc playback device as described above, the objective lens provided in the optical pickup is normally biased to the initial position by a spring or the like, and when the disc playback starts, the focus actuator coil A focus search is performed by supplying a focus search signal to and moving the objective lens to the vicinity of the in-focus position. Then, when the objective lens reaches near the in-focus position,
Thereafter, a focus servo is applied to keep the objective lens at the in-focus position, and a tracking servo is applied so that the objective lens can accurately follow the pit row recorded on the disk. It is something that is regenerated. In this case, switching from focus search to focus servo is performed by determining whether the objective lens has reached the vicinity of the in-focus position in the focus search state based on the output signal level from the pick-up.
This is done by outputting a focus OK signal. In addition, in the focus servo and tracking servo states, for example, if a scratched part on the disk is played or vibration is applied from the outside, the type of failure is determined and the gain up signal is changed to the gain down signal. It is also possible to generate a signal to change the focus servo gain or tracking servo gain so that a good reproduced signal can always be obtained. On the other hand, this type of disc reproducing apparatus is also capable of performing an address search for quickly selecting a desired data portion from among the digitized data recorded on the disc. This address search is performed by moving the pick-up or the objective lens itself in the radial direction of the disk at high speed, and at this time, the ripple components of the RF signal generated when the objective lens crosses the pit row are counted. By doing so, the movement is performed while detecting the amount of movement. In this case, control is performed to stop the focus servo and tracking servo by generating a gain-off signal in response to the address search request. The main operations of the disc playback device are the focus search, focus servo, tracking servo, and address search mentioned above, and the focus OK control controls each of these operations.
The signals, gain-up signal, gain-down signal, gain-off signal, etc., are all generated and output by a signal processing circuit composed of a microcomputer or the like. Here, FIG. 3 shows the configuration of a conventional optical compact disc player using a three-beam pickup. That is, numeral 11 in the figure is a main light receiving section that receives a main light beam that is irradiated onto a disk (not shown) and reflected. This main light receiving section 11 has four light receiving regions, and among the output signals A to D from these light receiving regions, A and C and B and D are respectively added as currents, and the current is added to the current-voltage conversion circuit 12. , 13. Each output signal from these current-voltage conversion circuits 12 and 13 is subtracted by a subtraction circuit 14 to generate a focus error signal FEO, and an addition circuit 15
are added to generate the RF signal RFO. Among these, the focus error signal FEO is
Each first fixed terminal 16 of the changeover switch 16, 17
a, 17a, respectively. Further, the RF signal RFO has its DC component removed via the coupling capacitor C ₁ , and is then supplied to a demodulation/reproduction system (not shown) and also to the RF ripple signal generation circuit 18 . This RF ripple signal generation circuit 18 detects the envelope component of the RF signal RFO and generates an RF ripple signal RFRP corresponding to the ripple component. 19a. On the other hand, in the vicinity of the main light receiving section 11, sub light receiving sections 20 and 21 are installed to receive a pair of sub light beams that are irradiated onto the disk and reflected. Each output signal E, F from these sub-light receiving sections 20, 21 is transmitted to a current-voltage conversion circuit 22, 23, respectively.
is supplied to Each output signal from these current-voltage conversion circuits 22 and 23 is subtracted by a subtraction circuit 24 to generate a tracking error signal TEO, and added by an addition circuit 25 to include scratch information on the disk. Sub beam addition signal
SBAD is generated. Of these, the above tracking error signal TEO
is the second fixed terminal 16 of the changeover switch 16
b, and is also supplied to the tracking actuator coil via an output circuit (not shown), and is provided to the tracking servo. Further, the sub-beam addition signal SBAD is supplied to the second fixed terminal 19b of the changeover switch 19. Here, the reference voltage VREF is applied to the second fixed terminal 17b of the changeover switch 17. The common terminal 1 of this changeover switch 17
7c is connected to a focus actuator coil (not shown) via an output circuit 27 consisting of an operational amplifier 26 and resistors _R1 to _R3 . Also,
A switch 28 is connected to the input terminal of the output circuit 27.
A focus search signal generation circuit 29 is connected through the link. The changeover switch 17 and switch 28 are controlled by being supplied via a buffer circuit 31 with a focus OK signal FOK output from a signal processing circuit 30 which will be described later. In other words, the changeover switch 17 is in focus mode.
When the signal FOK is at H level, which corresponds to the fact that the objective lens is located near the in-focus position, the common terminal 17c is switched and connected to the first fixed terminal 17a, and the objective lens is located near the in-focus position. When the common terminal 17c is at L level, which corresponds to the fact that the common terminal 17c is not connected, the common terminal 17c is switched and connected to the second fixed terminal 17b. Further, the switch 28 is turned off when the focus OK signal FOK is at the H level, and turned on when the focus OK signal FOK is at the L level. Therefore, at the start of disc playback, the objective lens is not located near the in-focus point, so the focus OK signal FOK is at the L level, and the focus search signal output from the focus search signal generation circuit 29 is output from the switch 28. The signal is supplied to the focus actuator coil via the output circuit 27, where a focus search is performed. Then, when the objective lens reaches near the in-focus position, a focus OK signal is sent.
Since FOK becomes H level, the focus error signal FEO is supplied to the focus actuator coil via the changeover switch 17 and the output circuit 27, and focus servo is performed here. . Next, common terminals 16c and 19c of the changeover switches 16 and 19 are connected to amplifier circuits 32 and 3, respectively.
3 to the signal processing circuit 30. This signal processing circuit 30 processes various signals based on the RF ripple signal RFRP, sub-beam addition signal SBAD, focus error signal FEO, tracking error signal TEO, etc. that are selectively inputted via the changeover switches 16 and 19. A select signal for generating servo control signals, that is, the gain up signal, gain down signal, gain off signal, up/front focus OK signal, etc., and for switching the changeover switches 16 and 19.
It performs the action of generating SEL ₁ and SEL ₂ . The select signals SEL ₁ and SEL ₂ are used to control the switching of the changeover switches 16 and 19 via buffer circuits 34 and 35, respectively. [Problems in the Background Art] However, when the conventional servo means as described above is integrated into an integrated circuit, it is necessary to input the focus OK signal FOK and the select signals SEL ₁ and SEL ₂ output from the signal processing circuit 30. Three input terminals are required, which increases the number of pins and increases the size. In addition, the signal processing circuit 30
Since the focus OK signal FOK and select signals SEL ₁ and SEL ₂ outputted from the switch are normally at C-MOS level, they are sent to each changeover switch 16, 17,
19 and the switch 28, the buffer circuits 31, 34,
35 is required, which increases the number of elements and also causes the problem of increasing the size. [Object of the Invention] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an extremely good servo circuit for a disc playback device that can reduce the number of pins when integrated into an integrated circuit. [Summary of the Invention] That is, the servo circuit of a disc reproducing device according to the present invention is a disc reproducing device that optically reads an information signal from a disc on which the information signal is recorded. a first switching means for selectively guiding a first signal having information corresponding to a scratch on the disk and a second signal having information corresponding to a scratch on the disk; and a first switching means for selectively guiding a focus error signal and a tracking error signal. a second switching means, a third switching means for selectively switching between a focus search state and a focus servo state, and a servo control signal based on each signal derived by the first and second switching means. signal processing means for generating a selection signal that takes a first to third electrical state in order to control switching of the first to third switching means;
The selection signal output from this signal processing means is the first
and selecting a second signal in a second electrical state;
a first switching signal for controlling switching of the first switching means so as to select the first signal in a third electrical state; A second control unit that controls the switching of both the second and third switching means so that the focus search state is selected respectively, and the tracking error signal and the focus servo state are respectively selected in the second and third electrical states. By providing a switching signal generating means for generating the switching signal No. 2, the number of pins can be reduced when integrated circuits are integrated. [Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 3 are designated by the same symbols, and only the different parts will be described here. That is, the signal processing circuit 30 outputs one select signal SEL.
is output to the 3-state detection circuit 36. This select signal SEL can take three values: an H level state, a high impedance state, and an L level state. The three-state detection circuit 36 selectively outputs H-level and L-level signals from its two output terminals a and b, depending on the state of the select signal SEL, and outputs signals at the H level and L level from the two output terminals a and b, respectively, to the respective changeover switches 16 and 17. , 19 and switch 28. Here, FIG. 2 shows the above three-state detection circuit 3.
This figure shows the details of 6. This 3-state detection circuit 36 includes resistors R ₄ to R ₈ and a level comparator 37,
It is composed of 38 pieces. And the above resistance R ₄ ,
_R5 functions to halve the power supply voltage _Vcc and supply it to the non-inverting input terminals (+) and inverting input terminals (-) of the level comparators 37 and 38. Also,
The resistors R ₆ to _{R 8} have the function of determining the threshold voltages V ₁ and V ₂ to be applied to the inverting input terminals (-) and non-inverting input terminals (+) of the level comparators 37 and 38. be. The relationship is V ₁ > 1/2V _cc > V ₂ . Here, set the level of the select signal SEL to H.
When the select signal SEL is at the H level, SEL= _{V cc > V 1 >} V _2. As a result, output terminal a becomes H level and output terminal b becomes L level. Further, when the select signal SEL is high impedance HiZ, V ₁ >SEL=1/2·V _cc >V ₂ and both output terminals a and b become L level.
Further, when the select signal SEL is at the L level, V ₁ >V ₂ >SEL=0 [V], so the output terminal a becomes the L level and the output terminal b becomes the H level. The above input/output relationships are summarized in the following table.

[Table] In other words, the outputs of the output terminals a and b are determined depending on the state of the select signal SEL. Here, the output from the output terminal a of the three-state detection circuit 36 controls the switching of the changeover switches 16, 17 and the switch 28, and the output from the output end b controls the switching of the changeover switch 19. In this case, when the changeover switches 16 and 19 are supplied with the H level, their common terminals 16c and 19c are switched to the first fixed terminals 16a and 19a, and the L
When the level is supplied to the common terminal 16c, 1
Assuming that 9c is switch-connected to the second fixed terminals 16b and 19b, the switching states of each changeover switch 16, 17, 19 and switch 28 in response to the select signal SEL are as shown in the following table.

〔Effect of the invention〕

Therefore, as described in detail above, according to the present invention, it is possible to provide an extremely good servo circuit for a disc playback device that can reduce the number of pins when integrated into a circuit.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing an embodiment of a servo circuit of a disc playback device according to the present invention;
FIG. 2 is a block circuit configuration diagram showing details of the main parts of the same embodiment, and FIG. 3 is a block circuit configuration diagram showing conventional servo means. DESCRIPTION OF SYMBOLS 11... Main light receiving part, 12, 13... Current voltage conversion circuit, 14... Subtraction circuit, 15... Addition circuit, 16, 1
7... Selector switch, 18... RF ripple signal generation circuit, 19... Selector switch, 20, 21... Sub light receiving section, 22, 23... Current voltage conversion circuit, 24... Subtraction circuit, 25... Addition circuit, 26... Operational amplifier, 27
...Output circuit, 28...Switch, 29...Focus signal generation circuit, 30...Signal processing circuit, 31...Buffer circuit, 32, 33...Amplification circuit, 34, 35...
Buffer circuit, 36...3 state detection circuit, 3
7, 38...Level comparator.

Claims (1)

[Scope of Claims] 1. A disc playback device that optically reads an information signal from a disc on which the information signal is recorded, comprising: a first signal having information corresponding to a track jump on the disc; and a first signal having information corresponding to a track jump on the disc; a first switching means for selectively guiding a second signal having information corresponding to the focus error signal; a second switching means for selectively guiding the focus error signal and the tracking error signal; and a focus search state. a third switching means for selectively switching the focus servo state; and generating a servo control signal based on each signal derived by the first and second switching means; a signal processing means for generating a selection signal that assumes a first to a third electrical state in order to control switching of the switching means; a first switching means controlling the first switching means to select the second signal in the third electrical state and select the first signal in the third electrical state;
switching signal and the selection signal respectively select a focus error signal and a focus search state in a first electrical state, and select a tracking error signal and a focus servo state in a second and third electrical state. a servo circuit for a disc playback device, comprising a switching signal generating means for generating a second switching signal for controlling the switching of both the second and third switching means so as to select each of the second and third switching means. .