Pre-engraved information carrier and optical read device therefor.

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an apparatus that reads data stored in a predetermined area on the surface of an information medium.

【0002】

[Conventional technology]

For quick and easy access to the data area, this type of information medium may have the form of a disk with reference planes divided into a plurality of track elements at regular intervals. These track elements are formed, for example, to match the winding of a constant pitch spiral centered in the center of the centering orifice. This data area is further divided into a plurality of sectors in the angular direction, and these sectors can be further subdivided into a plurality of blocks. This block is for storing data and addresses that are indispensable for addressing track elements and sectors. Dividing the data area into radial and angular directions in this way allows the read / write heads to follow the track elements regularly or to quickly jump (skip) the spacing between any two track elements. By moving in the radial direction with respect to the reference plane of the disk, data transfer can be operated extremely flexibly. The choice of sector or data block depends on the rotation of the disk, which rotation is usually fast enough to get a high data rate. A format is given to the reference plane of the disc to specifically indicate a particular track element and these track element portions devoted to data storage. That is, a pre-recorded mark is arranged so as to be inserted between the data areas. Despite the eccentricity of the disc, the light spots will be accurately centered on the track axis by taking advantage of the repeatability of these reference marks. Some of the reference marks are specifically composed of pre-record patterns for synchronizing the clocks that control the serial arrangement of the data with other reference marks scanned by the light spot.

【0003】

The reference plane of the optical memory changes its optical characteristics at the position of the pre-record pattern, and this change is detected by extremely thin light spots. Therefore, tracking errors and synchronization losses that require compensation can be easily detected by optical scanning the disc. Although data writing also causes other changes in optical properties, measures are taken to prevent such data writing or post-recording from affecting the pre-recording patterns required for tracking and clock synchronization.

【0004】

The use of optical memory, such as an optical disc given a pre-recording pattern, optically interacts with means of projecting as small a light spot as possible onto a reference plane of the disk and means of moving the light spot radially. Further, an optical reading device provided with a photodetector means for detecting the radiation returned from the irradiation region of the reference plane and a means for transmitting the rotational motion to the disk is required. When using an optical disc having a high information density, it is indispensable to be able to perform automatic spot focus and radial servo control of the spot position.

【0005】

It is also necessary to be able to change the intensity of the light spots in order to cause erasable or non-erasable optical characteristic changes in the data area that represent useful information in order to write information on the disk. ..

【0006】

In the case of an optical disc with a pitch between tracks of about 2 microns, if reading is performed using a spot with a diameter of about 1 micron, a tracking technique by sampling a pre-record pattern eccentric with respect to the track axis. Can be used. The circuit that performs the radial servo control of the spot position is configured to compare two samples of the detected signals corresponding to a pair of eccentric patterns. The configuration in this case is selected so that the radial offset (bias) of the second scan pattern with respect to the first scanned pattern is the same for each pattern pair in which it is detected.

【0007】

[Problems to be Solved by the Invention]

When the disc is subdivided into blocks and sectors in the angular direction along the radius, the eccentric patterns are aligned radially at the same pitch as the pitch of the track element. In order to increase the information density of the optical disc, the pitch of the track must be reduced. The track pitch can be much smaller than the 2 microns mentioned above without problems in reading the data accurately, but in that case there is a problem in detecting tracking errors. The cause of the radial resolution deficiency may be the mutual approach of the pre-record patterns. This is because these patterns overlap more with the reading light spot when eccentric.

【0008】

[Means for solving problems]

In order to eliminate this drawback, the present invention proposes to reverse the offset order of the pre-record pattern for each revolution or for each portion of one revolution. When reading such a disc, a suitable conversion circuit may be used to compensate for the offset reversal.

【0009】

Specifically, according to the present invention, an information medium comprising a reference plane having adjacent track elements preformatted with reference marks, each forming a continuous spiral turn and containing an offset pre-record pattern. Therefore, the equidistant scanning lines of the track element are divided into a plurality of equivalent parts by forming an intersecting portion by a plurality of orthogonal lines, and at least one and at most two of the pre-record patterns are formed at each intersecting portion. Are associated with each other so that the pre-record patterns that are contiguous on one track element are positive or negative with respect to the scan line such that at least one half-wave sequence is indicated by the edge of the pattern along each track element. The symbols representing are having equal offsets that are opposite to each other, and the pattern of one track element is the pattern of adjacent track elements with respect to the midline between the corresponding scan lines of the adjacent track elements. After interacting with the medium at the portion of the reference plane illuminated by the reading spot, the medium is marked to detect passage from one track to the next. By scanning the light detecting means for detecting the read radiation beam, the means for laterally moving the spot with respect to the adjacent track element in the reference plane, and the pre-record pattern indicating the track element. The sampling servo control means is provided with a sampling servo control means for making the spot follow the scanning line of the track element, and the sampling servo control means is connected to a conversion means that operates every time the passage is detected during the reading of the mark. An information reader characterized by being present.

【0010】

【0011】

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings with reference to non-limiting specific examples.

【0012】

BEST MODE FOR CARRYING OUT THE INVENTION

In the following description, the case where an optical disk is used as an information medium is taken as an example, but the present invention can be applied to other forms of media such as cards, tapes, drums, and the like.

【0013】

The reference mark on the reference plane is distinguished from the surrounding surface by changes in optical properties such as reflectance, and such changes can be obtained by various methods. As an example, these reference marks are either pre-recorded by pressing the reference plane against a master with suitable surface irregularities (similar to normal audio disc manufacturing), or between the write beam and the initial blank surface of the information medium. It is obtained as a result of the optical interaction of. In any case, the point is to pre-record the mark on the medium to specify the layout or format of the track.

【0014】

The data is stored in the reference plane of the optical disk as shown in FIG. 4, which is a front view of the optical disc 83. The reference plane is divided into a plurality of sectors in the angular direction by a plurality of radial lines (radiation) 67, 69, 70, 71 and 72 concentrated in the center M. As shown in FIG. 4, the sector between the radii 71 and 72 is further subdivided into a plurality of equivalent parts, and data blocks are stored in these parts. In this specific example, both the number of sectors and the number of blocks per sector are odd, so an odd number of blocks can be obtained for each full rotation of the disk. Of course, in some cases, an even number of blocks may be obtained for each rotation.

【0015】

The data is stored along the track of the optical disc. In FIG. 4, this track is represented by a scanning line 68 indicated by a chain line, which, as a non-limiting example, has the shape of a spiral with a constant pitch centered on M. The track is therefore composed of a grid of multiple evenly spaced elements, each representing a complete turn. FIG. 4 shows three windings with start and end points at a radius of 67. In order to clarify the series of data blocks along the track, the axis of the track is graduated with a number from 0 to 45 at the heading of each block. There is an inter-track gap between two adjacent (and contiguous) track elements, as shown by the dotted line 73 in FIG. The data area extends between two fast-paced scales, eg scales 9 and 10. There is another data area similar to the data area between the scales 24 and 25.

【0016】

The data area adjacent to the first mentioned data area may be a data area extending between two other scales on the same winding. The data area is not directly continuous either radially or along the track. This is because each scale is provided with a specific area containing a pre-record pattern that marks the track format.

【0017】

FIG. 1 shows a part of the contents of the specific area. In this figure, each of the scan lines 58, 59, 60 consisting of three consecutive windings has the end 50 of the adjacent data area centered and sandwiching a specific area (on the left and right in this figure). The terminal 50 is composed of, for example, a pre-recorded groove-shaped pattern separated by the specific region. In the embodiment of FIG. 1, the track element is narrower than the intertrack gap, so when the track is optically read using the light spot 53, the track appears darker than the intertrack gap. This is because the track diffracts more light. The radial lines 67, 69, 70, 71 and 72 are orthogonal to the scan line grid and the scan lines are evenly spaced from each other.

【0018】

In the center of FIG. 1, pre-record patterns 51 and 52 used to detect tracking errors for the spot with respect to the track axis are shown. These patterns are combined with other patterns (not shown) to form sector or data block headings.

【0019】

Patterns 51 and 52 constitute a half-wave train of two half-waves, equivalent and opposite to the track axis so that these patterns interact with the centered spot 53 in the same direction. Is offset to. The lower part of FIG. 1 shows the read signal S (t) transmitted by the optical sensor that senses the radiation caused by the interaction between the read spot and the pattern region as a function of time t. The solid curve 61 relates to a spot that scans the track without tracking errors.

【0020】

As is clear from this graph, the signal S (t) rises as the spot portion illuminating the periphery of the pattern becomes wider. Therefore, the detected levels are higher when scanning patterns 51 and 52 because they are offset with respect to the axis of the track, and even more when the spot passes over a completely blank or unrecorded area of the disc. It gets higher.

【0021】

The dotted lines 54 and 56 showing the outline of the spot correspond to the various scanning steps of the scanning line 59 such that the spot is offset toward the scanning line 58. In this case, the signal S (t) causes a level change as shown by the dotted line at the bottom of FIG. This level rises in parts 62 and 64. This is because the covered portion of patterns 50 and 52 due to the spot becomes smaller. Conversely, the level drops at part 63. This is because the spots are offset in the same direction as pattern 51. Sampling levels 63 and 64 and subtracting the sampled values gives a continuous tracking error signal. Dotted lines 55 and 57 represent spots offset in opposite directions with respect to scanning line 60. Therefore, an error signal with the opposite symbol occurs, in which case level 63 is higher than level 64. In one variant of the prior art not shown in FIG. 1, only one of the patterns 51 and 52 is given in any particular region, and the other is given in a particular region immediately before and after.

【0022】

The configuration of FIG. 1 gives satisfactory results if the spacing between the fast scan lines 58, 59 and 60 is relatively large relative to the diameter of the read spot. In fact, it's okay if the spots are small enough so that they don't overlap two adjacent patterns 51 or 52 that have the same spacing as the centered pattern 50. This is not the case if the pitch is made smaller and the eccentric patterns are arranged in the same way.

【0023】

Figure 2 shows the state when the track density is 1.5 times that of Figure 1. The diameter 66 of the spot 53 represents, for example, the width at half the height of the response curve 65 to the intensity of light received on the surface of the information medium. Spot 53 can still read the data written along pattern 50, but interactions with patterns 51 and 52 can lead to misdetection of tracking errors. The spot overlaps the two patterns 52 at offset position 56, and overlaps the two patterns 51 at offset position 55. As a result, levels 63 and 64 in Figure 1 do not show enough difference for accurate tracking. This loss of cross-sectional readability appears before the level of crosstalk between adjacent data tracks prevents proper reading of the data as long as the spot is accurately centered.

【0024】

It is proposed to change the distribution of pre-record patterns used to detect tracking errors in order to improve cross-directional readability within the particular region.

【0025】

FIG. 3 shows a specific example of the pattern distribution method in a plan view. The track pitch and the size of the read spot are basically the same as in FIG. 2, but the transverse distribution of the pre-record patterns 51 and 52 is not regular.

【0026】

The pre-record patterns 51 and 52 are offset with respect to the track axis by the same absolute amount as in FIGS. 1 and 2, but the order of the offset symbols is exchanged for each track element.

【0027】

In FIG. 4, the gap between tracks is shown by the dotted line 73. Pre-record patterns distributed in the same manner as in FIG. 3 are also shown in the vicinity of radial lines 67, 69, 70, 71 and 72. If the outward offset towards the edge of the disc is represented by a positive symbol, the offset order is plus-minus on windings that start at scale 0 and end at scale 15. The offset order for windings starting at scale 15 and ending at scale 30 is minus-plus and returns to its original form when crossing radius 67 again. In the case of data blocks after a pair of pre-record patterns 51 and 52 offset in opposite directions, the number of data blocks per rotation can be arbitrary, but the tracking error signal is extracted by sampling the pre-record patterns 51 and 52. In order to do so, it is necessary to consider the order reversal that occurs every time the reference radius 57 is passed. The offset order can be reversed many times, for example, once every reference radius 67,69,70,71 and 72.

【0028】

In the case of a data block after a single pre-record pattern that is offset alternately in the positive and negative directions, each orbit or track element may contain an even or odd number of patterns. In the case of an odd number, the desired pattern distribution can be obtained without alternately changing the offset along the track. However, in the case of an even number, the offset symbol must be changed at least once every one lap. To better understand the pattern distribution in the latter case, it can be assumed that patterns 51 and 52 in FIG. 3 are separated by the data block 50.

【0029】

FIG. 5 also shows an example of the pattern configuration. This is a specific example in which the patterns 51 and 52 are offset so that they are completely located within the inter-track gap. The pattern density is one half because the offset is equal to one half of the track pitch. Any arrangement in between FIGS. 3 and 5 can also be used.

【0030】

For the formation of the pre-record pattern, a photosensitive resin irradiated by a luminous flux having spots that form a latent image during a single pass is used. The image produces a pattern of constant width W.

【0031】

The pattern is offset by moving the spot perpendicular to the scan line. However, if the track element pitch is small and offset inversion is performed by the method described above, the pre-record pattern may have a polymerized shape due to two continuous irradiations. Figure 11 shows various situations that can actually occur. The offset of the pattern involves two magnitudes, especially the gap ε between the edge of the pattern and the scan line, and the offset E between the axis of the pattern and the scan line caused by a single irradiation.

【0032】

FIG. 11a shows two scan lines 100 and 101 and a pattern provided by two irradiations on elongated zones 102 and 103 with a width of W. The axis 105 of the zone 102 is offset by E with respect to the scan line 100, and the axis 106 of the zone 103 is offset in the same opposite direction with respect to the scan line 101.

【0033】

The edge 107 of the zone 102 is separated from the line 100 by a gap ε, and there is a gap of the same number of inverse symbols between the edge 108 of the zone 103 and the line 101. If the gap ε and the offset E have a positive symbol and the edge 107 and the axis 106 are on the same side with respect to the axis 100, the above quantities satisfy the algebraic relation E-ε = W / 2. .. W / 2 is a positive number. The symbol for the gap ε can be inverted because edge 107 can also be located on the opposite side (see Figure 11d). As a result, the 0-value offset E has the characteristic of ε = -W / 2. This particular ε value is excluded when writing the offset pattern.

【0034】

FIG. 11a shows the contour 104 of the read spot offset with respect to scan line 100. For better understanding, this positive offset can be, for example, equal to ε. This means that half of the spots interact with the resulting pattern and only edge 107 is involved in this interaction.

【0035】

Therefore, the only parameter of the pattern that affects the detection of tracking errors is the gap ε. This gap must be different from the value -W / 2, but can be positive, negative or 0.

【0036】

If the pitch is p as shown in FIG. 11a, the obtained pattern accurately shows the offset E through the gap ε obtained from the relational expression ε = EW / 2. When the pitch p is reduced by the amount Δp, a single pattern 109 showing the interaction of the zones 102 and 103 with the spot 104 so that they completely overlap each other and as a result are not affected by the change in pitch, as in the specific example of FIG. 11b. Is obtained. However, the minimum pitch value that can be tolerated in the formation of the pre-record pattern is a value p-Δp equal to W + 2ε. For example, when the pitch is reduced to a value p-α smaller than W + 2ε as shown in FIG. 11c, the obtained pattern has a shape in which the outer edge is no longer separated from the scanning lines 100 and 101. In this case, a new gap ε'depending on the pitch value is created, which is a drawback.

【0037】

However, the drawbacks of the pattern as shown in FIG. 11c are only due to the formation method. If the zones 102 and 103 that formed this pattern had a new gap (substantially equal to 0) that was different from the gap ε, then the state of FIG. 11a or FIG. 11b was obtained.

【0038】

From the above, it can be concluded that the offset of the polymerization pattern is particularly related to the gap in the pitch range that allows the reproduction of the gap between the pattern and the scan line. The pattern is arranged symmetrically with respect to the median line between scan lines 100 and 101. Also, the 0 gap ε does not mean that the offset is 0, but the gap ε = -W / 2 indicates the absence of the offset. FIG. 11d shows an example of a pattern in which the gap ε has the opposite symbol to that in FIG. 11a and the pitch can be significantly reduced. Increasing the pitch of the track elements avoids polymerization of irradiation zones 102 and 103, resulting in a change in composition from one pattern to two patterns, which does not affect the gap ε.

【0039】

However, it is also possible to form a pre-record pattern that simultaneously contains at least one offset portion and at least one centered portion located at the edge of the pattern. The presence of centered edges causes a transition of the read signal when scanning the pre-record pattern. These signals will generate synchronous signals after proper processing. These signals are sent only when scanning a pre-record pattern symbolized for that purpose.

【0040】

FIG. 6 shows the shape of the dual purpose pre-record pattern. The unit pattern on the top side is shown on the left and the unit pattern on the bottom side is shown on the right side of this figure. The pattern in this case has a substantially uniform width, but the central portion is offset with respect to the scan line (dotted line) while the edges are centered. According to the offset inversion rule described above, the unit patterns are joined to each other as shown in FIG. 6, and as a result, they have an elongated X-ray shape.

【0041】

FIG. 7 shows a similar, but maximally polymerized pre-record pattern. As is apparent from the configurations of FIGS. 3, 5, 6 and 7, positive and negative offsets are provided on the track element according to a predetermined order, which orders are reversed with respect to the two adjacent track elements. To. This order reversal or conversion must be reflected in the circuit that detects the tracking error.

【0042】

Therefore, it is usually necessary to specify the scanning phase corresponding to the current order conversion on the information medium. In the information medium of FIG. 4, a radius of 67 marks the connection of track elements.

【0043】

Figure 8 shows the beginning of a sector that records several blocks of data at regular intervals. Scanning from left to right on a portion of the epicycle along the track element, eg, this sector extending over 1/32 epicycle, provides specific regions 77 at regular intervals. These specific areas include pre-record patterns for synchronization and tracking. Each region 77 typically has a length A equal to eight times the size of a 1-bit cell and is separated from the immediate neighbor by an intermediate region that can contain 96 bit cells. In this way, each zone b1, b2, b3 constitutes a group consisting of 104 cells. The sector heading H is composed of the first group b1 including the area 79 used for addressing the memory zone. Area 79 contains the addresses of the sectors represented by three 24-bit words. The intermediate region 78 may include, for example, a symbol indicating an order change performed at each epicycle. In this case, the remaining areas 80, 81 and later are used for data storage. For example, length B can correspond to 24 bits, region 79 can have 72 bits of length C, and each data region can have 96 bits of length D.

【0044】

The reading of the information medium as described above cannot be performed without modifying the circuit so that the light spot follows the track element or skips a plurality of tracks.

【0045】

FIG. 9 shows a first specific example of the optical reader of the present invention.

【0046】

The information medium 83 is supported by a rotary spindle that has an axis M and is driven, for example, at a constant rotational speed. The reference plane of the information medium 83 is irradiated by the laser source 85 via the translucent blade 86, the rotating mirror, and the focusing lens 84. The rotating mirror is rotated by the motor 88 in order to move the light spot formed on the reference plane of the medium 83 by the lens 84. This movement is performed in the transverse direction with respect to the scanning line of the track element. The light interacting with the information medium is sent to the light sensing means via the objective lens 84, the rotating mirror and the blade 86, which sends an electrical reading signal containing various information that is sequentially read according to each track element. To do.

【0047】

This electrical signal is also sent to the sampling window generator 93, a circuit 94 that evaluates the spot offset with respect to the scan line, and, if necessary, a circuit 92 that identifies a specific mark for order conversion. The control circuit 91 operates the motor 88 according to two inputs (quantities), that is, a tracking error to be compensated for and a track skip width to be executed. The width of the track skip is measured by a control circuit 90 that can control disk access and operate access motors (not shown in FIG. 9) in response to external read or write requests. The quantity representing the tracking error is obtained by the circuit 94 without considering the order change of the pre-record pattern given for that purpose. Therefore, the symbol of the signal transmitted by the evaluation circuit 94 must be changed as necessary. To this end, the present invention inserts a conversion circuit 89 between circuits 91 and 93 to give appropriate symbols to the tracking error signal in order to accurately operate the servo control loop that compensates for the tracking error. The conversion circuit 89 shown in FIG. 9 has two stages connected in a cascade to convert the connection between the input terminal and the output terminal according to two different controls. One of the above two controls is given by the circuit 90 when performing a track skip corresponding to an odd number of pitches. The other control is given by the identification circuit 92 when scanning the order conversion mark present in one of the regions 78.

【0048】

If the track skip matches the detection of this mark, both of the above steps are converted, resulting in the error symbol changing twice and thus returning to the original connection state.

【0049】

As a modification, the information medium 83 may be provided with a reference track on which a pre-record mark is formed for synchronizing the medium passing through the reading head with the reading device. Such synchronization is necessary to read the various regions (79,80,81) at the correct timing. In this case, the ring may have a specific mark relating to the order conversion of the pre-record mark located in the annular region where the information is stored. The ring is scanned by an auxiliary optical head 95 that sends out a specific read signal associated with the rotation of the disk. As shown by the dotted line in FIG. 9, this read signal replaces the read signal from the detection circuit 87 as an input to circuit 92. In this case, zone 78 in FIG. 8 may include a specific signal indicating a sector address scan.

【0050】

In FIG. 9, the conversion circuit 89 is shown outside the circuit 94 that measures the spot offset signal by comparing two read signal samples taken during scanning of the offset portion of the prerecord pattern. These samples may be converted at the input of the comparison circuit as shown in FIG. In this case, the circuit 84 is included in the rectangular enclosure 94, but the elements outside it are the same as in FIG.

【0051】

The spot offset evaluation circuit 94 has two similar gates 96 and 97, which receive the read signal sent by the detection circuit 87. Each gate is controlled by a sampling pulse from the generator 93, but the sample obtained at the output of gate 96 is said to ensure that it represents the interaction between the spot and the pre-record pattern with the predetermined offset symbol. The two pulses are sent to gates 96 and 97 after being converted by circuit 89. The same is true for the other gate and the other offset symbol, so the comparison circuit 98 always supplies the spot offset value of the appropriate symbol. This value is stored or smoothed by circuit 99 before being sent to control circuit 91. The conversion circuit 89 is controlled as described above and can also be incorporated into the generator 93.

【0052】

The readers of FIGS. 9 and 10 can also be adapted to read information media using pre-record marks, all arranged in the same order. For that purpose, it is only necessary to keep the conversion circuit 89 in a preselected state. The circuit 92 that detects the mark indicating that the order has been changed can easily recognize the scanning mode to be executed in cooperation with the timing circuit.

【0053】

In the configurations of FIGS. 6 and 7, two X-shaped patterns adjacent to each other may be brought close to each other so that their ends are in contact with each other to form a continuous pattern. In the case of FIGS. 6 and 7, the fact that the spot has passed through the two pre-record patterns is detected by the transition of the four signal states generated at the four ends of the two pre-record patterns. In this case, since there are only two state transitions of the signal, the state transitions of a total of four signals should be obtained by using the two state transitions that occur at the ends of the two opposing patterns 50 in the data area. Can be done. Instead of this, the shapes of the pre-record patterns may be such that when they are in contact with each other, when a spot passes through them, four signal state transitions occur.

【0054】

When considering the track element address read from the medium, it is not necessary to provide any particular means of reordering. For example, if two consecutive track elements have the numbers n + 1 and n as addresses, then the parity change can be used to select the appropriate conversion. In this case, the circuit 92 of FIGS. 9 and 10 is used to measure the parity of the track element address and indicate the parity change that occurs with each revolution. For example, the address of a sector can also be used by detecting a change from the last sector of one track element to the first sector of the next track element and performing a reorder when dealing with the first sector.

[Simple explanation of drawings]

[Figure 1]

An explanatory diagram showing a conventional pre-record pattern arrangement method and a waveform diagram of a corresponding read signal.

[Figure 2]

Explanatory drawing similar to FIG.

[Fig. 3]

The explanatory view which shows an example of the pre-record pattern arrangement method which concerns on this invention.

[Fig. 4]

The plan view of the optical disk which concerns on this invention.

[Fig. 5]

Explanatory drawing which shows one modification of the pre-record pattern.

[Fig. 6]

Explanatory drawing of another modification which also has a pattern for synchronizing the phase of a clock.

[Fig. 7]

An explanatory diagram of a pattern shape that is more compact than FIG.

[Fig. 8]

The explanatory view which shows an example of the sector heading of the optical disk which has a pre-record mark.

[Fig. 9]

The schematic explanatory view of the reading apparatus of this invention.

[Fig. 10]

FIG. 6 is a simplified explanatory view of another reading device of the present invention.

[Fig. 11]

It is a simplified explanatory drawing which shows various states.

[Explanation of symbols]

83 optical disc 51,52,74,75,76 Pre-record pattern 53,54,55,56,57 Light spot 73 Gap between tracks 84 Condenser lens 85 laser source 86 translucent blade 87 Light sensing means 88 motor 89 Conversion circuit 90,91 control circuit 92 Identification circuit 93 Sampling window generator 94 Evaluation circuit 95 Auxiliary optical head 96,97 Gate 98 Comparison circuit