Crosstalk canceler with digital filter for producing pseudo crosstalk component

A crosstalk canceler cancels crosstalk components mixed into a reproduced signal of a target track from a first and a second neighboring tracks positioned on both sides of the target track formed on an optical disc. The crosstalk canceler includes: unit for reproducing a signal recorded on the tracks of the optical disc; unit for processing the reproduced signal to produce 1-bit binary data indicating data recorded on the first neighboring track and outputting first binary data; unit for producing a first pseudo crosstalk component which mixes into the reproduced signal of the target track from the first neighboring track based on the first binary data; unit for delaying an output signal corresponding to a pure recorded signal of the track preceding the target track to produce second binary data indicating data recorded on the second neighboring track and outputting second binary data; unit for producing a second pseudo crosstalk component which mixes into the reproduced signal of the target track from the second neighboring track based on the second binary data; and unit for subtracting the first and the second pseudo crosstalk components from the reproduced signal of the target track and outputting a pure recorded signal of the target track.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
This invention relates to a crosstalk canceler, and more particularly to a 
crosstalk canceler for eliminating crosstalk between neighboring tracks of 
a high recording density type optical disc utilizing digital signal 
processing. 
2. Description of the Prior Art 
When the track pitch of the optical disc is reduced so as to increase the 
recording density thereof, the light spot irradiated on the target track 
covers the neighboring tracks, and thereby the crosstalk is generated and 
mixed into the read-out signal of the target track. In order to overcome 
this problem, there has been known a crosstalk cancelling technique in 
which a pseudo crosstalk component is electrically produced and is 
subtracted from the read-out signal of the target track to obtain the pure 
signal recorded on the target track. However, such a crosstalk canceler 
generally requires a complicated and large-scaled circuitry for the 
production of the pseudo crosstalk component. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a crosstalk canceler 
capable of accomplishing satisfactory crosstalk cancelling performance 
with a simplified circuitry. 
According to one aspect of the present invention, there is provided a 
crosstalk canceler for cancelling crosstalk components mixed into a target 
track from a first and a second neighboring tracks positioned on both 
sides of the target track formed on an optical disc. The crosstalk 
canceler includes: reproducing unit for reproducing a signal recorded on 
the track of the optical disc; processing unit for processing the 
reproduced signal to produce 1-bit binary data indicating data recorded on 
the first neighboring track and outputting first binary data; first 
crosstalk detecting unit for producing a first pseudo crosstalk component 
which mixes into the target track from the first neighboring track based 
on the first binary data; delay unit for delaying the first binary data to 
produce second binary data indicating data recorded on the second 
neighboring track and outputting second binary data; second crosstalk 
detecting unit for producing a second pseudo crosstalk component which 
mixes into the target track from the second neighboring track based on the 
second binary data; and subtracting unit for subtracting the first and the 
second pseudo crosstalk components from the reproduced signal of the 
target track and outputting a pure recorded signal of the target track. 
In accordance with the crosstalk canceler thus configured, the signal of 
the target track reproduced from the optical disc is supplied to the 
subtracter. The processing unit produces a 1-bit binary data of the first 
neighboring track from the reproduced signal, and the delay unit produces 
a 1-bit binary data of the second neighboring track from the 1-bit binary 
data of the first neighboring track. The first crosstalk detecting unit 
produces the first pseudo crosstalk component which indicates crosstalk 
from the first neighboring track to the target track. Similarly, the 
second crosstalk detecting unit produces the second pseudo crosstalk 
component which indicates crosstalk from the second neighboring track to 
the target track. The subtracting unit subtracts the first and the second 
pseudo crosstalk components from the reproduced signal of the target 
track. As a result, the crosstalk components are eliminated and the pure 
recorded signal of the target track is obtained. 
According to another aspect of the present invention, there is provided a 
crosstalk canceler for cancelling crosstalk components mixed into a target 
track from a first and a second neighboring tracks positioned on both 
sides of the target track formed on an optical disc. The crosstalk 
canceler includes: reproducing unit for reproducing a signal recorded on 
the track of the optical disc; processing unit for processing the 
reproduced signal to produce 1-bit binary data indicating data recorded on 
the first neighboring track and outputting first binary data; first 
crosstalk detecting unit for producing a first pseudo crosstalk component 
which mixes into the target track from the first neighboring track based 
on the first binary data; delay unit for delaying a pure recorded signal 
of the target track to produce second binary data indicating data recorded 
on the second neighboring track and outputting second binary data; second 
crosstalk detecting unit for producing a second pseudo crosstalk component 
which mixes into the target track from the second neighboring track based 
on the second binary data; and subtracting unit for subtracting the first 
and the second pseudo crosstalk components from the reproduced signal of 
the target track and outputting the pure recorded signal of the target 
track. 
In accordance with the crosstalk canceler thus configured, the signal of 
the target track reproduced from the optical disc is supplied to the 
subtracter. The processing unit produces a 1-bit binary data of the first 
neighboring track from the reproduced signal, and the delay unit produces 
a 1-bit binary data of the second neighboring track from pure recorded 
signal of the target track outputted by the subtracting unit. The first 
crosstalk detecting unit produces the first pseudo crosstalk component 
which indicates crosstalk from the first neighboring track to the target 
track. Similarly, the second crosstalk detecting unit produces the second 
pseudo crosstalk component which indicates crosstalk from the second 
neighboring track to the target track. The subtracting unit subtracts the 
first and the second pseudo crosstalk components from the reproduced 
signal of the target track. As a result, the crosstalk components are 
eliminated and the pure recorded signal of the target track is obtained. 
The nature, utility, and further features of this invention will be more 
clearly apparent from the following detailed description with respect to 
preferred embodiments of the invention when read in conjunction with the 
accompanying drawings briefly described below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Description of Typical Crosstalk Canceler 
For a full understanding of the nature and utility of the present 
invention, a brief consideration of a typical crosstalk canceler will be 
first presented below with reference to FIGS. 1A and 1B. FIG. 1A 
illustrates a configuration of a typical crosstalk canceler. As shown, the 
light spot LB covers not only the target track but also the neighboring 
tracks positioned on both inner and outer sides of the target track with 
respect to the radial direction of the optical disc 51, and therefore the 
crosstalk is generated by the light beam reflected by the neighboring 
tracks. The photodetector 52 converts the light beam reflected by the 
optical disc 51 into an electric signal, and the A/D converter 53 converts 
the electric signal into digital data representative of the magnitude of 
the electric signal recorded on the track. The signal outputted by the A/D 
converter 53 is referred to as recorded data Y.sub.a of the track Ta. The 
8-bit memory 54 gives the digital data a delay time corresponding to a 
time period required for reproducing one track of the optical disc 
(hereinafter referred to as "delay time of one-track", and outputs the 
delayed data x.sub.b as recorded data of the track Tb. The 8-bit memory 40 
further gives a delay time of one-track to the recorded data x.sub.b to 
produce recorded data y.sub.c of the track Tc. Recorded data y.sub.c is 
supplied to the filter 41 which filters recorded data y.sub.c to produce 
the pseudo crosstalk component CT.sub.c. Similarly, recorded data Y.sub.a 
is supplied to the filter 42 which filters recorded data y.sub.a to 
produce the pseudo crosstalk component CT.sub.a. FIG. 1B illustrates a 
configuration of the filter 41 or 42. The subtracter 44 subtracts the 
pseudo crosstalk components CT.sub.a and CT.sub.c from recorded data 
x.sub.b to output a pure recorded data S of the track Tb from which 
crosstalk components are eliminated. The Viterbi decoder 43 decodes the 
data S for correcting bit errors or the like. 
In the above described crosstalk canceler, recorded data is processed in a 
form of 8-bits data by the parallel data processing. Accordingly, the 
delay elements 45 and 46 and the multiplier 47-49 should be designed to 
perform multi-bit data processing. However, multiplication of multi-bit 
data requires many adders. When the number of the coefficients is 
increased, large number of arithmetic elements are required for the pseudo 
crosstalk component calculation. In addition, memories for delaying 
recorded data is needed to have large capacity. In this view, the circuit 
scale should be necessarily enlarged. 
Next, preferred embodiments of the present invention will be described 
below with reference to the accompanying drawings. The following 
description relates to the cases where the present invention is applied to 
an optical disc reproduction apparatus employing a single laser beam. 
1st Embodiment 
FIG. 2 illustrates a configuration of a crosstalk canceler according to the 
first embodiment of the present invention. The crosstalk canceler 100 
eliminates the crosstalk from the signal read out from the optical disc 1. 
The optical disc 1 is formed with a single track spirally formed (each 
turns of the spiral track will be hereinafter referred to simply as 
"track"), and the laser beam is irradiated on the surface of the optical 
disc 1 by the laser beam source (not shown) so as to form the light spot 
LB thereon. The photodetector 2 converts the light beam reflected by the 
optical disc 1 into an electric read-out signal which is an RF signal. The 
A/D converter 3 converts the RF signal into a digital read-out signal, 
e.g., 8-bits parallel data representative of the magnitude of the RF 
signal, by the A/D conversion. The 8-bits memory 4, which may be of FIFO 
type, stores the read-out data for the capacity of digital data recorded 
on one track. The 8-bits memory 4 gives a delay time of one-track, i.e., 
required for the reproduction of one track to the read-out data, and 
supplies the delayed read-out data to the subtracter 5 as the recorded 
data x.sub.b of the track Tb. The Viterbi decoder 6 applies the Viterbi 
decoding to the data X.sub.2 to produce a 1-bit data y.sub.a. The filter 7 
filters the 1-bit data y.sub.a to produce a pseudo crosstalk component 
CT.sub.a of the track Ta. Each of the 1-bit memories 8 and 9 delays the 
1-bit data y.sub.a by the delay time of one-track, respectively, to 
produce the 1-bit data y.sub.c. The filter 10 filters the 1-bit data 
y.sub.c to produce a pseudo crosstalk component CT.sub.c. The subtracter 5 
subtracts the pseudo crosstalk components CT.sub.a and CT.sub.c from the 
data X.sub.b. The Viterbi decoder 11 converts the data S from which 
crosstalk components are eliminated into a 1-bit data X.sub.3 and outputs 
it. 
Next, the operation of the crosstalk canceler 100 will be described in more 
detail. When tracing the track Ta, the light spot LB covers the target 
track Ta, but the inner and outer edges of the light spot LB also cover 
the neighboring tracks, thereby the crosstalk is generated and is mixed 
into the read-out signal supplied to the photodetector 2. Therefore, the 
data x.sub.b obtained by simply A/D converting and delaying the read-out 
signal includes the crosstalk components mixed from the neighboring tracks 
Ta and Tc in addition to the recorded information of the track Tb. The 
data x.sub.2 outputted by the A/D converter 3 represents the magnitude of 
the read-out signal x.sub.1. The data x.sub.2 is supplied to the Viterbi 
decoder 6 in which Viterbi decoding is performed. The data x.sub.2 is also 
supplied to the 8-bits memory 4 to be delayed by the delay time of 
one-track and outputted as the 8-bits data x.sub.b. The 1-bit data y.sub.a 
outputted by the Viterbi decoder 6 is delayed by the 1-bit memories 8 and 
9 by the delay time of two tracks, in total, and is outputted as the 1-bit 
data y.sub.c. 
The Viterbi decoder 6 receives the 8-bits data x.sub.2 in parallel, and 
determines a 1-bit data which is assumed to be the recorded data of the 
target track Tb. Generally, digital data having a specific frequency 
characteristics is recorded on and reproduced from the optical disc. In 
many cases, the data reproduced from the optical disc may be dissimilar to 
the actual recording pattern of the recorded data due to intersymbol 
interference and affection by noise. The Viterbi decoding can overcome 
this problem because the Viterbi decoding determines data of maximum 
likelihood from the successive multi-bits read-out data inputted thereto. 
Specifically, the Viterbi decoder 6 judges whether the logical value 
represented by the 8-bits digital data is "1" or "0", and produces a 
digital data of target track with less data error possibility. The 
memories 8 and 9 may be constituted by 1-bit Dynamic RAMs or FIFO memories 
which delay the digital signal. In this way, the data y.sub.a, x.sub.b and 
y.sub.c have such an interrelation in time as the read-out data 
simultaneously obtained from three tracks at the positions aligned in a 
radial direction of the optical disc. 
FIG. 5 illustrates data processed in the crosstalk canceler shown in FIG. 
2. The 8-bits data x.sub.b includes crosstalk component, and indicates 
magnitude level of the RF signal x.sub.1. The data y.sub.a has sampled 
values of "1" or "0" which corresponds to the information recorded on the 
track Ta. The data y.sub.c represents data read out two rotation before, 
that is, the recorded data of the track Tc on the other side of the track 
Ta. The crosstalk component in the data x.sub.b is generated by the 
intermixture of the data y.sub.a and y.sub.c into the data x.sub.b of the 
track Tb. The crosstalk component therefore has strong correlation with 
the data y.sub.a and y.sub.c, and therefore pseudo crosstalk components, 
which intermixes into the data of the track Tb from the tracks Ta and Tc, 
can be produced from the data y.sub.a and y.sub.c by filtering process of 
the digital filter. The filters 7 and 10 perform this function. The filter 
for producing pseudo crosstalk component may be configured in various 
forms as described below. 
(a) Digital Filter: 
FIG. 3A illustrates a configuration of digital filter for producing the 
pseudo crosstalk component which is employed as the filters 7 and 10, and 
FIG. 3B illustrates the circuit configuration of the coefficient 
multiplier 14 shown in FIG. 3A. In FIG. 3A, the reference numerals 12 and 
13 denote delay elements, the reference numerals 14-16 denote coefficient 
multipliers and the reference numeral 17 denotes an adder. The delay 
elements 12 and 13 may be constituted by Flip-Flop circuits which operate 
binary data. The coefficient multipliers 14-16 multiply the digital data 
y.sub.a or y.sub.c by coefficients (e.g., "a" in multiplier 14) using the 
gate circuits G.sub.1 -G.sub.8 shown in FIG. 3B. By determining 
appropriate coefficients "a"-"c", the pseudo crosstalk components can be 
obtained from the digital data y.sub.a and y.sub.c. On the assumption that 
the frequency characteristics between signals of the neighboring tracks is 
stable, the filter coefficients may be fixed. In addition, an adaptive 
transversal filter may be employed in order to precisely adapt the filter 
coefficients to various types of optical discs. In such a case, the filter 
coefficients are calculated from the digital data read out from the target 
track and the neighboring tracks. Specifically, when the transversal 
filter is applied to this embodiment, an operation unit for operating the 
filter coefficient is employed to calculate the filter coefficient from 
the data x.sub.b and the data of the neighboring tracks, and the 
coefficients "a"-"c" in FIG. 3B are renewed. 
The pseudo crosstalk components CT.sub.a and CT.sub.b from the tracks Ta 
and Tc thus obtained are illustrated in FIG. 5. They are 8-bits digital 
data representative of the magnitudes of the pseudo crosstalk components 
thus calculated. The subtracter 5 subtracts the pseudo crosstalk 
components CT.sub.a and CT.sub.c from the data x.sub.b which includes the 
actual crosstalk components, and outputs the data S indicative of the pure 
recorded data of the target track Tb. The Viterbi decoder 11 conducts 
Viterbi decoding onto the data S to obtain the data having maximum 
likelihood from the data S and outputs the serial data having less error 
components. It is noted that the Viterbi decoder 11 may be omitted when 
the parallel data S is directly processed by following processing units. 
(b) Filter of Partial Response system: 
The filter for producing pseudo crosstalk component may be further 
simplified when the Partial Response system is introduced to the 
recording/reproduction system. As a general knowledge, in digital data 
transmission, intersymbol interference takes place in the transmitted 
signal on the reception side, and the degree of the intersymbol 
interference increases as the transmission rate is increased. This is true 
for the digital data recording on the optical disc. Namely, as the 
recording density becomes high, the degree of the intersymbol interference 
increases. The Partial Response system utilizes the intersymbol 
interference positively. That is, in the Partial Response system, the 
recording and reproduction system is designed to have a prearranged 
interference characteristics to give the intentionally-designed 
intersymbol interference to the reproduced data. Since the characteristics 
of the intersymbol interference is thus known, it can be eliminated from 
the reproduced data by an appropriate data processing. In this way, the 
recording density of the optical disc may be improved with the aid of the 
Partial Response system. The characteristics of the intersymbol 
interference has been researched so as to adapt the system to various 
types of recording and reproduction systems. In this embodiment, Partial 
Response system PR(1,1) and PR(1,2,1) are utilized for the recording and 
reproduction system of the optical disc. PR(1,1) indicates the system in 
which the sampled data at the time t=0 gives a positive interference of 
equal magnitude to the sampled data at the time t=T. PR(1,2,1) indicates 
the system in which the sampled data at the time t=0 gives a positive 
interference of twice magnitude to the sampled data at the time t=T and a 
positive interference of equal magnitude to the sampled data at the time 
t=2T. 
FIGS. 4A and 4B illustrate the configurations of the filters for producing 
pseudo crosstalk component where the partial response system is applied to 
the recording and reproduction system. FIG. 4A is the filter for the 
system PR(1,1) and FIG. 4B is the filter for the system PR(1,2,1). As 
shown in FIG. 4A, the filter for producing the pseudo crosstalk component 
for the system PR(1,1) can be constituted by a delay element 20, 
multipliers 21 and 22 for multiplying the same coefficients and an adder 
23. In the similar manner, the filter for producing the pseudo crosstalk 
component for the system PR(1,2,1) can be constituted by a delay elements 
24 and 25, multipliers 26-28 and an adder 29, as shown in FIG. 4B. If the 
coefficients of the respective multipliers 26-29 are determined to be 
exponential value of 2 (i.e., 2.sup.n), the multipliers may be constituted 
by simple bit-shifting circuits including registers. In this examples of 
FIGS. 4A and 4B, the multipliers 21, 22 and 27 multiply the coefficient 
1/2, and the multipliers 26 and 28 multiply the coefficient 1/4. The data 
y.sub.a and y.sub.c are filtered by the filters 7 and 10, respectively. 
The subtracter 5 subtracts the pseudo crosstalk components CT.sub.a and 
CT.sub.c from the data x.sub.b which includes the actual crosstalk 
components, so as to output the pure recorded data S from which the 
crosstalk components are eliminated. 
(c) Filter utilizing look-up table: 
A filter utilizing a look-up table may also be employed as the filter for 
producing the pseudo crosstalk component. Specifically, the filters 7 and 
10 are constituted by storage devices such as ROM. Namely, the crosstalk 
components corresponding to the data outputted by the Viterbi decoder 6 
are calculated, in advance, and stored in the ROM. In storing the 
crosstalk components thus calculated in the ROM, the data outputted by 
Viterbi decoder 6 is used as the address data for storing the crosstalk 
components. When the data from the Viterbi decoder 6 is supplied to the 
filters, the crosstalk components stored therein in correspondence with 
the data, as address, is read out as the appropriate crosstalk components. 
The crosstalk components thus read out may be directly supplied to the 
subtracter 5. 
As described above, according to the first embodiment, the pseudo crosstalk 
components can be produced by a simple circuit, without employing 
multi-bits multipliers or the like, and therefore the scale of the circuit 
may be reduced. In addition, since the 1-bit memories can be used as the 
delay units to obtain the data of the neighboring tracks, total cost of 
the apparatus may be low. Further, an area occupied by the memories on the 
circuit board may be reduced and hence the whole size of the apparatus may 
be small. For example, assuming that a single track of the optical disc 
records 2M bits data, the A/D converted data become 16M bits (=2M.times.8 
bits), and hence a large capacity memory more than 16M bits must be 
employed. In contrast, according to this embodiment, one 8-bit memory and 
two 1-bit memories, about 20M bits in total, suffice the necessary storage 
capacity, and the total storage capacity may be approximately halved. This 
difference in total storage capacity becomes larger, as the recording 
capacity of a single track increases. This gives negligible affection in 
total cost because such a large capacity memory costs very high. Still 
further, since the Viterbi decoders are used to obtain the binary data of 
the neighboring tracks, bit error rate may be improved. 
2nd Embodiment 
The second embodiment described below produces the pseudo crosstalk 
components of the neighboring tracks from the recorded data of the target 
track. FIG. 6 illustrates a configuration of the crosstalk canceler 
according to the second embodiment. As shown in FIG. 6, the crosstalk 
canceler 101 eliminates the crosstalk components from the data read out 
from the optical disc 1. In FIG. 6, components identical to those shown in 
FIG. 2 are applied with the identical reference numerals and the 
description thereof will be omitted, for the sake of brevity. As seen from 
FIGS. 2 and 6, the crosstalk canceler 101 differs from the crosstalk 
canceler 100 in that the filter 10 receives the output data of the Viterbi 
decoder 11 via the 1-bit memory 30. The 1-bit memory 30 stores the 1-bit 
data x.sub.3 outputted by the Viterbi decoder 11, gives the delay time of 
one track to it and then outputs the delayed data as the 1-bit data 
y.sub.c representing the information recorded on the track Tc. 
Next, the operation of the crosstalk canceler 101 will be described. The 
data x.sub.2 is supplied to the Viterbi decoder 6 which judges the binary 
value of the 8-bits data x.sub.2 and outputs the 1-bit data y.sub.a. The 
filter 7 produces the pseudo crosstalk data CT.sub.a from the 1-bit data 
y.sub.a, and the subtracter 5 subtracts the pseudo crosstalk component 
CT.sub.a from the data x.sub.b to output the data S. The Viterbi decoder 
11 detects the magnitude of the data S and outputs the data x.sub.3 which 
has maximum likelihood for the magnitude of the data x.sub.b. The 1-bit 
memory 30 delays the data S and the filter 10 produces the pseudo 
crosstalk component CT.sub.c indicating the crosstalk components from the 
track Tc. In this way, the pseudo crosstalk components CT.sub.a and 
CT.sub.c are produced and subtracted from the data x.sub.b to output the 
binary data x.sub.3 which indicates the pure recorded data of the target 
track Tb. 
As described above, according to the second embodiment, the delay function 
to obtain the data of the neighboring tracks can be accomplished only with 
one 1-bit memory, and therefore the total storage capacity may be further 
reduced. 
3rd Embodiment 
The third embodiment aims to eliminate the intersymbol interference 
generated between the sampled data successively obtained, i.e., 
interference between successive data in the tangential direction of the 
disc, as well as the crosstalk components generated between the 
neighboring tracks in the radial direction of the disc. FIG. 7 illustrates 
the crosstalk canceler 102 according to the third embodiment. In 
comparison with the crosstalk canceler shown in FIG. 2, in the crosstalk 
canceler 102, the intersymbol interference filter 31 is provided between 
the intermediate point of the 1-bit memories 8 and 9 and the subtracter 5. 
The intersymbol interference filter 31 receives the data y.sub.b, produces 
the pseudo intersymbol interference component and supplies it to the 
subtracter 5. The other components are identical to those shown in FIG. 2, 
and hence the description thereof will be omitted. FIG. 8A illustrates the 
configuration of the intersymbol interference filter 31. The intersymbol 
interference filter 31 includes delay elements 33-36 for delaying the data 
by a predetermined delay time, respectively, multipliers 37 and 38 for 
multiplying the data by coefficients and an adder 39 for producing a 
pseudo intersymbol interference component CT.sub.i. 
Next, the operation of the crosstalk canceler 102 will be described. It is 
now assumed that the intersymbol interference class 2 (i.e., PR(1,2,1)) is 
introduced to the recording and reproduction system, and that the 
recording and reproduction system has a specific impulse response as shown 
in FIG. 8B. FIG. 8B illustrates a response of an impulse applied to the 
recording and reproduction system at the time t=0. Referring to FIG. 8B, 
only the data "b", "c" and "d" can be decoded by the Viterbi decoder and 
the magnitude of the data "a" and "e" indicate the intersymbol 
interference. The intersymbol interference deteriorates the judgement 
accuracy by the Viterbi decoding which produces the binary data. The 
output data of the 1-bit memory 8 represents the data recorded on the 
track Tb, and the intersymbol interference filter 31 produces the pseudo 
interference component from the data y.sub.b. Namely, the intersymbol 
interference filter 31 produces the pseudo interference component CT.sub.i 
corresponding to the data "a" and "e" shown in FIG. 8B from the data 
y.sub.b. The transversal filter shown in FIG. 8A has a filter response to 
output data corresponding to only data "a" and "e" in response to impulse 
signal inputted thereto. Therefore, the output CT.sub.i of the intersymbol 
interference filter 31 indicates the pseudo intersymbol interference 
between successive data recorded on the target track Tb. The subtracter 5 
subtracts the pseudo interference component CT.sub.i from the data x.sub.b 
as well as the pseudo crosstalk components CT.sub.a and CT.sub.c, thereby 
eliminating the intersymbol interference from the data x.sub.b. The 
Viterbi decoder 11 produces the data X.sub.3 from the data S from which 
crosstalk components and intersymbol interference component are 
eliminated. 
As described above, according to the third embodiment, the intersymbol 
interference generated in the track direction can be eliminated by simply 
providing the crosstalk canceler of the first embodiment with the 
intersymbol interference filter. Since the crosstalk and interference 
components in both radial and tangential directions of the disc may be 
thus eliminated, this embodiment is preferably applicable to the 
reproduction apparatus for an optical disc of high recording density type. 
The present invention may be embodied in other various specific forms. For 
example, although the data is processed in 8-bits unit in the above 
embodiments, it may be processed as 16- or 24-bits data. In a system in 
which the intersymbol interference is not so serious, the introduction of 
the Partial Response system is unnecessary. Further, when the Partial 
Response system is introduced, the system of other classes such as 
PR(1,0,-1) or PR(1,1,-1,-1) may be used. In order to obtain the binary 
data of the neighboring tracks, not only the Viterbi decoder but binary 
decoders of other types may be employed. 
As described above, according to the present invention, the pseudo 
crosstalk component can be calculated by a simple circuit. Therefore, the 
total storage capacity of memory section may be reduced, thereby reducing 
the scale and cost of the device remarkably.