Recording method and device which provides an optimum setting of a record-carrier-dependent recording parameter

A recording method and corresponding recording apparatus adjusts at least one record carrier-dependent recording parameter (I.sub.s) which influences the quality of the recorded information pattern (58, 59). In determining an optimum setting of the parameter (I.sub.s) a calibration area (21) is selected from a predetermined number of such areas on the record carrier. The selected area is then provided with test patterns recorded at different settings of the recording parameter, and based on the test patterns thus formed an optimum setting of such parameter is determined in accordance with a predetermined criterion. The parameter is adjusted in accordance with such optimum setting thereof during the recording of the information pattern (58, 59). Each time such a calibration is performed an auxiliary pattern is recorded in an auxiliary area (22) assigned to the calibration area employed, which auxiliary pattern indicates that test patterns are present in such calibration area. For making a subsequent calibration, the calibration area to be used is selected on the basis on which of the auxiliary area (22a, . . . , 22d) already include auxiliary patterns.

BACKGROUND OF THE INVENTION 
1. Related Application 
This application is related to Applicant's copending application Ser. No. 
07/491,399, filed mar. 8, 1990, and also to his application Ser. No. 
07/542,287, filed concurrently herewith, since issued as U.S. Pat. No. 
5,072,435, dated Dec. 10, 1991, and his application Ser. No. 453,547, 
filed Dec. 20, 1989, since issued as U.S. Pat. No. 5,105,413, date Apr. 
14, 1992. All are assigned to the present assignee, and pertain, inter 
alia, to adjustment of a recording parameter of an information recording 
device. 
2. Field of the Invention 
The present invention relates to a method of recording information patterns 
on a record carrier, in which method at least one record-carrier-dependent 
recording parameter which influences the quality of the recorded 
information pattern is adjusted to an optimum value of such parameter. 
The invention further relates to an information recording device comprising 
write means for writing an information pattern on a record carrier and 
means for adjusting a record carrier-dependent-recording parameter of the 
write means to an optimum value of such parameter. 
This type of method and such a device are generally known, inter alia from 
European Patent Document EP-A-O,288,114. The method and the device 
described therein employ record carriers which have been provided with 
adjustment data, specifically the write signal waveform and write 
intensity, during fabrication of the record carriers. After insertion of 
the record carrier into the information recording device, the adjustment 
data is read from the record carrier and the write means are adjusted in 
conformity with the adjustment data thus read. However, the drawback of 
the prior-art device is that the resulting adjustment of the write means 
is not always found to be optimum for the combination of the particular 
recording device and record carrier which are employed. As a result of 
this, the dimensions of the recorded information patterns may exhibit 
deviations, so that the recorded information cannot always be read 
reliably. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a device of the 
described type, in which the adjustment of a write parameter of the write 
means is improved. With respect to the method, this object is achieved by 
selecting a calibration area from a number of possible predetermined 
calibration areas on the record carrier, forming test patterns in the 
selected calibration area for different settings of the parameter, 
determining the optimum setting of such parameter in accordance with a 
predetermined criterion on the basis of the test patterns thus formed, and 
adjusting the parameter in conformity with said optimum setting during the 
formation of the information patterns on the second carrier. 
Apparatus according to the invention comprises selection means for 
selecting a calibration area from a number of predetermined calibration 
areas on the record carrier, means for causing test patterns to be formed 
in the selected calibration area for different settings of a write 
parameter of the write means, means for selecting an optimum setting of 
such parameter on the basis of the test patterns thus formed, and means 
for adjusting the write parameter in conformity with the selected optimum 
setting during the formation of information patterns on the record 
carrier. 
The invention is based inter alia on Applicant's recognition of the fact 
that the optimum setting of the write parameter of the write means 
strongly depends not only on the record carrier used but also on the 
information recording device used. For a specific combination of a record 
carrier and a recording device, however, the optimum setting is found to 
remain substantially constant for the entire recording area of the record 
carrier. 
Therefore, the determination of the write adjustment data in a device in 
accordance with the invention may be considered to be optimum for the 
entire recording area of the record carrier. The use of a number of 
different calibration areas moreover enables the optimum setting to be 
determined several times, for example each time that the record carrier is 
loaded into a recording device. This is an advantage particularly when the 
same record carrier of a type which cannot be overwritten is used in a 
number of different information recording devices. The use of a plurality 
of calibration areas then also enables the optimum setting to be 
determined for each information recording device. In principle, the 
calibration area to be used can be selected by detecting which of the 
calibration areas have already been provided with test patterns. A 
drawback of this is that many of the test patterns are formed while the 
setting is not optimum, so that a reliable detection of the presence of 
the test patterns cannot be guaranteed. Moreover, the search for an unused 
calibration area may require considerable time owing to the total length 
of the calibration areas. 
If a table of contents is available which specifies how many information 
signals have already been recorded on the record carrier, the maximum 
number of calibration areas used can be derived from the contents of this 
table, assuming that the optimum setting was determined only once for 
recording each information signal. An unambiguous selection of a 
calibration area is then always possible on the basis of this number. The 
last-mentioned selection method has the drawback that once an optimum 
setting has been determined, it is not permissible to delay in recording 
the next information signal. This means that the process of determining 
the optimum setting must be postponed until it is absolutely certain that 
a signal is about to be recorded. This may lead to additional delays in 
the recording of further information signals. 
The drawbacks of the above selection methods are avoided by assigning an 
auxiliary area to each calibration area, an auxiliary pattern being 
formed, each time that an optimum setting is determined, in the auxiliary 
area assigned to the calibration area used for determining the optimum 
setting, a new calibration area being selected on the basis of the 
auxiliary patterns recorded in the auxiliary areas. 
The use of an auxiliary area makes it always possible to determine 
unambiguously which calibration areas have already been used. As the 
dimensions of the auxiliary areas can be substantially smaller than the 
dimensions of the calibration areas, selection of an unused calibration 
area can be made far more rapidly on the basis of the auxiliary areas than 
on the basis of the calibration areas themselves. 
If a record carrier is used which has already been provided with address 
information for the purpose of locating the calibration areas, it is 
advantageous if the calibration area used directly follows an area not 
already provided with test patterns. This is because when the test 
patterns are formed the address information may be damaged to such an 
extent that a correct reading of the address information is no longer 
guaranteed, and locating an area which is situated a short distance after 
an area with damaged address information may then give rise to problems. 
When record carriers are used whose calibration areas form part of a 
preformed servo track, applying the test patterns may cause the track to 
be damaged to such an extent that a correct tracking cannot be guaranteed. 
Preferably, the number of calibration areas is selected to be larger than 
or equal to the maximum number of information signals which can be 
recorded on a record carrier. (This number is one hundred for recording CD 
signals.) This guarantees that a calibration area for determining the 
adjustment is available for each information signal to be recorded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows an illustrative embodiment of an information recording device 
in accordance with the invention by means of which information can be 
recorded on a record carrier 1, for example an optical record carrier, 
which is rotated about an axis 2. The information recording device 
comprises a conventional read/write head 3, arranged opposite the rotating 
record carrier. By means of a customary positioning system, for example, 
in the form of a motor 4 and a spindle 5a, the read-write head 3 can be 
moved in a radial direction relative to the record carrier 1 under control 
of a customary control unit 5, which may take the form of a 
microprocessor. 
An information signal Vi to be recorded can be applied to a signal 
processing circuit 7 via an input 6. The signal processing circuit 7 is of 
a conventional type, which converts the applied input signal into a 
recording signal Vop of a suitable recording format, for example CD format 
or RDAT-format. The recording signal Vop is applied to a driver circuit 8 
of a customary type, which converts the recording signal Vop into a write 
signal Vs for the read/write head 3 in such a way that an information 
pattern corresponding to the recording signal Vop is recorded on the 
record carrier. For the purpose of reading the recorded information 
patterns, the read/write head 3 has an output for supplying a read signal 
V1 which is representative of the information pattern being read. The read 
signal V1 is applied to a read circuit 9 for recovering the information 
represented by the read signal V1. The driver circuit 8 is of an 
adjustable type, enabling one or more of the parameters which influence 
the quality of the recorded information pattern to be adjusted. When an 
optical read/write head is used, by which an information pattern of 
optically detectable effects is formed by means of a radiation beam, the 
intensity of the radiation beam is an important adjustment parameter which 
largely determines the quality of the recorded information pattern. If the 
read/write head is a magnetic or magneto-optical write head which 
generates a magnetic field for the purpose of forming an information 
pattern in the form of a magnetic effects (domains), the field strength of 
the generated magnetic field may be an important adjustment parameter. If 
the information pattern is formed by means of write pulses, the pulse 
width may be an important adjustment parameter. It is to be noted that the 
above-mentioned adjustment parameters are only few examples of the large 
number of adjustment parameters which are possible. In this respect 
reference may be made in particular to Dutch Patent Document NL-A-9000150, 
in which the adjustment parameter is a reference value for the speed with 
which the recording effects are formed on the record carrier. During the 
formation of such effects the intensity of the write beam is controlled to 
maintain the speed with which the effects are formed at the adjusted 
reference value. 
For determining the optimum setting of the write signal driver circuit 8 
the device comprises an analysis circuit 10, which derives from the read 
signal an analysis signal Va which is indicative of the quality of the 
information pattern being read. The optimum setting of the write parameter 
can be determined in a calibration procedure by forming test information 
patterns on record carriers for different settings of the write signal 
driver circuit 8, and by selecting, on the basis of the analysis signal Va 
obtained from the recorded patterns, the setting of the write signal 
driver circuit 18 for which the analysis signal indicates a recorded 
pattern of optimum quality. In principle, the information signal Vi may 
itself be employed for writing the test information patterns. However, it 
is also possible to employ a test signal generator 11 for this purpose, 
which may then be included, for example, in the signal processing circuit 
7. The optimum setting is determined under control of the control unit 5, 
which for this purpose is coupled to the analysis circuit 10, to the 
driver circuit 8, and to the test signal generator 11, if present. The 
control unit 5 is loaded with a suitable program or may comprise a 
suitable hardwired control circuit 15. Preferably, the optimum setting is 
determined in a calibration procedure which is carried out when a record 
carrier has been inserted in the information recording device. 
For determining the optimum setting, the record carrier has been provided 
with a number of calibration areas situated at predetermined locations 
thereon, for example at the beginning of a servo track intended for 
recording information patterns. FIG. 2 by way of illustration 
diagrammatically shows a servo track 20 in the form of a straight line. 
The servo track 20 comprises an area Pa intended for recording information 
signals. An area TA preceding the area PA is intended for applying test 
patterns for the purpose of determining the optimum adjustment. The area 
TA is divided into calibration areas 21a, . . . , 21d, each having a 
length adequate for a sufficient number of test patterns to perform the 
calibration procedure. At the beginning of each calibration procedure an 
unused calibration area 21 is selected and subsequently a test pattern is 
recorded in the selected calibration area 21 for each of several different 
settings of the adjustment parameter. These test patterns are read, and 
the optimum adjustment is selected on the basis of the analysis signal Va 
then generated. The selection of an unused calibration area at the 
beginning of the calibration procedure can be effected in a number of 
different ways. For example, it is possible to read the calibration areas 
and to detect whether a test pattern is present in the calibration area 
being read. On account of the length of the calibration areas this may 
take considerable time. Moreover, reading the test patterns may be 
problematic because in forming the test patterns the servo track may be 
damaged to such extent that local tracking is no longer possible. When the 
number of information signals already recorded is indicated in a part of 
the servo track, the maximum number of calibration areas already used can 
be determined on the basis thereof, if it is assumed that for recording 
each information signal only one calibration area is required in order to 
determine the optimum setting. If for the calibration procedure that 
calibration area is selected whose sequence number corresponds to the 
number of recorded information signals incremented by one, it will always 
be simple to find an unused calibration area. However, care must then be 
taken that an information signal is actually recorded each time after the 
optimum setting has been determined. This is in order to guarantee that 
the calibration area corresponding to one more than the number of recorded 
information signals specified in the table of contents is actually unused. 
The drawbacks of the above selection method can be mitigated by indicating 
in a separate area on the record carrier which calibration areas are still 
unused. This is possible, for example, in that after each calibration 
procedure a signal is recorded which indicates how many calibration areas 
have already been used. It is also possible to assign an auxiliary area to 
each calibration area and to form an auxiliary pattern in the associated 
auxiliary area after the use of the calibration area. In an area CA in 
FIG. 2 the auxiliary areas assigned to the calibration areas bear the 
reference numerals 22a, . . . , 22d. In this case an unused calibration 
area can be selected by detecting whether an auxiliary pattern is present 
in the auxiliary areas. The locations of the calibration areas 21 and the 
auxiliary areas 22 in the servo track 20 can be specified by addresses, 
which are recorded for example in the servo track. However, the locations 
of these areas may also be specified in another manner, for example by 
arranging these areas at predetermined distances from the center of 
rotation of a disc-shaped record carrier. 
For the selection of a calibration area the control unit is loaded with a 
suitable program. FIG. 3 by way of example gives a flow chart of such a 
program. The program is fetched at the instant at which the optimum 
setting is to be determined again, for example each time that a record 
carrier is loaded into an information recording device. The program 
comprises a step B1 in which the beginning of the area CA is located under 
control of the control unit 5. Once the area CA is reached, reading of the 
area CA is started in step B2 and it is checked whether auxiliary patterns 
are present in the auxiliary areas being read within the area CA. Once an 
auxiliary area is detected in which no auxiliary pattern has been recorded 
the address of the beginning of the associated calibration area is 
derived, in step B3, on the basis of the address of the detected auxiliary 
area, for example by means of a Table specifying the relationship between 
the start addresses of the calibration areas and the addresses of the 
auxiliary areas assigned thereto. Subsequently, in step B4 the calibration 
area having the address thus determined is located under control of the 
control unit 5 and in step B5 the calibration procedure is carried out. 
After step B5, an auxiliary pattern is formed in the auxiliary area 
assigned to the relevant calibration area in step B6. For recording the 
auxiliary patterns, the test signal or the information signal Vi applied 
to the recording device may be used. 
It is to be noted that when the test pattern is formed in the calibration 
area, the servo track may be mutilated to such an extent that the address 
information following the test patterns can no longer be read in a 
reliable manner. Therefore, it is preferred to select the calibration 
areas 21 in such way that always a calibration area is used which is 
preceded by an area not yet provided with test patterns. This can be 
achieved simply, for example, by using the last calibration area 21d for 
the first calibration procedure and by subsequently using each time the 
calibration area 21 which directly precedes the calibration area 21 last 
used. 
FIG. 4 depicts an illustrative embodiment of an information recording 
device in more detail. The device shown is of a type by means of which a 
standard CD signal can be recorded optically on an optical record carrier 
116. The optical record carrier 116 may be of a type provided with a 
radiation-sensitive layer of, for example, a phase-change material or a 
dye, which layer has been provided with a servo track intended for 
recording the information patterns. 
A record carrier of the above type is described comprehensively inter alia 
in Dutch Patent Documents NL-A-8800151 now U.S. Pat. No. 4,901,300, 
NL-A-8900766 and NL-A-8901145, the latter two respectively correspond to 
U.S. application Ser. Nos. 403,269 (filed Sep. 5, 1989) and 453,545 (filed 
Dec. 20, 1989). The record carrier described in these Patent Applications 
has a track modulation in the form of a track-wobble, the frequency being 
modulated in conformity with an address signal representing addresses in 
the form of absolute time codes ATIP. An optical read/write head 105 of a 
customary type is arranged opposite the rotating record carrier 116 and 
can be moved in a radial direction relative to the record carrier 116 by 
means of a positioning device, for example in the form of a motor 103 and 
a spindle 104. If desired, the read/write head 105 can be employed both 
for recording information patterns and for reading information patterns. 
For this purpose the read/write head 105 comprises a semiconductor laser 
for generating a radiation beam 107a whose intensity is variable by means 
of a driver circuit 107, which is described in detail in, for example, 
Dutch Patent Document NL-A-8901591 which corresponds to the 
above-identified related copending U.S. application Ser. No. 07/491 399. 
In known manner the radiation beam 107a is aimed at the servo track of the 
record carrier 116. The beam 107a is partly reflected from the record 
carrier 116, the reflected beam being modulated in conformity with the 
track wobble and, if an information pattern is present, also in conformity 
with the information pattern. The reflected beam is directed towards a 
radiation-sensitive detector 108a, which generates a read signal VI 
corresponding to the beam modulation. The signal VI comprises a component 
produced by the track wobble and having a frequency of approximately 22 
kHz at the nominal scanning velocity. By means of a motor control circuit 
108 for controlling the motor 100 the motor speed is controlled so as to 
maintain the frequency of the component produced in the read signal VI by 
the track wobble at substantially 22 kHz. The read signal VI is also 
applied to a detection circuit 109, which derives the time codes ATIP from 
the component produced in the read signal VI by the track wobble and 
applies these codes to a control unit comprising, for example, a 
microcomputer 110. Moreover, the read signal VI is applied to an amplifier 
circuit 111 having a high-pass characteristic to reject the signal 
components produced in the read signal VI by the track wobble. The read 
signal VI, from which the low-frequency components have thus been removed, 
is applied to the analysis circuit 85, which indicates the quality of the 
information pattern being read. An example of the analysis circuit will be 
described in hereinafter. The analysis signal Va on the output of the 
analysis circuit 65 is also applied to the microcomputer 110. The 
recording device further comprises a customary CIRC encoding circuit 112, 
to which the signal Vi to be recorded can be applied via a switch 115 
which is controlled by the microcomputer 110. The CIRC encoding circuit 
112 is arranged in series with a conventional EFM modulator 113. The EFM 
modulator has its output connected to the driver circuit 107. The driver 
circuit 107 is of a customary controllable type by means of which 
parameters which can influence the quality of the recorded information 
pattern can be adjusted. Such a parameter may be, for example, the 
intensity of the radiation beam during the formation of the information 
patterns. In the case that the information patterns are formed 
subsequently with radiation pulses of constant duration, this duration may 
be an important parameter for influencing the quality of the applied 
information pattern. In the case of magneto-optical recording, the 
strength of the magnetic field generated in the record-carrier area 
scanned by the radiation beam may be an important parameter. For the 
purpose of generating a test pattern, the recording device 1 may comprise 
a test signal generator 114, which generates for example a random digital 
signal or which generates a signal corresponding to the digital signal 
value zero (digital silence). However, it is to be noted that in 
principle, the information signal can also be used for the formation of 
test patterns. The signal generated by the signal generator 114 is applied 
to the CIRC encoding circuit 112 via the switch 115. The switch 115 is of 
a customary type which, depending on the control signal received from the 
control unit 110, transfers either the signal Vi to be recorded or the 
output signal of the signal generator 114. 
As stated above, the test patterns are preferably recorded at addressable 
locations on the record carrier 116. If the record carrier 116 is 
configured in conformity with the aforementioned Netherlands Patent 
Application NL-A-8900766, on which record carrier the servo track is 
divided, in this order, into an area (PMA) for recording a temporary table 
of contents (Temporary TOC), an area (Lead In Area) for the storage of the 
definitive table of contents (TODC), and a Program Area (PA), the area PCA 
with the calibration areas is preferably an area which precedes the area 
(PMA) for recording the temporary table of contents. By way of 
illustration FIG. 5 shows a layout of the servo track 117. Moreover, FIG. 
5 shows the addresses of the various areas indicated by means of absolute 
time codes ATIP expressed in minutes, second and frames. For example, the 
absolute time code ATIP for the beginning of the Program Area (PA) is 
0.00.00. The absolute time code ATIP at the beginning of the Lead-In Area 
is marked TsL. The absolute time code ATIP at the beginning of the area 
PMA is equal to TsL minus 0.13.25, while the beginning of the area TA has 
an absolute time code equal to TsL minus 0.35.65. Every absolute time code 
ATIP marks a servo-track portion having a length corresponding to one 
frame. For each calibration area 21, a number of 15 frames are available 
and for each auxiliary area 22 one frame is available. If the record 
carrier is used for recording standard CD signals the available length is 
amply sufficient to carry out one calibration cycle for every information 
signal to be recorded. This is because in accordance with the CD-standard 
the maximum number of different information signals (tacks) is one 
hundred. 
Since the read-out of the ATIP codes in the areas in which already a 
test-information pattern has been recorded is not always guaranteed, the 
sequence in which the calibration areas 21 are used is suitably from back 
to front, i.e. the first calibration area 21 to be used is situated at the 
end (i.e. near the boundary with the CA area) of the TA area. In this way 
it is achieved that an area used for determining the optical write 
intensity is always preceded by a comparatively large area in which no 
test pattern has been recorded yet. This is an advantage because in a 
servo-track portion in which the already a test pattern has been recorded 
the absolute time code ATIP cannot always be read reliably, although this 
is necessary for determining the beginning of the calibration area 21 to 
be used. The optimum write intensity can be determined as follows. Before 
a new information signal is recorded the address of the calibration area 
for recording a test-information pattern is derived on the basis of the 
auxiliary areas 22. In the example given in FIG. 5 five calibration areas 
(having the sequence numbers 1-5) have already been used, which is 
indicated by the hatched areas. This is represented by auxiliary patterns 
in the five auxiliary areas having the sequence numbers 1-5. These 
auxiliary areas are also hatched. The calibration area having the sequence 
number 6 can then be used for the next calibration cycle, which is 
indicated by five auxiliary areas 1-5 with auxiliary patterns. After 
selection of the calibration area, a test pattern is recorded with a 
number of different write-intensity settings in the selected calibration 
area. After this the recorded test pattern is read and by means of the 
analysis signal Va, it is determined in which part of the calibration area 
the test pattern is optimum. Subsequently, an information pattern is 
recorded in the associated auxiliary area (having the sequence number 6) 
with a write intensity corresponding to the write intensity with which the 
optimum test pattern has been recorded. 
The microcomputer 110 is loaded with a suitable control program for 
carrying out the calibration cycle. FIG. 6 is a flow chart of an example 
of such a program. In step S1 of this program the read/write head 105 is 
positioned opposite the CA auxiliary area on the record carrier under 
control of the microcomputer 110, addressing being effected by means of 
the absolute time codes ATIP in the read signal VI detected by the 
detection circuit 109. In step S2 the address of the calibration area 22 
to be used for recording the test pattern is determined on the basis of 
the information patterns recorded in the auxiliary areas 22. This can be 
effected simply by detecting whether the reflected beam 107 exhibits a 
high-frequency modulation during scanning of the auxiliary areas with the 
beam 107a. Such a high-frequency modulation can be detected by detecting 
the presence of a high-frequency signal component in the read signal V1. 
For this purpose the recording device may comprise a high-frequency 
detector 120 arranged between the read/write head 105 and the 
microcomputer 110. When a read circuit is employed for recovering recorded 
information from the read signal V1, the presence of a test pattern can be 
detected on the basis of the presence of an output signal of the read 
circuit. 
In step S3 the calibration area 21 having the aforesaid address is located 
under control of the microcomputer 110. Once this area is reached the 
write intensity Is is set to an initial value Io in Step S4. Preferably, 
the value of Io for the relevant record carrier is prerecorded on the 
record carrier in a manner as described in the aforementioned Dutch Patent 
Document NL-A-8901145, which corresponds to U.S. application Ser. No. 
453,545 filed on Dec. 20, 1989. This value can then be read prior to the 
calibration cycle. Moreover, under control of the microcomputer 110 the 
signal generator 114 is connected to the CIRC encoding circuit 112 by 
means of the controllable switch 114, so that an EFM modulated test signal 
determined by the output signal of the signal generator is generated by 
the EFM modulator 113. Finally, in step S5 the control signal L/S sets the 
driver circuit 107 in such a way that the write intensity Is of the beam 
107a is switched between the initial value Io and an intensity I1 in 
conformity with the EFM modulated signal Vefm on the output of the EFM 
modulator 113, which results in a test pattern corresponding to the EFM 
signal being recorded. In step S6 the absolute time code ATIP detected by 
the detection circuit 109 is read out by the computer 110. In step S7 it 
is ascertained whether this absolute time code has changed relative to the 
previous read-out. If this is not the case step S6 is repeated. If it has 
changed, it is determined in step S8 whether the absolute time code being 
read indicates the end of the calibration area. If this is not the case 
step S9 is carried out, in which the write intensity Is is incremented by 
a small step .sub..DELTA. I, after which the program proceeds with step 
S6. If in step S8 it is found that the end of the calibration area 21 has 
been reached, step S10 is performed in which the control L/S sets the 
driver circuit 107 in such a way that the intensity of the beam 1107 is 
maintained constant at the level I1. In step S11 the beginning of the said 
calibration area 21 is located and read again. In step S12 the analysis 
signal Va is read by the microcomputer 110. In step S13 it is checked 
whether the value of the analysis signal Va corresponds to the optimum 
quality of the test pattern. If this is not the case the program proceeds 
with step S12. In the other case the absolute time code detected by the 
detection circuit 109 is read out in step S14. Subsequently, in step S15 
the optimum write intensity corresponding to the absolute time code read 
in step S14 is computed. This is possible, for example, by determining the 
difference between the absolute time code last read and the time code 
corresponding to the beginning of the calibration area. By means of this 
difference it is possible to determine by how many steps .sub..DELTA. I 
the initial value Io has been incremented before the absolute time code 
ATIP last read was reached during recording of the test-information 
pattern. This number of steps and the initial value Io define the optimum 
write energy Iopt. Subsequently, in step S16 the write intensity Is is set 
to the optimum value Iopt. 
In step S17 the auxiliary area 22 is located which is associated with the 
calibration area used. In step S18, once this area has been reached, an 
auxiliary pattern is formed in this auxiliary area 22. 
During the formation of test patterns in the calibration procedure 
described above this is initially effected with a low write intensity, 
which is subsequently incremented in steps. This means that it is possible 
to guarantee that the address information at the beginning of the 
calibration area can always be read because the address information will 
not be mutilated by the test patterns formed at low write intensities. 
Suitable methods of determining the optimum write intensity will be 
described by way of example. An optically readable record carrier is 
provided with an information pattern comprising effects having varying 
reflection properties by scanning the record carrier with a radiation beam 
whose intensity I is switched between a low level Ii for which there are 
no changes in reflection and a high write level Is which produces a change 
in reflection in the scanned part of the record carrier. An example of 
such an intensity variation I and the associated pattern of effects 58 
having changed reflection properties and intermediate areas 59 having 
unchanged properties is given in FIG. 7. The information pattern of 
effects 58 and intermediate areas 59 can be read by scanning the pattern 
with a read beam of a constant intensity, which is low enough to preclude 
a detectable change in optical properties. During the scanning process the 
read beam reflected from the record carrier is modulated in conformity 
with the information pattern being scanned. The modulation of the read 
beam can be detected in a customary manner by means of a 
radiation-sensitive detector, which generates a read signal V1 which is 
indicative of the beam modulation. The read signal V1 is also shown in 
FIG. 7. The read signal V1 is reconverted into a bivalent signal by 
comparison of the read signal with a reference level Vref. For a reliable 
conversion it is desirable that the points where the read signal V1 
intersects the reference level are well-defined, in other words, the 
"jitter" in the read signal V1 should be minimal. As is known, jitter of 
the read signal V1 in optical recording is minimal if the information 
pattern is symmetrical, i.e. if the average length of the effects 58 is 
equal to the average length of the intermediate areas 59. The problem 
which then arises is that the length of the effects 58 strongly depends on 
the write intensity Is. If the write intensity is too high the effects 58 
will be too long and if the write intensity is too low the effects 58 will 
be too short. Therefore, an accurate adjustment of the write intensity is 
required. 
In a possible method of determining the optimum write intensity, test 
patterns can be recorded with the aid of a pulse-shaped signal having a 
50% duty cycle at different write intensities, after which the recorded 
test pattern can be read. The optimum setting can then be selected by 
determining for which setting the second harmonic distortion of the read 
signal V1 is minimal. 
Another method of determining the optimum write intensity, which is also 
described in the above-cited copending application Ser. No. 07/491,399, 
will be described in more detail with reference to FIG. 8. FIGS. 8a, 8b 
and 8c show the intensity variation I, the corresponding information 
pattern of effects 58 and intermediate areas 59, and the read signal V1 in 
the case that the write intensity Is is too low, optimum and too high 
respectively. 
In FIG. 8 the read signals V1 vary between a maximum level A1 and a minimum 
level A2. The level DC represents the value of the d.c. level in the read 
signal V1. As will be apparent from FIG. 6, the d.c. level DC of the read 
signal V1 is substantially centered between the levels A1 and A2 when the 
write intensity has the optimum value. If the write intensity is too low 
the d.c. level DC will be situated above the middle between the levels A1 
and A2, while in the case that the write level is too high the d.c. level 
DC will be situated below the middle between the levels A1 and A2. Thus, 
an optimum write intensity setting can be obtained by adjusting the write 
intensity Is to a value for which the d.c. level DC is situated 
substantially in the middle between the levels A1 and A2. 
An improvement of the above method of determining the optimum intensity, 
which is also disclosed in the aforementioned copending application, will 
be described with reference to FIG. 9a. In accordance with this method an 
information pattern is recorded for the purpose of determining the optimum 
intensity, which pattern comprises a plurality of sub-patterns 70 each 
comprising a short effect 58 and a short intermediate are 59, recorded by 
means of a write signal having a 50% duty cycle. The information pattern 
further comprises a second sub-pattern 71 comprising a comparatively long 
effect 58 and a comparatively long intermediate area 59, also recorded 
with the aid of a write signal having a 50% duty cycle. The number of 
sub-patterns 70 is selected to be substantially larger than the number of 
sub-patterns 71. FIG. 9a further shows the read signal V1 obtained in the 
case of reading with the aid of an optical read device. 
The dimensions of the sub-patterns 70 are selected in such a way that the 
amplitude of the signal components in the read signal V1 corresponding to 
these sub-patterns 70 is substantially smaller than the amplitude of the 
signal components corresponding to the sub-patterns 71. This can be 
achieved by selecting the dimensions of the sub-patterns 70 in such a way 
that only the 1st harmonic of this pattern is situated below the optical 
cut-off frequency of the optical scanning device. The dimensions of the 
sub-pattern 71 are selected in such a way that at least the 1st and the 
2nd harmonic of this pattern are situated below this optical cut off 
frequency. The d.c. level DC in the read signal V1 is dictated mainly by 
the signal components corresponding to the sub-patterns 70. The difference 
between the maximum value A1 and the minimum value A2 of the read signal 
V1 is dictated exclusively by the value corresponding to the sub-pattern 
71. As a change in write power Is has a substantially greater influence on 
the ratio between the lengths of the effects 58 and the intermediate areas 
59 of the sub-patterns 70 than on the ratio between these lengths for the 
sub-patterns 71, the d.c. level DC in the case of the method illustrated 
in FIG. 9a will also be far more susceptible to write level variations 
than in the case of the method illustrated in FIG. 8, where the amplitude 
of the read signal V1 is the same for all the sub-patterns occurring in 
the information pattern. All this means that the optimum write power can 
be determined far more accurately by means of the method illustrated in 
FIG. 9a. 
In addition to the information pattern shown in FIG. 9a, which has been 
recorded with an optimum write intensity, similar information patterns are 
shown in FIGS. 9b and 9c, which have been recorded at a write level which 
is too low and which is too high respectively. As will be apparent 
therefrom, the DC level in the case of the optimum write intensity is 
again substantially centered between the maximum signal value (A1) and the 
minimum signal value (A2) in the signal V1, while in the case of a write 
level which is too low or too high the DC level is situated above and 
below the center respectively. The illustrated information pattern is only 
one of the possible information patterns comprising a comparatively large 
number of sub-patterns comprising short effects and intermediate areas and 
a comparatively small number of sub-patterns comprising long effects and 
intermediate areas. A sub-pattern which is also very suitable is a pattern 
corresponding to an EFM signal in conformity with the CD standard. Such a 
pattern comprises areas of a length corresponding to at least 3 bits (I3 
effect) and at the most 11 bits (I11 effect). Approximately one third of 
all the effects in such a EFM pattern are I3 effects, whereas only 4% of 
all the effects are I11 effects. The dimensions of the I3 effects are such 
that only the fundamental of these effects is situated below the optical 
cut-off frequency of the optical read system. Of the I11 effects at least 
the 1st, the 2nd and the 3rd harmonic are situated below the optical 
cut-off frequency. 
FIG. 10 shows an example of the analysis circuit in FIG. 4 by means of 
which an analysis signal Va can be derived from the read signal V1 to 
indicate the extent to which the d.c. level DC deviates from the level 
corresponding to the optimum write intensity. The analysis circuit in FIG. 
10 is as disclosed in the aforementioned copending U.S. application, and 
comprises a low-pass filter 80 for determining the DC level of the read 
signal V1. It further comprises a positive-peak detector 81 for 
determining the maximum value A1 of the read signal V1 and a negative-peak 
detector 82 for determining the minimum value A2 of the read signal V1. 
The output signals of the peak detectors 81 and 82 are applied to 
non-inverting inputs of an adder circuit 83, while the output signal of 
the low-pass filter 80, after amplification to twice its value, is applied 
to an inverting input of the adder circuit 83, so that the output signal 
of the adder circuit, which signal constitutes the analysis signal Va, 
complies with Va=A1+A2-2DC and consequently indicates the extent to which 
the d.c. level DC deviates from the mean value of the maximum signal value 
A1 and the minimum signal value A2. 
For other suitable examples of analysis circuits reference is made to Dutch 
Patent Document NL-A-8901591 which corresponds to the aforementioned 
copending U.S. application. If the second harmonic distortion in the read 
signal is employed as a measure of the quality of the applied pattern, the 
analysis circuit may comprise a customary 2nd harmonic detector. 
It is to be noted that the invention is not limited to optical recording 
devices but may also be employed in other recording devices, such as for 
example magnetic recording devices or devices in which information is 
recorded by means of an electron beam. Although the invention can also be 
used for record carriers of a type which can be overwritten, the invention 
is particularly suitable for use in conjunction with record carriers of 
the write-once type.