Apparatus and method for measuring characteristics of optical pickup and/or optical disc

A device for measuring characteristic values of an optical pickup and/or an optical disc capable of detecting tracking signals for measuring characteristic values even if optical disc rotation is not subjected to eccentricity. The device for measuring characteristic values of an optical pickup and/or an optical disc 1 samples outputs of photodetectors of an optical pickup 2 as signals A to F directly by a sample-and-hold circuit 8 and an analog-to-digital converter 10 to store the resulting digital data in a second memory 11. An arithmetic-logic unit 12d measures tracking error signals based on the digital data stored in the second memory 11. A signal generating circuit 25 then sends a sine wave signal to a tracking coil 2b for moving the laser light illuminated on the optical disc along the radius of the disc.

FIELD OF THE INVENTION 
This invention relates to an apparatus and a method for measuring 
characteristics of an optical pickup and/or an optical disc. 
DESCRIPTION OF THE RELATED ART 
There has so far been known a device for inspecting characteristics of an 
optical pickup used in an optical disc drive. The device for inspecting 
characteristics of an optical pickup is used for example in carrying out 
inspection for shipment or reception of an optical pickup in connection 
with whether or not the optical pickup satisfies the prescribed 
specifications. 
FIG. 1 shows a block diagram of a conventional device 100 for inspecting 
characteristics of an optical pickup. 
The conventional device 100 for inspecting characteristics of an optical 
pickup shown in FIG. 1 is designed to inspect an optical pickup. 
The conventional device 100 for inspecting characteristics of an optical 
pickup includes a test bench 102 on which the optical disc is set, a 
matrix circuit 103 supplied with an output of a photodetector of the 
optical pickup 101 for outputting a playback signal (RF signal) and a 
servo control circuit 104 for performing servo control for reproducing an 
optical disc based on an output of the matrix circuit 103. 
The conventional device 100 for inspecting characteristics of an optical 
pickup also includes n measurement circuits 105a to 105n for measuring 
various characteristic values of the optical pickup based on an output of 
the matrix circuit 103, a multiplexer 106 for switching between outputs of 
the measurement circuits 105a to 105n and a multiplexer 106 for switching 
between outputs of the measurement circuits 105a to 105n. The conventional 
device 100 for inspecting characteristics of an optical pickup further 
includes an analog-to-digital converter 107 for converting an output of 
one of the circuits 105a to 105n selected by the multiplexer 106 into 
digital data and a computer 108 for statistically processing output data 
of the analog-to-digital converter 107 for displaying the results. 
The optical pickup 101 is a subject of inspection by this device 100 for 
inspecting characteristics of an optical pickup. The optical pickup 101 is 
detachably mounted on this device 100 for inspecting characteristics of an 
optical pickup. The optical pickup 101 includes a laser diode, a beam 
splitter, an objective lens and a photodetector. This optical pickup 101 
condenses a laser light beam outgoing from a laser diode via beam splitter 
and an objective lens on the optical disc. The optical pickup also forms 
an image of the reflected light from the optical disc on the 
photodetector. The photodetector provided on the optical pickup 101 is a 
photoelectric converting device and converts the imaged reflected light 
into electrical signals. 
The optical pickup 101 usually includes plural photodetectors. For example, 
the optical pickup 101 includes a four-segment photodetectors and a pair 
of photodetectors arranged on both sides of the four-segment 
photodetectors for side spot detection. Outputs of these photodetectors 
are routed to the matrix circuit 103. 
The test bench 102, on which is set the optical disc, runs this optical 
disc in rotation for reproducing the disc. The optical disc set on the 
test bench 102 is used as reference for this device 100 for inspecting 
characteristics of the optical pickup. 
The matrix circuit 103 is fed with outputs of the photodetectors of the 
optical pickup 101 to generate playback (RF) signals, focusing error (FE) 
signals and tracking error (TE) signals from the photodetector outputs. 
If the photodetector provided on the optical pickup 101 is made up of 
four-segment photodetectors and both side photodetectors for detecting 
side spots, the matrix circuit 103 outputs the following signals: That is, 
the matrix circuit 103 finds the sum of the respective outputs of the 
four-segment detectors to output the result as RF signal. The matrix 
circuit 103 also outputs FE signal by the astigmatic method. Specifically, 
the matrix circuit 103 computes the sums of the two photodetectors lying 
across the four-segment detectors to find the difference between the sums 
to output the resulting difference as the FE signal. The matrix circuit 
103 also computes the difference between the side spot detecting 
photodetectors to output the resulting difference as TE signal. 
The matrix circuit 103 routes the RF, FE and TE signals, thus computed, to 
the servo control circuit 104 and the measurement circuits 105a to 105n. 
The servo control circuit 104 performs servo control during reproduction of 
the optical disc based on the RF, FE and TE signals. Specifically, the 
servo control circuit 104 performs focusing servo control, tracking servo 
control, thread servo control and tilt servo control. 
The measurement circuits 105a to 105n calculate characteristic values of 
the optical pickup 101. The measurement circuits 105a to 105n measure 
respective different characteristic values. Therefore, the number of the 
measurement circuits 105a to 105n corresponds to that of the 
characteristic values to be measured. 
The measurement circuits 105a to 105n perform filtering, peak detection or 
frequency/voltage conversion by analog processing in order to compute the 
characteristic values. The first measurement circuit 105a measures the 
signal level of an S-shaped curve at the time of capturing a focusing 
servo loop based on, for example, the FE signals. The second measurement 
circuit 105b measures the level of the TE signals based on the TE signals. 
The third measurement circuit 105c measures the level of the RF signal 
based on the RF signal. The fourth measurement circuit 105d measures 
jitter components of the RF signal based on the RF signal. 
The multiplexer 106 switches between outputs of the measurement circuits 
105a to 105n to route an output of the selected measurement circuit to the 
analog-to-digital converter 107. 
The analog-to-digital converter 107 converts outputs of the measurement 
circuits 105a to 105n supplied via multiplexer 106 into digital data which 
is routed to the computer 108. The rate of conversion of the 
analog-to-digital converter 107 is low because the outputs of the 
measurement circuits 105a to 105n are substantially at the dc level. For 
example, the rate of conversion of the analog-to-digital converter 107 is 
on the order of 1 kHz. 
The computer 108 performs statistic processing of digital data supplied 
from the analog-to-digital converter 107 to display the results. 
In the conventional device 100 for inspecting characteristics of an optical 
pickup, as described above, the characteristic values of the optical 
pickup 101 are measured by, for example, n measurement circuits 105a to 
105n, with the number n corresponding to the number of the characteristic 
values to be measured. The measured results are displayed for the user on 
the computer 108. 
The method for measuring the level of the TE signal by this conventional 
device 100 for inspecting characteristics of the optical pickup is 
explained in detail. 
This device 100 for inspecting characteristics of the optical pickup 
measures the level of the TE signal using eccentricity of rotation of the 
optical disc. 
Such eccentricity of rotation of the optical disc occurs when the center of 
the optical disc set on the test bench 102 for rotational driving is 
offset from the axis of rotation. 
For example, if eccentricity of rotation is caused in optical disc 
rotation, the optical disc is set on the test bench 102 so that the center 
O of the optical disc D differs from the axis of rotation of the optical 
disc D, as shown in FIG. 2. Therefore, the separation x between a position 
of irradiation Lx on the optical disc D of the laser light beam L radiated 
from the optical pickup and the center O of the optical disc D is varied 
with the rotational position of the optical disc D. 
Specifically, if the center O of the optical disc D is furthest from the 
point of illumination Lx of the laser light beam L, this distance x 
becomes a distance x1 corresponding to the distance between the axis of 
rotation and the point of illumination of the laser light beam Lx plus the 
distance between the axis of rotation and the center O of the optical disc 
D. If the optical disc D is rotated by 1/4 from the rotational position 
shown in FIG. 2A, the distance x becomes equal to the distance x2, as 
shown in FIG. 2A. If the optical disc D is rotated by 1/2 from the 
rotational position shown in FIG. 2B, the center O of the optical disc D 
becomes closest to the point of illumination of the laser light beam Lx, 
with the distance x becoming equal to a distance x3 corresponding to the 
distance between the axis of rotation and the center O of the optical disc 
D minus the distance between the axis of rotation and the center O of the 
optical disc D, as shown in FIG. 2C. If the optical disc D is rotated by 
1/2 from the rotational position shown in FIG. 2C, the distance x becomes 
equal to x4 as shown in FIG. 2D. 
Therefore, if the rotation of the optical disc D undergoes eccentricity, 
the point of illumination Lx on the optical disc D of the laser light beam 
L illuminated on the optical disc D is varied in synchronism with the 
rotational period of the optical disc D. Specifically, the point of 
illumination Lx on the optical disc D of the laser light beam L 
illuminated on the optical disc D is moved back and forth through the 
distances x3 to x1 from the center O of the optical disc D, as shown in 
FIG. 3. Thus, the point of illumination Lx traverses plural recording 
tracks due to eccentricity of rotation of the optical disc D. 
For measuring the TE signal level by the conventional device 100 for 
inspecting characteristics of an optical pickup, focusing servo control is 
performed on the optical disc subjected to eccentricity of rotation as 
described above. With this device 100 for inspecting characteristics of an 
optical pickup, the radial position of the optical pickup with respect to 
the optical disc is fixed, with the tracking servo circuit being turned 
off. With the device 100 for inspecting characteristics of an optical 
pickup, the optical disc is run in rotation, with the focusing servo on 
and with the tracking servo off, for detecting the TE signal produced with 
the rotational eccentricity using, for example, the measurement circuit 
105b. 
With the device 100 for inspecting characteristics of an optical pickup, 
the TE signal detected by the measurement circuit 105b is integrated for 
averaging the TE signal level for measuring the resulting averaged signal 
level. The value measured by the measurement circuit 105b is taken into 
the computer 108 for display for the user. 
With the device 100 for inspecting characteristics of an optical pickup, 
the TE signal level can be measured using rotational eccentricity of the 
optical disc, as described above. 
In the conventional characteristics inspection device for an optical 
pickup, in which TE signals are detected using rotational eccentricity of 
the optical disc, as described above, the TE signal detection becomes 
impossible if the optical disc is set correctly on the test bench 102 such 
that optical disc rotation is not subjected to rotational eccentricity. 
SUMMARY OF INVENTION 
According to the present invention, there is provided an apparatus for 
measuring characteristics of an optical pickup and/or an optical disc 
comprising: 
focusing servo control means for controlling a focal point position of a 
laser light beam illuminated on the optical disc, based on an output of a 
photoelectric converting unit of the optical pickup, for focusing the 
laser light beam on a recording surface of the optical disc; 
laser control means for controlling the optical pickup for reciprocating 
the laser light along the radius of the optical disc; and 
characteristics detection means for detecting a signal for generating 
tracking error signals from an output of the photoelectric converting 
device of the optical pickup, and for measuring the characteristic values 
of the optical pickup and/or the optical disc based on the signal. 
The laser control means may impart an optional wave form signal to a 
tracking coil adapted for moving the laser light along the radius of the 
optical disc for reciprocating the illuminated position of the laser light 
along the radius of the optical disc. 
The characteristics detection means may detect the control amount of the 
laser control means for detecting sensitivity of a tracking coil adapted 
for moving the laser light along the radius of the optical disc based on 
the control amount of the laser control means, track pitch as defined by 
the optical disc and on the tracking signals. 
The characteristics detection means may detect a signal for generating the 
tracking error signals from an output of the photoelectric converting 
device of the optical pickup, detect a vicinity of a transition point in 
the movement direction of the illuminated position of the reciprocated 
laser light, remove a signal portion of the signal generating the tracking 
error signals in the vicinity of the transition point and measure the 
characteristic values of the optical pickup and/or the optical disc based 
on the signal freed of the signal portion in the vicinity of the 
transition point. 
According to another aspect of the invention, there is provided a method 
for measuring characteristics of an optical pickup and/or an optical disc 
comprising: 
controlling the focal position of the laser light illuminated on the 
optical disc based on an output of the photoelectric converting device of 
the optical pickup for focusing the laser light on a recording surface of 
the optical disc; 
controlling the optical pickup for reciprocating the illuminated position 
of the laser light along the radius of the optical disc; 
detecting a signal for generating the tracking error signals from an output 
of the photoelectric converting device of the optical pickup; and 
measuring the characteristic values of the optical pickup and/or the 
optical disc based on the signal. 
An optional wave form signal may be imparted to a tracking coil moved 
radially of the optical disc for reciprocating the illuminated position of 
the laser light along the radius of the optical disc. 
The method for measuring characteristics of an optical pickup or an optical 
disc may further comprise: 
detecting the control amount of the laser control means for detecting the 
sensitivity of the tracking coil adapted for moving the laser light along 
the radius of the optical disc based on the control amount of the laser 
control means, track pitch defined by the optical disc and on the tracking 
signals. 
The method for measuring characteristics of an optical pickup or an optical 
disc may further comprise: 
detecting a signal for generating tracking error signals from an output of 
the photoelectric converting device of the optical pickup; 
detecting the vicinity of a transition point of the movement direction of 
the illuminated position of the reciprocated laser light; 
removing a signal portion of the signal for generating the tracking error 
signals lying in the vicinity of the transition point; and 
measuring the characteristic values of the optical pickup and/or the 
optical disc based on the above signal freed of the signal portion lying 
in the vicinity of the transition point.

DESCRIPTION OF THE EMBODIMENTS 
Referring to the drawings, a preferred embodiment of the present invention 
will be explained in detail. 
The device for inspecting characteristics of an optical pickup embodying 
the present invention, referred to hereinafter as a device for inspecting 
characteristics or a characteristics inspecting device, inspects 
characteristics of an optical pickup employed in an optical disc drive. 
This sort of the characteristics inspecting device is used for inspecting 
specifications or characteristics of the optical pickup in, for example, 
shipment or acceptance tests of the optical pickup. 
FIG. 4 shows a block diagram of a device for inspecting characteristics 1 
embodying the present invention. 
The device for inspecting characteristics 1 is used for inspecting 
characteristics of an optical pickup 2. 
The device for inspecting characteristics 1 includes a test bench 3 on 
which to set an optical disc, a matrix circuit 4 fed with an output of a 
photodetector of the optical pickup 2 for outputting a playback (RF) 
signal and a servo control circuit 5 for performing servo control for 
reproducing an optical disc based on an output of the matrix circuit 4. 
The device for inspecting characteristics 1 also includes a focusing servo 
circuit 22, a focusing amplifier 23 for amplifying an output of the 
focusing servo circuit 22 for supplying an output of the optical pickup 2 
to a focusing coil 2a of the optical pickup 2, a tracking servo circuit 
24, signal generating circuit 25, a switch 26 for switching between 
outputs of the tracking servo circuit 24 and the signal generating circuit 
25, and a tracking amplifier 27 for amplifying an output of the tracking 
servo circuit 24 or the signal generating circuit 25 supplied via switch 
26 for supplying an amplified output to the tracking coil 2b of the 
optical pickup 2. 
The device for inspecting characteristics 1 also includes a first 
analog-to-digital converter 6 for converting RF signals of the matrix 
circuit 4 to digital signals and a first memory 7 for transiently storing 
output data of the first analog-to-digital converter 6. 
The device for inspecting characteristics 1 further includes first to sixth 
sample-and-hold circuits 8a to 8f for sample-holding outputs of the 
photodetectors of the optical pickup 2, a multiplexer 9 for switching 
outputs of the first to sixth sample-and-hold circuits 8a to 8f, a second 
analog-to-digital converter 10 for converting the outputs of the first to 
sixth sample-and-hold circuits 8a to 8f into digital data and a second 
memory 11 for transiently storing output data of the second 
analog-to-digital converter 10. 
The device for inspecting characteristics 1 also includes a third 
analog-to-digital converter 28 for converting a signal of a pre-set 
control amount for tracking servo by the servo control circuit 5 into 
digital data and a third memory 29 for transiently storing output data of 
the third analog-to-digital converter 28. 
The device for inspecting characteristics 1 additionally includes a 
computer 12 for computing characteristic values of the optical pickup 2 
based on the digital data transiently stored in the first memory 7 and in 
the second memory 11 for displaying the computed results and for 
controlling the servo control circuit 5 based on the computed results. 
The optical pickup 2 is the subject of inspection by this device for 
inspecting characteristics 1. The optical pickup 2 is detachably mounted 
on this device for inspecting characteristics 1. The optical pickup 2 
includes a laser diode, a beam splitter, an objective lens and a 
photodetector. This optical pickup 2 condenses a laser light beam outgoing 
from a laser diode via beam splitter and an objective lens on the optical 
disc. The optical pickup also forms an image of the reflected light from 
the optical disc on the photodetector. The photodetector provided on the 
optical pickup 101 is a photoelectric converting device and converts the 
imaged reflected light into electrical signals. 
The optical pickup 2 includes plural photodetectors. FIG. 5 shows an 
example of plural photodetectors provided on the optical pickup 6. 
The optical pickup 2 includes four photodetectors A to D, arrayed in a 2 2 
matrix configuration, and photodetectors E and F arrayed on both sides of 
the photodetectors A to D for side spot detection, as shown for example in 
FIG. 5. These photodetectors A to F are used in, for example, a so-called 
three-spot optical pickup adapted for radiating three laser light beams to 
the optical disc. The photodetectors A to D are irradiated with a main 
beam as a center beam in the three-spot system. That is, the 
photodetectors A to D are irradiated with reflected light from recording 
pits recorded on the recording track of the optical disc. The 
photodetectors E and F are arranged on both sides of the photodetectors A 
to D in the radial direction of the optical disc. The photodetectors E and 
F are irradiated with side beams of the three-spot system. For example, 
the photodetectors E and F are irradiated with light reflected from, for 
example, the edges of the optical disc track. 
The photodetectors A to F convert the light volume of the illuminated 
reflected light into signals A to F. The optical pickup 2 routes these 
signals A to F to the matrix circuit 4. The optical pickup 2 sends the 
signals A to F to the first to sixth sample-and-hold circuits 8a to 8f, 
respectively. 
The test bench 3, on which is set the optical disc, runs the optical disc 
in rotation for reproducing the disc. The optical disc, set on this test 
bench 3, is used as a reference for this characteristics inspection device 
1. That is, the characteristics inspection device 1 measures 
characteristics of the optical pickup 2 based on the playback signals of 
the optical disc used as the reference. 
The matrix circuit 4 is fed with signals A to F outputted by the 
photodetectors A to F of the optical pickup 2 for generating playback (RF) 
signals, focusing error (FE) signals and tracking error (TE) signals based 
on these signals A to F. The matrix circuit 4 generates these RF, FE and 
TE signals based n the signals A to F as follows: That is, the matrix 
circuit 4 computes A+B+C+D based on the signals A to D to generate RF 
signals. On the other hand, the matrix circuit 4 outputs FE signals by the 
astigmatic method. Specifically, the matrix circuit 4 computes (A+C)-(B+D) 
based on the signals A to D to output the computed results as FE signals. 
On the other hand, the matrix circuit 4 computes E-F based on the signals 
E and F and sends the computed results as TE signals. 
The matrix circuit 4 sends the computed RF, FE and TE signals to the servo 
control circuit 5. Also, the matrix circuit 4 sends the RF signals to the 
first analog-to-digital converter 6. 
The servo control circuit 5 performs servo control for reproducing the 
optical disc based on the RF, FE and TE signals. 
The focusing servo circuit 22 is fed with the FE signals from the matrix 
circuit 4. The focusing servo circuit 22 applies pre-set filtering to the 
FE signals and then sends a signal of a control amount to reduce the FE 
signals to zero via focusing amplifier 23 to the focusing coil 2a of the 
optical pickup 2. This focusing servo circuit 22 thus controls the laser 
light radiated by the optical pickup 2 so that the focal point of the 
laser light radiated by the optical pickup 2 will lie correctly on the 
recording surface of the optical disc. 
The tracking servo circuit 24 is fed with TE signals from the matrix 
circuit 4. The tracking servo circuit 24 performs filtering on the TE 
signals and sends a signal of a control amount to reduce the TE signals to 
zero via tracking amplifier 27 to the tracking coil 2b of the optical 
pickup 2. This tracking servo circuit 24 thus controls the laser light 
radiated by the optical pickup 2 so that the laser light radiated by the 
optical pickup 2 will correctly illuminate the recording track of the 
optical disc. 
The signal generating circuit 25 outputs a pre-set control signal (an 
optional waveform signal such as a sine wave signal, sawtooth wave signal, 
etc.) which is routed via tacking amplifier 27 to the tracking coil 2b of 
the optical pickup 2. The signal generating circuit 25 sends a preset 
control signal to the tracking coil 2b for radially moving the laser light 
radiated by the optical pickup 2 on the optical disc. The signal 
generating circuit 25 also sends a repetitive signal, such as a sine wave 
signal, for reciprocating the illuminating position of the laser light on 
the optical disc by the optical pickup 2 for traversing a pre-set number 
of tracks. 
The switch 26 switches between outputs of the tracking servo circuit 24 and 
the signal generating circuit 25 for supplying the selected output via 
tracking amplifier 27 to the tracking coil 27b. The switching of the 
switch 26 is controlled by the computer 12. 
The servo control circuit 5 also detects dc components of the FE signals to 
perform thread servo control of the optical pickup 2 so that these dc 
components will be zero. The servo control circuit 5 also performs tilt 
servo control for controlling the tilt of the optical disc based on the RF 
signals. Meanwhile, this servo control circuit 5 may be provided with a 
separate disc tilt detection unit for tilt servo control. 
The first analog-to-digital converter 6 converts the RF signals supplied 
from the matrix circuit 4 into digital data at a high sampling frequency, 
such as at a sampling frequency of, for example, 30 MHz. The first 
analog-to-digital converter 6 sends the RF signals converted into digital 
data to the first memory 7. 
The first memory 7 transiently stores the RF signals converted into digital 
data by the first analog-to-digital converter 6. 
The sample-and-hold circuits 8a to 8f are fed from the optical pickup 2 
with the signals A to F as photodetector output signals. The 
sample-and-hold circuits 8a to 8f sample-hold the signals A to F 
simultaneously using the same clocks. The clocks supplied to these 
sample-and-hold circuits 8a to 8f are at frequencies not lower than, for 
example, 50 kHz. Thus, the sample-and-hold circuits 8a to 8f repeat the 
sampling and holding operations with the clock of not less than 50 kHz as 
one cycle. 
The multiplexer 9 switches between outputs of the sample-and-hold circuits 
8a to 8f for supplying one of the sample-held outputs to the second 
analog-to-digital converter 10. This multiplexer 9 operates at a rate not 
less than six times as high as 50 kHz, if the sample-and-hold circuits 8a 
to 8f perform sample-holding operations with the clocks of 50 kHz, so that 
the sample-held outputs of the sample-and-hold circuits 8a to 8f can be 
supplied within one clock to the second analog-to-digital converter 10. 
The second analog-to-digital converter 10 converts all sample-held outputs 
of the sample-and-hold circuits 8a to 8f supplied thereto via multiplexer 
9 into digital data which is supplied to the second memory 11. This second 
analog-to-digital converter 10 has a conversion rate sufficient to convert 
outputs of the sample-and-hold circuits 8a to 8f within one cycle of the 
clocks suppled to the sample-and-hold circuits 8a to 8f. Since there are 
six sample-and-hold circuits 8a to 8f, the second analog-to-digital 
converter 10 achieves the conversion at a conversion rate not less than 
300 kHz if the sample-and-hold circuits 8a to 8f repeat the sample-hold 
operations by 50 kHz clocks. 
The sample-and-hold circuits 8a to 8f, multiplexer 9 and the second 
analog-to-digital converter 10 convert the signals A to F outputted by the 
photodetectors of the optical pickup 2 independently into digital data. 
Moreover, the sample-and-hold circuits 8a to 8f, multiplexer 9 and the 
second analog-to-digital converter 10 convert the signals A to F into 
digital data at the sampling frequency of, for example, not less than 50 
kHz. 
In the characteristics inspection device 1, the signals A to F as 
photodetector output signals of the optical pickup 2 can be converted into 
digital data by means other than the above-described sample-and-hold 
circuits 8a to 8f, multiplexer 9 and the second analog-to-digital 
converter 10. For example, the characteristics inspection device 1 may be 
comprised of six parallel rows of the analog-to-digital converters each 
having the sampling frequency of 50 kHz. 
The second memory 11 transiently stores the signals A to F of the optical 
pickup 2 converted into digital data by the second analog-to-digital 
converter 10. 
The third analog-to-digital converter 28 converts the control signal 
supplied to the second tracking coil 2b of the optical pickup 2 into 
digital data at a pre-set sampling frequency. The third analog-to-digital 
converter 28 sends the control signal converted into digital data in the 
third memory 29. 
The third memory 29 transiently stores the tracking servo control signal 
converted into the digital data by the third analog-to-digital converter 
28. The data transiently stored in the third memory 29 is sent to the 
arithmetic-logic unit 12d of the computer 12. The computer 12 includes, 
for example, an interfacing section 12a, a data storage section 12b, an 
output section 12c and an arithmetic-logic unit 12d. The interfacing 
section 12a outputs a control signal controlling the servo control circuit 
5 to this servo control circuit 5. The data storage section 12b has stored 
therein processing programs corresponding to measurement items of the 
optical pickup 2 by the characteristics inspection device 1. The output 
section 12c displays measured results of the characteristics of the 
optical pickup 2. 
The arithmetic-logic unit 12d of the computer 12 reads out the RF signals 
converted into the digital data from the first memory 7 for detecting 
jitter components of the RF signals based on the read-out data. The 
arithmetic-logic unit 12d of the computer 12 also reads out the signals A 
to F, converted int digital data, from the second memory 11, and executes 
arithmetic-logic operations on the measurement items for measuring the 
characteristics of the optical pickup 2. In addition, the arithmetic-logic 
unit 12d of the computer 12 also reads out the tracking control signal 
converted into digital data stored in the third memory 29 for measuring 
the sensitivity of the tracking coil 2b. 
In carrying out the processing for the respective measurement items, the 
arithmetic-logic unit 12d of the computer 12 performs the following 
arithmetic-logic operations on the data stored in the first memory 7 and 
the second memory 11. For example, the arithmetic-logic unit 12d performs 
filtering, peak level calculations, calculations of the waveform period, 
calculations of the phase difference of two signals, signal extraction by 
a level window, signal extraction by a periodic window and calculations of 
the ac and dc signal components. 
The items of measurement by the characteristics inspection device 1 are 
hereinafter explained. 
The present characteristics inspection device 1 measures the following 
items for searching the characteristics of the optical pickup 2: 
RF signal level (P1) 
I.sub.TOP and I.sub.BOTTOM of the RF signal (P2) 
Jitter of RF signal (P3) 
Beam position of the main beam (P4) 
TE signal level (P5) 
E-F balance (P6) 
E-F phase difference (P7) 
S-letter level (P8) 
S-letter balance (P9) 
Defocusing (P10) 
Cross-talk (P11) 
Astigmatic Aberration (P12) 
The processing programs for these items of measurement are stored in the 
data storage section 12b as processing programs P1 to P12. Based on, for 
example, user setting, the arithmetic-logic unit 12d reads out from the 
data storage unit 12b the processing programs P1 to P12 associated with 
the measurement items for performing arithmetic-logic operations on the 
data stored in the first memory 7 or the second memory 11. In the 
processing programs P1 to P12, measurement of the above items is carried 
out using the filtering, peak level calculations, calculations of the 
waveform period, calculations of the phase difference of two signals, 
signal extraction by a level window, signal extraction by a periodic 
window and calculations of the ac and dc signal components as described 
above. 
The processing for measuring the above-mentioned TE signal level and the 
E-F phase difference is hereinafter explained. 
First, with the present characteristics inspection device 1, the focusing 
servo circuit 22 effects focusing servo control with the focusing servo 
loop turned on. 
The characteristics inspection device 1 then sets the switch 26 of the 
servo control circuit 5 to the side of the signal generating circuit 25 to 
send a signal of a pre-set control volume outputted by the signal 
generating circuit 25 to the tracking coil 2b of the optical pickup 2. 
With the present characteristics inspection device 1, if the signal of the 
pre-set control volume is a e.g. a sine wave signal, the illuminating 
position of the laser light is reciprocated through a pre-set range on the 
optical disc. 
The arithmetic-logic unit 12d reads out digital data corresponding to the 
signals E and F from the second memory 11. Then, data corresponding to the 
signals E and F and the TE signal corresponding to the signal E minus 
signal F are computed and displayed for the user by the output unit 12c. 
FIG. 6 shows an example of measured data displayed by the output unit 12c. 
Specifically, FIGS. 6A, 6B and 6C show the signal E, signal F and the 
signal TE corresponding to (E-F). 
The arithmetic-logic unit 12d detects peak values of the signal E, signal F 
and the signal TE read out from the second memory 11. The arithmetic-logic 
unit 12d then measures the interval between the peak values to find the 
periods of the respective waveforms. The arithmetic-logic unit 12d then 
compares the periods thus found with pre-set thresholds to detect signals 
having the waveforms exceeding preset periods. The arithmetic-logic unit 
12d then finds data of the signals E, F and TE freed of data of signal 
portions the periods of which exceed pre-set threshold values. 
The arithmetic-logic unit 12d thus removes the portions of the signals E, F 
and TE the periods of which exceed the pre-set thresholds to derive 
signals freed of unstable signal portions caused by reciprocation of the 
illuminated portions on the optical disc of the laser light beam caused by 
eccentricity. Specifically, the waveform signals the periods of which 
exceed pre-set periods are those signals in the vicinity of the turning 
points of the reciprocating movements of the illuminated positions of the 
laser light beam caused by eccentricity of rotation represented by signals 
from time t11 until time t12 in FIG. 6. 
Based on the data freed of the signal portions the periods of which exceed 
pre-set periods, the arithmetic-logic unit 12d finds the E-F phase 
difference between the signals E and F while detecting an average value of 
the TE signal to find the TE signal level. 
Thus, with the characteristics inspection device 1, the tracking error 
signals can be obtained by controlling the illuminated position of the 
laser light radiated by the optical pickup 2 even although the optical 
disc rotation is not subjected to eccentricity, thus enabling the E-F 
phase difference and the TE signal level. 
Also, with the characteristics inspection device 1, the signal level of the 
control signal supplied to the tracking coil 2b when the arithmetic-logic 
unit 12d measures the E-F phase difference and the TE signal level can be 
detected by the third analog-to-digital converter 28 and the third memory 
29 for measuring the tracking actuator sensitivity. 
Specifically, if the track pitch of the optical disc is P (equal to 1.6 m 
if the disc is a compact disc), the number of tracks traversed during a 
period and the voltage supplied to the tracking coil 2b is V.sub.P-P, the 
sensitivity can be found by the following equation: 
EQU (Sensitivity of the tracking actuator)=(N P)/V.sub.P-P 
Although the foregoing description has been made on the characteristics 
inspection device 1 adapted for measuring the characteristics of the 
optical pickup 2, this device 1 can also be adapted for inspecting the 
characteristics of an optical disc. That is, while an optical disc set on 
the test bench 3 is used as a reference, it is also possible to measure 
characteristics of an optical disc by employing an optical pickup as a 
reference. 
Although the optical pickup 2 measured by the characteristics inspection 
device 1 measures the signals A to F using the photodetectors shown in 
FIG. 5, the present invention is not limited to the use of such optical 
pickup. For example, the present invention is applicable to an optical 
pickup for a magneto-optical disc or an optical pickup for a phase 
transition disc. In these cases, the photodetector differs in structure 
from the photodetectors explained with reference to FIG. 2, so that the 
numbers of the sample-and-hold circuits 8a to 8f or the second 
analog-to-digital converters 10 correspond to the number of the 
photodetectors. On the other hand, if the disc is a magneto-optical disc, 
the playback signal is a difference signal exploiting the Kerr effect. 
Therefore, the processing contents of the program in the arithmetic-logic 
unit 12d is matched to this difference signal. 
In summary, with embodiments of the present device for measuring 
characteristic values of the optical pickup and/or the optical disc, the 
optical pickup is controlled for moving the illuminated position of the 
laser light along the radius of the optical disc for measuring the 
characteristic values of the optical pickup and/or the optical disc based 
on the signal adapted for generating tracking error signals. 
In summary, the optical pickup is controlled for moving the illuminated 
position of the laser light along the radius of the optical disc for 
measuring the characteristic values of the optical pickup and/or the 
optical disc based on the signal adapted for generating tracking error 
signals. 
With embodiments of the method and the device for measuring characteristic 
values of the optical pickup and/or the optical disc, tracking signals can 
be measured for measuring the characteristic values even if the optical 
disc rotation s not subjected to eccentricity. Moreover, the tracking coil 
sensitivity can be detected easily. 
The embodiments have been advanced by way of example only and modifications 
are possible within the spirit and scope of the invention as defined in 
the appended claims.