Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Converting input voltage to output current or vice versa
Reexamination Certificate
2001-07-03
2002-11-12
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Converting input voltage to output current or vice versa
Reexamination Certificate
active
06480042
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a current-to-voltage converting circuit, an optical pickup head apparatus, an apparatus and a method for recording, reproducing or erasing data on an optical disk.
2. Description of the Related Art
Optical memory technologies for recording a large volume of information data on optical disks, each disk having a pattern of pits and used as a high-density, mass-storage recording medium, have now been marketed worldwide in the form of digital audio disks, video disks, text file disks, and data file disks. In particular, digital versatile discs (DVDs) which are recently popularized are optical high-density recordable disks which use a visible light with 650 nm wavelength from a semiconductor laser of a light source. A variety of recording media such as DVD-ROM for read-only operation, DVD-R capable of recording only one time, and DVD-RAM capable of recording a plurality of times are standardized.
FIG. 12
is a schematic view of an optical system of a conventional optical pickup head apparatus for reading data from a DVD-ROM disk as a recording medium. A semiconductor laser
1
emits divergent beam
70
which is linearly polarized and has a wavelength &lgr;1=650 nm. The beam
70
is reflected on a half-mirror
7
and changed with a path of the beam
70
. Subsequently, the beam
70
passes through a collimate lens
8
having 20 mm of a focusing distance, and is collimated to a parallel beam. The beam
70
is then converged by an object lens
9
having 3 mm of a focusing distance, is passed through a transparent substrate
40
a
of a recording medium
40
, and focused on a data recording surface
40
b.
The aperture of the object lens
9
is limited by an aperture
12
, where a numeral aperture (NA) is set to 0.6. The thickness of the transparent substrate
40
a
is 0.6 mm. The beam
70
reflected on the data recording surface
40
b
passes through the object lens
9
, and the collimate lens
8
. Then the beam
70
passes through the half-mirror
7
to be added with an astigmatism, passes through a concave lens
11
of which optical axis is inclined to correct a comma added at the passage through the half-mirror
7
, and received by a photo detector
31
. An axis
31
e
is an axis parallel with an image of a track provided on the data recording surface
40
b
of the recording medium
40
in the beam
70
received on the photo detector
31
.
The photodetector
31
has four photo receivers
31
a
to
31
d
for outputting current signals I
31
a
to I
31
d
according to amount of received light, respectively. Size of each of photo receivers
31
a
to
31
d
is 50 &mgr;m×50 &mgr;m. The current signals I
31
a
to I
31
d
are fed into corresponding circuits
50
a
to
50
d
of a current-to-voltage converting circuit
50
to be converted into voltage signals V
50
a
to V
50
d,
respectively. The voltage signals V
50
a
to V
50
d
are then released from the optical pickup head apparatus.
A focusing error signal is calculated from the output signals V
50
a
to V
50
d
of the optical pickup head apparatus by an astigmatic method, that is, by a calculation of (V
50
a
+V
50
c
)−(V
50
b
+V
50
d
). A tracking error signal is calculated by a phase difference method of comparing the phases of the signals V
50
a
to V
50
d
when the recording medium is a DVD-ROM or by a push-pull method when the recording medium is a DVD-RAM, that is, by a calculation of (V
50
a
+V
50
d
)−(V
50
b
+V
50
c
). The focusing error signal and the tracking error signal are then amplified to a desired level, and phase-compensated. Subsequently the signals are transferred to actuators
91
and
92
for focusing and tracking control.
FIG. 13
is a diagram of the circuit
50
a
in the current-to-voltage converting circuit
50
. As the four circuits
50
a
to
50
d
are identical in construction, the action of the circuit
50
a
will representatively be described.
The current signal I
31
a
from the photo receiver
31
a
is received by a terminal P
1
. The received signal is then converted to a voltage signal by a differential amplifier composed of a pair of transistors Q
1
and Q
2
. A pair of transistors Q
4
and Q
5
act as a load of the differential amplifier. A voltage at the collector of the transistor Q
1
is fed back via a transistor Q
7
and a resistor Rf to the base of the transistor Q
1
. Degree of the conversion of the current signal to the voltage signal in the circuit
50
a
does not depend on the amplifying factor of each transistor but is determined by the resistor Rf. The voltage signal converted from the current signal is then released as a reference voltage Vc from a terminal P
2
. A capacitor Cf is used for attenuating poles generated by a parasitic capacitance in the resistor Rf and so on. The base of the transistor Q
2
is connected with the reference voltage Vc of the circuit. A voltage between Vcc and GND is 5 V, and a voltage between Vc and GND is 2.5 V. The idling current Ic
0
supplied from a current source I
0
to the differential amplifier is 1500 &mgr;A (The idling current is a collector current which flows the transistor when no signal is input).
Commonly for reproducing data, a DVD-ROM is rotated at 3.49 m/s of linear velocity and a 4.7 GB DVD-RAM is rotated at 8.2 m/s of linear velocity. In a data reproducing apparatuses using DVD-ROM, a technology for rapidly reading data has been developed, and the apparatus are commercialized which can read data substantially 10 or more times faster than an initial products having linear velocity of 3.49 m/s. However, when DVD-RAM is reproduced in such an apparatuses which can reproduce the data faster, there is a problem that the data may not be read accurately since signal-to-noise ratio of the DVD-RAM is lower than that of DVD-ROM. That is, as there is a difference in the optical properties between DVD-ROM and DVD-RAM, it is hard to realize stable reading operation to both types of the recording media.
SUMMARY OF THE INVENTION
It is thus an object of the present invention, for eliminating the foregoing drawback and realizing both of the rapid reproduction of DVD-ROM and the stable reproduction of DVD-RAM. The object also is to provide a current-to-voltage converting circuit which is simple in construction and can produce less noises, and an optical pickup head apparatus using such a current-to-voltage converting circuit. It is another object of the present invention to provide an apparatus for recording or reproducing data using the optical pickup head apparatus, and a method of recording or reproducing data implemented with the current-to-voltage converting circuit.
In a first aspect of the invention, a current-to-voltage converting circuit is provided which receives a current signal output from a photodetector outputting a current signal according to amount of received light and converts the received current signal into a voltage signal. The circuit comprises an active element applied with a negative feedback, and a variable current section for varying an idling current which is to be supplied to the active element in accordance with a level of the current signal received from the photodetector or a reproduction speed of the data.
In a second aspect of the invention, a current-to-voltage converting circuit is provided which comprises a current-to-voltage converter which receives a current signal output from a photodetector outputting a current signal according to amount of received light and converts the received current signal into a voltage signal, the current-to-voltage converter comprising an active element applied with a negative feedback, a dummy circuit which has the same structure as the current-to-voltage converter and receives no current signal from the photodetector, a differential operator for performing a differential operation between a signal output from the dummy circuit and a reference signal, a operating section for performing a differential operation or an adding operation, using the voltage signal from the
Wenderoth , Lind & Ponack, L.L.P.
Zweizig Jeffrey
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