Tracking error balance adjustment circuit and a current control circuit used for an optical disk playback apparatus, and an optical disk playback apparatus including the same

• US 6,504,799 B1
• Filed: 03/10/2000
• Issued: 01/07/2003
• Est. Priority Date: 03/12/1999
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Haga, Hiroyuki, Yamashita, Ryuichi, Murai, Shinobu
• Primary Examiner(s): Hindi, Nabil
• Application Number:
  US09/523,284
• Time in Patent Office: 1,033 Days
• Field of Search: 369/44.27, 369/44.29, 369/44.28, 369/44.11, 369/124.01
• US Class Current: 369/44.11
• CPC Class Codes: G11B 7/0903 Multi-beam tracking systems
• CPC Class Codes: G11B 7/094 Methods and circuits for servo offset compensation
• CPC Class Codes: G11B 7/0941 Methods and circuits for servo gain or phase compensation during operation for initialising servos G11B7/0945

Abstract

A tracking error balance adjustment circuit, and a current control circuit used for a variable gain RF amplifier automatically controlled to output a signal having a predetermined amplitude. The tracking error balance adjustment circuit comprises two separate gain adjusting circuits, each having variable attenuation circuit having first gm amplifier of variable gm type, a second gm amplifier of variable gm type connected to the variable attenuation circuit, and an output circuit connected to the second gm amplifier, comprising an operational amplifier circuit having feedback resistor, wherein the first and second gm amplifiers are differentially controlled commonly by a control current. The a current control circuit is arranged in a variable gain RF amplifier connected to a head amplifier circuit amplifying an output signal from optical pickup, controlling a current output of the variable gain RF amplifier so that it changes in accordance with different functions in the range where the control voltage input is lower than the reference potential and the range where the control voltage input is higher than the reference potential, with the result that the gain control sensitivity can be set almost equal between the two ranges.

Claims

1. A tracking error balance adjustment circuit for correcting at least one of first and second signals in level to set a level difference between the first and second signals to substantially zero when an irradiation position of a laser beam emitted by an optical pickup substantially coincides with a track center wherein a tracking error signal is generated in accordance with the level difference between the first and second signals that complementarily change in level in accordance with a deviation of the irradiation position of the laser beam from the track center in order to detect a shift of the irradiation position of the laser beam from a track which holds information on an optical disk, said tracking error balance adjustment circuit comprising:

a current control circuit receiving a tracking error balance adjustment voltage and converting the tracking error balance adjustment voltage into a control current;

a gain control circuit receiving said first signal, said second signal, and said control current, adjusting at least one of said first signal and said second signal in level, and outputting said first signal and said second signal, said gain control circuit comprising at least two signal paths each of which has a plurality of gm amplifiers of variable transconductance type, said plurality of gm amplifiers in the same signal path having transconductances controlled differentially in accordance with the control current from said current control circuit;

the two signal paths having a first gain control circuit and a second gain control circuit, respectively;

the first gain control circuit having a first gm amplifier of variable transconductance type, and a second gm amplifier of variable transconductance type, the transconductances of the first and second gm amplifiers being controlled differentially in accordance with the control current from the current control circuit, thereby to adjust the first signal in level;

the second gain control circuit having a third gm amplifier of variable transconductance type, and a fourth gm amplifier of variable transconductance type, the transconductances of the third and fourth gm amplifiers being controlled differentially in accordance with the control current from the current control circuit, thereby to adjust the second signal in level; and

the tracking error signal generated by differentially adding an output from the first gain control circuit and an output from the second gain control circuit.

2. A circuit according to claim 1, wherein:

the first gain control circuit comprises;

a first variable attenuation circuit including an impedance element connected to an input node of the first gain control circuit, and the first gm amplifier of variable transconductance type connected to an output of the impedance element;

the second gm amplifier of variable transconductance type connected to an output of the first variable attenuation circuit; and

an operational amplifier circuit connected to an output of the second gm amplifier, and having a feedback resistive element connected between input and output terminals thereof,

the second gain control circuit comprises;

a second variable attenuation circuit having an impedance element connected to an input node of the second gain control circuit, and the third gm amplifier of variable transconductance type connected to an output of the impedance element;

the fourth gm amplifier of variable transconductance type connected to an output of the second variable attenuation circuit; and

an operational amplifier circuit connected to an output of the fourth gm amplifier, and having a feedback resistive element connected between input and output terminals thereof, and

a pair of the first gm amplifier and the fourth gm amplifier and another pair of the second gm amplifier and the third gm amplifier are controlled in common in each pair in accordance with the control current, the pairs are controlled differentially in a manner such that when the transconductances of the gm amplifiers are increased in one of the pairs, the transconductances of the gm amplifiers are decreased in the other of the pairs.

3. A circuit according to claim 1, wherein:

each of the gm amplifiers comprises a differential pair of bipolar transistors having emitters connected in common to a gain control input node, and having bases for respectively receiving a reference voltage and an input signal.

4. A circuit according to claim 1, wherein:

the first gain control circuit and the second gain control circuit are controlled differentially by the control current, such that when a gain of one of the first gain control circuit and the second gain control circuit is increased, a gain of the other of the first gain control circuit and the second gain control circuit is decreased.

5. A circuit according to claim 1, wherein:

the current control circuit comprises;

a differential pair of PNP transistors;

a first current source and a second current source respectively connected between each of emitters of the differential pair of PNP transistors and a power supply node;

a resistive element connected between the emitters of the differential pair of PNP transistors;

a first NPN transistor connected between a collector of one of the differential pair of PNP transistors and a ground potential, and having a collector and a base connected to each other;

a second NPN transistor connected between a collector of the other of the differential pair of PNP transistors and the ground potential, and having a collector and a base connected to each other;

a third NPN transistor current-mirror-connected to the first NPN transistor and having a collector connected to a gain control input node of one of the plurality of gm amplifiers of variable transconductance type in the same current path; and

a fourth NPN transistor current-mirror-connected to the second NPN transistor, and having a collector connected to a gain control input node of another of the plurality of gm amplifiers of variable transconductance type in the same current path.

6. A semiconductor integrated circuit employed in an optical disk playback apparatus having a tracking control servo mechanism, the semiconductor integrated circuit comprising:

a tracking error signal generation circuit which generates a tracking error signal, and which includes a tracking error balance adjustment circuit according to claim 1,

wherein the tracking control servo mechanism controls an irradiation light from an optical pickup in position on an optical disk in the radial direction thereof, in accordance with an output from the tracking error signal generation circuit, there by to control the irradiation light from the optical pickup to be kept on a track.

7. A tracking error balance adjustment circuit for correcting at least one of first and second signals in level to set a level difference between the first and second signals to substantially zero when an irradiation position of a laser beam emitted by an optical pickup substantially coincides with a track center wherein a tracking error signal is generated in accordance with the level difference between the first and second signals that complementarily change in level in accordance with a deviation of the irradiation position of the laser beam from the track center in order to detect a shift of the irradiation position of the laser beam from a track which holds information on an optical disk, said tracking error balance adjustment circuit comprising:

a current control circuit receiving a tracking error balance adjustment voltage and converting the tracking error balance adjustment voltage into a control current;

a gain control circuit receiving said first signal, said second signal, and said control current, adjusting at least one of said first signal and said second signal in level, and outputting said first signal and said second signal, said gain control circuit comprising at least two signal paths each of which has a plurality of gm amplifiers of variable transconductance type, said plurality of gm amplifiers in the same signal path having transconductances controlled differentially in accordance with the control current from said current control circuit;

wherein;

the current control circuit comprises;

a differential pair of PNP transistors;

a first current source and a second current source respectively connected between each of emitters of the differential pair of PNP transistors and a power supply node;

a resistive element connected between the emitters of the differential pair of PNP transistors;

a first NPN transistor connected between a collector of one of the differential pair of PNP transistors and a ground potential, and having a collector and a base connected to each other;

a second NPN transistor connected between a collector of the other of the differential pair of PNP transistors and the ground potential, and having a collector and a base connected to each other;

a third NPN transistor current-mirror-connected to the first NPN transistor and having a collector connected to a gain control input node of one of the plurality of gm amplifiers of variable transconductance type in the same current path; and

a fourth NPN transistor current-mirror-connected to the second NPN transistor, and having a collector connected to a gain control input node of another of the plurality of gm amplifiers of variable transconductance type in the same current path.

8. A tracking error balance adjustment circuit comprising:

a first current-to-voltage conversion circuit to which a first signal detected in accordance with a deviation of an irradiation position of a laser beam to a track of an optical disk is supplied;

a second current-to-voltage conversion circuit to which a second signal detected in accordance with a deviation of an irradiation position of the laser beam to the track of the optical disk is supplied, a level of the second signal complementarily changing to the level of the first signal;

a current control circuit receiving a tracking error balance adjustment voltage and converting the tracking error balance adjustment voltage into first and second control currents, said first and second control currents complementarily changing in level;

a first pair of amplifiers including a first amplifier to which an output voltage from the first current-to-voltage conversion circuit is supplied, and a second amplifier to which an output voltage from the second current-to-voltage conversion circuit is supplied;

a second pair of amplifiers including a third amplifier to which the output voltage from the first current-to-voltage conversion circuit is supplied, and a fourth amplifier to which the output voltage from the second current-to-voltage conversion circuit is supplied;

a gain of at least one of said first and second pairs of amplifiers being variably controlled differentially in accordance with the first and second control currents from the current control circuit; and

an addition circuit to which the output signals of said third and fourth variable gain amplifiers are supplied, said addition circuit adding the output signals of said third and fourth variable gain amplifiers and generating a tracking error signal.

9. The tracking error balance adjustment circuit according to claim 8, comprising:

said first amplifier comprising a first variable gain amplifier to which an output voltage from the first current-to-voltage conversion circuit is supplied, a gain of said first variable gain amplifier being controlled in accordance with the first control current supplied from the current control circuit;

said second amplifier comprising a second variable gain amplifier to which an output voltage from the second current-to-voltage conversion circuit is supplied, a gain of said second variable gain amplifier being controlled in accordance with the second control current supplied from the current control circuit;

said third amplifier comprising a third variable gain amplifier to which the output voltage from the first current-to-voltage conversion circuit is supplied, a gain of said third variable gain amplifier being controlled in accordance with the second control current supplied from the current control circuit; and

said fourth amplifier comprising a fourth variable gain amplifier to which the output voltage from the second current-to-voltage conversion circuit is supplied, a gain of said fourth variable gain amplifier being controlled in accordance with the first control current supplied from the current control circuit.