JPS60113334A - Method for detecting optical signal in optical disk device - Google Patents

Abstract

PURPOSE:To prevent entirely adverse influences to be exerted on a servo signal even when input impedance is made very low to obtain a high S/N for an amplifier for main signal by operating a photodetecting element as a constant current source, separating a servo system and a main signal system by the light detecting element and outputting. CONSTITUTION:Signal current that flows in the direction of the arrow of solid line of main signal detected by photodetecting elements 8a, 8b, 8c, 8d is added by an amplifier 13 for adding and sent to a regenerative circuit due to characteristic that the amplifier 13 for adding is low input impedance type of current feedback. At this time, even when the capacity of a capacitor 12, separation is made perfectly by photodetecting elements 8a, 8b, 8c, 8d. Servo signals detected by light detecting elements 8a, 8b, 8c, 8d are sent to a focus and tracking correction controlling circuit through respective amplifier 15a, 15b, 15c, 15d. The servo signals at this time give no influence to the main signal side.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an optical signal detection method in an optical disk device.

Generally, in optical disk memories, optical video disks, compact disks, etc., as shown in Fig. 1, a track (2) is formed on a disk (1) in units of μm, and a track (2) is formed facing this track (2). 1 photodetector (3)
The laser beam (4) is used to obtain both main signals such as video, audio, and data, and servo signals such as track servo and focus servo. The main signal is sent to the CRT (6) via the reproducing circuit (5), and the servo signal is returned to the photodetector (3) via the servo circuit (7) for focus and track control. be.

However, in a disk head amplifier, it is desirable to process the main signal at a high S/N and the servo signal at a high level, but with conventional circuits, it is impossible to satisfy both with a single circuit. Yes, I had to sacrifice one or the other. Specifically, as shown in FIG. 2, the conventional photodetector (3) is composed of four-divided photodetecting elements (8a) (8b) (8c) consisting of photodiodes.
(8d) to the respective resistances (9a) (9b) (9c
) (9d) in series and then in parallel with each other, one end of each is grounded, the other end is connected to the power terminal (10B) via a resistor (10), and the photodetector element (
8a) (8b) (8c) (8d) and resistor (9a)
Connection point (lla) of (9b) (9c) (9d) (
llb) (llc) (Ltd) is the capacitor (12
a) (12b,) (12c) (12d), coupled to the output terminal (14) via a low input impedance summing amplifier (13) to output a main signal (for example, a frequency-modulated video signal); The connection point (Ila) (l
lb) (llc) (lid) are output terminals (16a) (16b) (16c) (
16d) to output a servo signal.

In such a configuration, when trying to detect the addition spectrum band including low frequencies as the output signal of the addition amplifier (13) in order to improve the reproducibility of the digital waveform, the capacitors (+2a) (12b) ( 12c) (12
d) capacity must be increased. More specifically, for writable discs, 500KIlz~I
Since it contains a MHz track address signal, it is necessary to read it accurately, and for compact discs, it is required to read it as a pulse waveform. Therefore, as mentioned above, a large capacitance capacitor is required.

At this time, the output impedance of the servo system is a resistance (9a
) to (9d), and since the input impedance of the summing amplifier (13) is very low to improve the S/N, the servo system becomes an equivalent circuit as shown in Figure 3, and 0
In the low frequency servo signal range of ~10 KHz, level fluctuations and phase rotation occur, which adversely affect focus and tracking correction.

The present invention was made in order to solve the conventional problems as described above, and consists of operating a photodetection element such as a photodiode as a constant current source, and connecting the servo system and main signal system to the photodetection element (internal impedance). is infinity) and output it separately.

An embodiment of the photodetection method according to the present invention will be described below with reference to the drawings.

First, the present invention will be explained in detail based on FIG. ), which prevents recombination. Therefore, these electrons will flow regardless of the value of the coupled load (resistance). In other words, this can be thought of as a current source that uses the intensity of light (laser) as a signal.

The internal impedance of a current source is generally considered to be approximately infinite. Therefore, in FIG. 4, the resistance (10
), photodetector (8), and resistor (9) in series circuit, A
Points A and B generate the same signal voltage with respect to ground potential, but both points A and B are completely separated, and no matter what load is applied to both points A and B, they influence each other. That is not the case at all.

The present invention has been made based on the above principle, and a specific circuit will be explained based on FIG. 5.

Resistors (9a) (9b) (9c) are installed on the anode side of each photodetector element (8a) (8b) (8c) (8d), which is composed of a photodiode and is divided into four parts.
) (9d) in series, and these resistors (9a)
(9b) (9c) The other end on the (9d) side is grounded, and the photodetector element (8a) (8b) (8c) (8d
) are connected to each other at one point, and then resistor ( ]
0) to the reverse bias power supply terminal (V). Further, a capacitor (17) is inserted between this reverse bias power supply terminal (V) and ground.

Each of the photodetecting elements (8a) (8b) (8c
) (8d) are equipped with servo signal amplifiers (15a) (15b) (15c) (15d), respectively.
) via the servo signal output terminal (16a) (1,6b
) (16c) (16d) are combined. Also,
The photodetector elements (8a) (8b) (8c) (8d
), there is a capacitor (12) on the cathode side that meets one point.
, are coupled to the main signal output terminal (14) via a low input impedance type summing amplifier (13).

In the above configuration, each photodetector element (8a) (8b) (8c) (
The main signal detected in step 8d) is added to the signal current flowing in the direction of the solid arrow shown in the figure by the addition amplifier (13) and sent to the reproducing circuit. At this time, the capacitor (12
) Even if the capacitance of ) is large, the photodetection element (8a) (8b)
(8c) Completely separated in (8d).

In addition, each photodetector element (8a) (8b) (Be) (
The servo signal detected at 8d) is sent to each amplifier (8d).
15a) (15b) (15c) (], 5d) to the focus and tracking correction control circuit. The servo signal at this time also does not affect the main signal side.

Since the present invention employs the method described above, the main signal and the servo signal are detected by the same photodetecting element.

Even if the input impedance of the main signal amplifier is made very low in order to obtain a high S/N ratio, the servo signal will not be adversely affected at all. Furthermore, the circuit configuration is simple and can be provided at low cost.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an optical disk device, FIG. 2 is an electric circuit diagram of a conventional photodetection circuit, FIG. 3 is an equivalent circuit diagram of the servo system circuit part in FIG. 2, and FIG. FIG. 5 is a diagram showing the principle of the signal detection method, and is a specific diagram of the optical signal detection circuit. (1)...Disc, (2)...Track, (3)
...Photodetector, (4)...Laser light, (5)...
Reproduction circuit, (6)...CRT, (7)--Servo circuit, (8) (8a) (8b) (8c) (8d)-
Photodetection element, (9) (9a) (9b) (9c)
(9d) (10) - resistance, (lla) (]lb) (
lie) (lid) - connection point, (12) (1,2a)
(1, 2b) (12c) (12d) (17)... Capacitor, (13)... Main signal addition amplifier, (14
)--Main signal output terminals, (15a) (15b) (
15c) (15d) - = servo signal amplifier, (16
) (16a) (16b) (16c) (16d)... Servo signal output terminal. Applicant General Co., Ltd. Figure 1 Figure 3

Claims (1)

[Claims] (1) Irradiate the optical disk with a laser beam and use the same photodetector to obtain the main signal and servo signal from the reflected light.The main signal is sent to the amplifier for main signal processing, and the servo signal is sent to the amplifier for servo signal processing. In an optical signal detection circuit designed to send to. The photodetecting element consists of a photodiode, and in order to use this photodetecting element as a current source, a reverse bias voltage is applied through a resistor, a main signal is output from the cathode side of the photodetecting element, and a servo signal is output from the anode side. An optical signal detection method in an optical disk device that outputs a signal. (2. In claim 1, the photodetecting element is composed of a photodiode divided into four parts, and a circuit in which a resistor is connected in series to each photodetecting element is connected in parallel to each other, and each photodetecting element is divided into four parts. An optical signal detection method in an optical disk device in which the signals on the anode side are added together to output a main signal, and the signals on the cathode side of each photodetection element are output as individual servo signals.