JPS58200434A - Detecting circuit for tracking error signal of optical disk player - Google Patents

Abstract

PURPOSE:To obtain the titled circuit with high reliability at low cost, by making the feedback resistance which is connected from the output of an operational amplifier to the negative-phase input coincide with the resistance which is grounded from the positive-phase input then detecting the output of each photodetector of positive-phase and negative-phase inputs respectively. CONSTITUTION:The current of a photodetector 6 is obtained in the form of voltage at an output 18 by a resistance 20 and an operational amplifier 19. If the current of the detector 6 flows toward the resistance 20, the voltage of the output 18 is negative and the voltage value is equal to a product of the current value of the detector 6 and the resistance value of the resistance 20. While the current of a photodetector 7 is converted into voltage by a resistance 21 and obtained at the output 18 via the amplifier 19. If the current of the detector 17 flows toward the resistance 21, the voltage of the output 18 is positive and the voltage value is equal to a product of the current value of the detector 7 and the resistance value of the resistance 21. As a result, the voltage obtained by giving a current-voltage conversion and a subtraction between current outputs of detectors 6 and 7 is obtained at the output 18. Thus it is possible to obtain a detecting circuit with high reliability at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking difference signal detection path for obtaining a voltage corresponding to a deviation from a signal track of an optical disc player.

FIG. 1 shows a principle diagram of tracking error signal detection to which the present invention relates. 1 is a signal track where unevenness information is recorded, 2 is a portion where information is not recorded between signal tracks,
6 is a spot on the disc of laser light from the pickup of an optical disc player, and is the main spot for reading unevenness information from signal track 1. 4 and 5 are also spots on the disc of laser light from the pickup of an optical disc player, and are main spots. This is a sub-spot for detecting a tracking error signal for making the signal track 5 follow the signal track. Tracking error signal detection am is side spot 4
This is called a 5-spot method in which the amount of light reflected from the side spot 5 and the side spot 5 is converted from light to current using each photodetector, the current is converted to voltage, and the difference is extracted. As shown in Figure 1, if the main spot 3 is shifted to the left from the signal track 1, the side spot 4 will be on top of the signal track 1, and the side spot 5 will be on the top of the signal track 1. The number of so-called mirror surfaces 2 between the signal tracks 10 increases considerably.

On the other hand, in region 2, most of the laser light is reflected by #1,
In signal track 1, the amount reflected is smaller than in area 2. As a result, in case 19), the reflected light from side spot 4 is smaller than the reflected light from side spot 5, and when the photodetector output of side spot 5 is subtracted from the photodetector output of side spot 4, becomes a negative value. In the case shown in Figure 1, the main spot 3 is aligned with the signal track 1, and the side spots 4 and 5 are irradiated onto the signal track 1 and area 2 by the Okajiyo 5, so the side spot 4 is The reflected lights from and 5 are the same, and when the photodetector output of side spot 5 is subtracted from the photodetector output of side spot 4, it becomes zero. Also the first
As shown in Figure (c) K, when the main spot 3 is shifted in the opposite direction to No. 117 (a), the reflected light from the side spot 4 is greater than the reflected light from the side spot 5, and the light from the side spot 4 is Subtracting the photodetector output of side spot 5 from the detector output yields a positive value iJI<.

As explained above, the value obtained by subtracting the photodetector output of side spot 5 from the photodetector output of side spot 4 becomes a positive value when main spot 3 shifts to the right from signal track 1 in FIG. If it deviates, it will show a negative value, so
If the value is controlled to be zero, the main spot 3 can be made to follow the signal track IK.

Conventionally, the circuit shown in FIG. 2 has been widely used to detect this tracking error signal. 6 and 7 are side spots 4
and a photodetector that detects the reflected light from 5, 8 is a power supply that applies an operating bias to the photodetector, and ! , 10 and 11 are operational amplifiers, 12 to 17 are resistors, and 18 is a tracking error signal output. Operational amplifiers for the outputs of photodetectors 6 and 7? h low resistance 2, operational amplifier 10 and resistor 15
Converts the current to voltage, and then converts the operational amplifier 11 and resistor 14.
A tracking error signal is obtained at output 18 by subtracting .about.17.

However, it is redundant to use three operational amplifiers to obtain the output difference between the photodetectors 6 and 7.

SUMMARY OF THE INVENTION An object of the present invention is to provide a simple current-voltage conversion and subtraction circuit that can be used to detect tracking error signals in optical disc players.

Therefore, in the present invention, the feedback resistor connected from the output of the operational amplifier to the negative phase input and the resistor connected from the positive phase input to ground are set to -j-, and the respective photodetector outputs are connected to the positive phase input and the negative phase input. The reason is that the circuit has been simplified.

An embodiment of the present invention is shown in FIG. In this figure, the same reference numerals as in FIG. 2 indicate the same functions.

10 is an operational amplifier, and 20 and 21 are resistors.

The current of the photodetector 6 is obtained as a voltage at the output 18 by a resistor 20 and an operational amplifier 19. The current of the photodetector 6 is connected to the resistor 20
If the current flows in the direction of , the voltage of the output 18 will be negative, and the voltage 11 will be the product of the current value of the photodetector 6 and the resistance value of the resistor 20. On the other hand, the current of the photodetector 7 is converted into a voltage by a resistor 21, and then passed through an amplifier with a gain of 1 consisting of an operational amplifier 19 and a resistor 20, and then outputted as an output 11K1. Photodetector 7
If the current flows in the direction toward the resistor 21, the voltage of the output 18 will be positive, and the direct voltage value will be the product of the current value of the photodetector 7 and the resistance value of the resistor 21. As a result of the above photodetector 6
The current output of and 7 is converted into a current voltage and the subtracted voltage is obtained at the output 18.

K, which changes the ratio of tt' subtraction, can be done by changing the ratio of resistors 20 and 21. For example, if there is variation in the photodetection sensitivity of the photodetectors 6 and 7, adjustment can be made by making the resistor 20 or 21 a variable resistor. An example thereof is shown in FIG. 22 is a variable resistor. If the sensitivity of photodetectors 6 and 7 is not determined, use variable resistor 2.
The resistance value of resistor 2 is set so that it can be adjusted to be larger and smaller than resistor 20. Note that this embodiment uses the resistor 21 in FIG.
Although the variable resistor 22 is inserted in place of the resistor 20, the same effect can be obtained even if a variable resistor is inserted in place of the resistor 20.

A band-limited circuit diagram as another embodiment of the present invention is shown in FIG. 5, and 23 and 24 are capacitors.

The current of the photodetector B is converted into a voltage by the impedance determined by the resistor 20 and the capacitor 23, while the current of the photodetector 7 is converted to voltage by the impedance of the resistor 21 and the capacitor 24, so the output 18 has a high frequency range. This results in continuous characteristics.

As described above, according to the present invention, since the circuit for obtaining the tracking error signal of the optical disc player has a small number of components, it is possible to obtain a highly reliable circuit at low cost.

[Brief explanation of drawings]

Fig. 1 shows the principle of tracking error detection, Fig. 2 is a conventional circuit diagram, Fig. 5 is a circuit diagram of an embodiment of the present invention, Fig. 4 is a circuit diagram of another embodiment of the invention, and Fig. FIG. 5 is a circuit diagram of still another embodiment of the present invention. 6.7... Photodetector 19... Operational amplifier 20,
21...Resistor 22...Variable resistor 23.24.
... Capacity O 1 圀 (υ) (b) (C) t 2 Figure t 3 Pusaito Figure S Figure

Claims (1)

[Claims] 1. In an optical disk player that optically reads a signal in which concave and convex information is recorded in a spiral shape or concentrically on a disc, the first and second discs have actual currents that change in opposite directions depending on the deviation from the signal track. 2 photodetectors and operational amplifiers, the output of the first photodetector is connected to the negative phase input of the operational amplifier; and the output of the second photodetector is connected to the positive phase input of the operational amplifier; and a resistor is connected between the positive phase input of the operational amplifier and ground and between the output of the operational amplifier and the negative phase input, respectively, and a tracking error voltage is obtained at the output of the operational amplifier. Tracking error signal detection circuit.