JPS61158042A - Tracking controlling circuit - Google Patents

Abstract

PURPOSE:To enable accurate and stable tracking control by finding the difference between two light receiving means, detecting DC offset in the input/output system of the two light receiving means from input signals and output signals of a differential amplifier, supplying the detection signal to the differential amplifer and canceling the offset. CONSTITUTION:For instance, if there is a difference in sensitivity between photodiodes 21 and 31, the DC level of output of amplifiers 4 and 5, which is intrinsically fixed, fluctuates. Consequently, a tracking error signal on which a DC offset signal d is superposed appears in an output of a differential ampli fier 6. An output of the differential amplifier 6 is inputted to a low-pass filter 7. As a time constant of a resistance 71 and a capacitor 72 of the low-pass filter 7 is selected to cut off an intrinsic tracking error signal component which is an AC component, only a DC offset signal (d) is outputted. As the signal d is inputted to an invertion terminal of an operational amplifier 64 through a resistance 66, a tracking error signal in which the DC offset is canceled is outputted from the differential amplifier 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tracking control circuit in an optical information recording/reproducing device such as an optical video disc player or a digital audio disc player.

[Conventional technology]

In an optical information recording/reproducing device such as an optical video disc player, information is recorded/reproduced by irradiating a disc as an information recording medium with a laser beam or the like. In this case, tracking control is performed so that the light follows the track on the disk. Although various methods have been proposed for such tracking control, a method called the 3-beam method has been put into practical use because it allows stable control.

In this method, one beam is used for recording and reproducing information, and the other two beams are used for recording and reproducing information.
Two beams for tracking are placed on both sides of the beam for recording and reproducing information.

Therefore, the light receiving means for receiving the three beams is arranged as shown in FIG. 5, for example. In the figure, 1 is a light receiving means for receiving a beam for information recording and reproduction, and 2 and 3 are light receiving means for receiving a tracking beam. The light receiving means 1 is divided into four parts in order to perform focus control using a method called the astigmatism method. Since the principle is well known, detailed explanation will be omitted.

FIG. 6 represents a block diagram of a tracking control circuit according to such a method. That is, the outputs of the light receiving means 2.3 are each amplified by amplifiers 4.5, and the outputs are further supplied to a differential amplifier 6.

A tracking error signal is generated by taking the difference between the two, and tracking control is performed based on this signal.

To explain the operation with reference to FIG. 7, the output signal (a) of the amplifier 4 (light receiving means 2) and the output signal (a) of the amplifier 5 (light receiving means 3)
Output signal (b) means that when the recording/reproducing beam deviates from the track on the disk, one level increases from the predetermined DC level and the other level increases from the predetermined DC level in response to the direction. The relationship is decreasing (opposite phase). Therefore, the output (c) of the differential amplifier 6, which is the difference between the two, becomes an alternating current signal (tracking error signal) because the DC levels of the two are cancelled.[Problem to be solved by the invention] However, the light receiving means 2 3 has a DC offset, for example, there is a difference in sensitivity between the light receiving means 2 and 3, a difference in DC gain between the amplifiers 4 and 5, or a difference in the intensity of the two tracking beams. If so, as shown in FIG.
This has the disadvantage that a direct current offset signal d is generated, making it impossible to perform accurate tracking control.

[Means for solving problems]

FIG. 1 shows a block diagram of the tracking control circuit of the present invention. In this figure, parts corresponding to those in FIGS. 5 and 6 are denoted by the same reference numerals, and detailed description thereof will be omitted (the same applies hereinafter).

That is, in the present invention, the outputs of the two light receiving means 2.3 are amplified by the amplifier 4.5, the difference between the outputs is obtained by the differential amplifier 6, and the difference between the output and the input of the differential amplifier is A low-pass filter 7 is connected to.

FIG. 2 shows a more detailed circuit diagram of the tracking control circuit shown in FIG. In other words, the light receiving means 2 is composed of a photodiode to which a predetermined potential is applied to its cathode and whose anode is grounded via a resistor 22, and the amplifier 4 has a signal input to its inverting terminal via a resistor 41. It is.

An operational amplifier 42 whose non-inverting terminal is grounded, and a feedback resistor 42 is connected between its output terminal and its inverting terminal.
It is made up of. Similarly, photodiode 3
1 and the resistor 32, the light receiving means 3 is connected to the resistor 51.5.
2 and an operational amplifier 53 constitute an amplifier 5, respectively. The differential amplifier 6 includes an input resistor 61 to an inverting terminal, an input resistor 63 to a non-inverting terminal. A feedback resistor 62 connected between the output terminal and the inverting terminal, and a resistor 65 that grounds the non-inverting terminal. Furthermore, it is composed of an operational amplifier 64 having a signal input resistor 66 for offset adjustment.

Furthermore, the low-pass filter 7 includes a resistor 71 and a capacitor 72.
It is composed of.

[Effect]

The effect will now be explained. For example, if there is a difference in sensitivity between the photodiodes 21 and 31, the DC level of the outputs of the amplifiers 4 and 5, which should originally be constant, fluctuates as shown in FIGS. 8(a) and 8(b). As a result, a tracking error signal on which the DC offset signal d is superimposed appears at the output of the differential amplifier 6, as shown in FIG. 8(c). The output of this differential amplifier 6 is input to a low pass filter 7. The low pass filter 7 is.

Since the time constants of the resistor 71 and capacitor 72 are selected so as to block the original tracking error signal component, which is an AC component, only the DC offset signal d is output. This signal d is passed through a resistor 66 to an operational amplifier 64.
Since the tracking error signal is input to the inverting terminal of the differential amplifier 6, a tracking error signal as shown in FIG. 7(c) with the DC offset canceled is output from the differential amplifier 6.

〔Example〕

FIG. 3 represents another embodiment of the invention.

That is, in this embodiment, the outputs of amplifiers 4 and 5 are input to a differential amplifier 8 to obtain a difference signal between the two, and the output of the difference signal is input to a differential amplifier 6. FIG. 4 shows a more detailed circuit diagram of FIG. 3, and the differential amplifier 8 includes an input resistor 81, 82, a parallel circuit of a resistor 84 and a capacitor 85 whose non-inverting terminal is grounded, and an output terminal. A resistor 86 and a capacitor 8 connected between the inverting terminal and
It is composed of an operational amplifier 83 having seven parallel circuits. In this embodiment, a DC offset signal d is detected by a differential amplifier 8 having an integrating function and is supplied to a differential amplifier 6.

〔effect〕

As described above, in the present invention, the difference between the outputs of the two light receiving means is taken, and the DC offset in the input/output system of the two light receiving means is detected from the input signal or output signal of the differential amplifier that outputs the tracking error signal. However, since the detection signal is supplied to the differential amplifier to cancel the offset, accurate and stable tracking control can be realized with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the tracking control circuit of the present invention,
Fig. 2 is a more detailed circuit diagram thereof, Fig. 3 is a block diagram of another embodiment, Fig. 4 is a more detailed circuit diagram thereof, and Fig. 5 is a more detailed circuit diagram thereof.
This figure is a schematic plan view of the light receiving means, FIG. 6 is a block diagram of a conventional tracking control circuit, and FIGS. 7 and 8 are waveform diagrams thereof. 1.2.3... Light receiving means 4.5... Amplifier 6.8... Differential amplifier 7... Low pass filter or higher

Claims (3)

[Claims] (1) A first light receiving means, a second light receiving means, a first amplifier that amplifies the output of the first light receiving means, and a second amplifier that amplifies the output of the second light receiving means. , a differential amplifier that outputs the difference between the output of the first amplifier and the output of the second amplifier, and tracking control of light irradiated onto the information recording medium in accordance with the output of the differential amplifier. In a tracking control circuit that performs A tracking control circuit characterized by detecting a direct current offset between the first light receiving means and the second light receiving means and supplying the detected signal to the input of the differential amplifier. (2) The DC offset between the first light receiving means and the second light receiving means is detected by a low-pass filter from the output signal of the differential amplifier. Tracking control circuit. (3) The DC offset between the first light receiving means and the second light receiving means is detected by another differential amplifier from an input signal to the differential amplifier. The tracking control circuit according to item 1.