JPS63171458A - Magneto-optical medium reproducing circuit - Google Patents

Abstract

PURPOSE:To prevent the deterioration in performance due to temperature changes or secular changes by splitting reflected or regenerated light from a magneto-optical medium into two optical paths, converting its current difference directly to eliminate in-phase noise components. CONSTITUTION:A regenerated information signal from a magneto-optical medium is split into two optical paths depending on the difference from the polarized face and the amplification factor of an avalanche photodiode 32 is adjusted by a reverse bias voltage control circuit 35 to make two DC components equal to each other thereby eliminating the in-phase noise components. Since the differential amplifier 12 is constituted to extract the output in response to the difference of the DC component, automatic control for bringing the output of differential amplifier 12 to zero is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a reproducing circuit for a magneto-optical medium reproducing apparatus that reproduces signals recorded on a magneto-optical medium.

(Prior Art) Conventionally, as a reproducing circuit of a magneto-optical medium reproducing apparatus, one using a differential amplifier circuit (for example, Japanese Patent Application Laid-Open No. 60-223045) is known, and its configuration is as shown in FIG.

In FIG. 2, reference numeral 21 denotes a magneto-optical recording medium, which is formed by recording, for example, Mn on a substrate made of glass, plastic, or the like.

A magneto-optical material such as Bi is sputtered or vapor deposited,
Information signals are recorded according to the perpendicular magnetization direction (upward or downward) recorded on the recording track. Further, the magneto-optical recording medium 21 is rotated at a constant speed by a motor (not shown) during reproduction.

A signal detection optical system for optically reading information recorded on the magneto-optical medium 21 includes a semiconductor laser 22 as a light source for irradiating a beam spot onto the magneto-optical recording medium 21, and a collimator lens 23 that converts the laser light output into a parallel light beam, and a polarizer 2 that linearly polarizes the parallel light beam from the collimator lens 23.
4, a beam splinter 25 that transmits a part of the linearly polarized light (S-polarized light) by the polarizer 24 and reflects the rest; It includes a condenser lens 26 that connects a beam spot to the recording surface of the recording medium 21. Note that the polarizer 24 may be omitted if the degree of linear polarization of the mountain light from the light source is sufficiently high.

Next, a reproduction optical system that divides the reflected light from the magneto-optical recording medium 21 into two optical paths according to the angle of the polarization plane rotates the polarization plane of the reflected light beam from the magneto-optical medium 21 that has passed through the beam splitter 25. A polarizing beam splinter 28 divides the light into two optical paths with intensities according to the rotation angle of the polarization plane by a λ/2 plate 27, and a polarizing beam splitter 28 condenses the light transmitted through the polarizing beam splitter 28 and converts the light into an avalanche photodiode (hereinafter simply referred to as A condensing lens 29 that condenses light onto the APD (referred to as APD) 32
, the light reflected by the polarizing beam splitter 28 is
A condensing lens 30 that condenses light onto a photodiode (hereinafter simply referred to as PIN) 31 is provided. The multiplication factor of the APD 32 is set by the reverse bias voltage control circuit 35. The output of APD32 is input to current-voltage conversion amplifier 33, and the output of PIN31 is input to current-voltage conversion amplifier 3.
4 is input. The outputs of these amplifiers 33 and 34 are input to a differential amplifier 36, and a signal recorded on a medium from the output of the differential amplifier 36 is reproduced. In FIG. 2, numerals 31 to 36 are magneto-optical medium reproducing circuits.

(Problems to be Solved by the Invention) In the configuration of the conventional reproducing circuit as described above, two current-voltage conversion amplifiers 33 and 34 are essential, and various factors such as frequency characteristics and temperature characteristics of these amplifiers are required. It is an absolute condition for increasing the common mode rejection ratio (CMRR) of the differential amplifier 36 in the subsequent stage that the characteristics of However, it is very difficult to perfectly match the frequency characteristics, temperature characteristics, and other various characteristics of two amplifiers, so CMRR
In other words, there is a limit to the improvement in the S/N ratio of the reproduced signal.

Also, by manually adjusting the reverse bias voltage applied to the APD,
There is a problem in that it takes time to match the output converted by the PIN because the adjustment work is done while checking the output of the differential amplifier with a measuring device.

Furthermore, even if adjustments could be made perfectly at the manufacturing stage,
When the usage environment changes, for example, the optical system becomes dirty due to changes in temperature or aging, the CMRR naturally decreases.
There was a problem that the S/N ratio of the reproduced signal deteriorated.

The present invention solves these problems by creating a differential circuit consisting of one current-voltage conversion amplifier, relaxing the conditions for selecting the characteristics of the photoelectric conversion amplifier, and changing the levels of two input DC signals. By configuring a variable amplification circuit, such as an avalanche photodiode, to automatically control it so that it is always balanced, there is no need for any adjustment at the manufacturing stage (at the same time, there is no need for any adjustments due to environmental changes, aging, etc., such as dirt on the optical system). It is an object of the present invention to provide a magneto-optical medium reproducing device which can substantially completely remove the noise component of the reproduced signal without degrading the S/N ratio of the reproduced signal even when the reproduction signal is affected by the noise.

(Means for Solving the Problems) In order to solve the above problems, the inventors conducted extensive research and found that the main noise in magneto-optical media reproducing devices is caused by recording media of reflective type, that is, using the Kerr effect. If the medium uses transmission type light, that is, the Faraday effect, it is proportional to the average transmitted light intensity of the medium, and it is proportional to the intensity fluctuation of laser light that does not exhibit polarization characteristics. The present invention was completed by focusing on this point.

In the present invention, by directly calculating the difference between the input signal currents, a differential circuit can be constructed with one Ti current-voltage conversion amplifier without the need for two current-to-voltage conversion amplifiers, and the DC level of the two input signals can be adjusted. The gain control amplifier is controlled by combining an automatically balanced variable multiplication factor element or circuit, such as an avalanche photodiode or a photoelectric conversion element, with a gain control amplifier.

That is, the first photoelectric conversion means (PIN31
) and; a second photoelectric conversion means (APD32) with a variable amplification factor that photoelectrically converts the light from the other side of the optical path; and a control means (reverse bias voltage) that controls the amplification factor of the second photoelectric conversion means (APD32). a control circuit 35); separation means (capacitor C, CZ resistor R1) for separating the DC component and AC component contained in the respective outputs of the first and second photoelectric conversion means; a differential amplifier (12) that outputs a signal according to the difference between the two DC components separated by the separation means; a current-voltage conversion means (12) that converts the sum of the two AC components separated by the separation means into a current-voltage; a current-voltage conversion amplifier 11); the control means (35) controls the second voltage conversion amplifier so that the output of the differential amplifier becomes 0 according to the output of the differential amplifier (12);
The current-voltage conversion means (current-voltage conversion amplifier 11) is configured to control the multiplication factor of the photoelectric conversion means;
The structure is such that a reproduced output signal is obtained from the output of the .

(Function) Since the present invention is configured to directly calculate the difference in input signal current as described above, only one current-voltage conversion amplifier is required.
At the same time, the conditions for selecting the characteristics of the mamp can be greatly relaxed,
Since the DC levels of the two input signals are automatically balanced, it is possible to save the effort of adjustment at the manufacturing stage, and to prevent performance deterioration due to temperature changes during use or aging.

(Embodiment) FIG. 1 shows a circuit according to an embodiment of the present invention. Since the optical system is the same as that shown in FIG. 2, it will be omitted. Also, the same symbols as in Figure 2 represent the same effects.

In Figure 1, R+ and Rz are APD32 and P, respectively.
This is a resistor for separating and detecting the DC (low frequency) component in the output signal from IN31, and C1 and C2 are also resistors for detecting the DC (low frequency) component in the output signal from IN31.
This is a capacitor for separating and detecting high frequency components.

11 is a current-voltage conversion amplifier, and 12 is a differential amplifier.

The present embodiment shown in FIG.
1 and PIN31 are sequentially connected in series, the connection point between resistor R and resistor R2 is grounded, and the connection point between APD32 and resistor R1 is connected to one input terminal of differential amplifier 12 and one terminal of capacitor C1. connected to PIN31 and resistor R
2 is connected to the other input terminal of the differential amplifier 12 and one terminal of the capacitor C2, and the connection point with the capacitor C+
, Cl are both connected to the current-voltage conversion amplifier 11.
connected to the input terminal of The output of the differential amplifier 12 is connected to the reverse bias control circuit 3 of the avalanche photodiode 32.
The avalanche photodiode 32 is connected to the input terminal of the avalanche photodiode 32 to form a control loop, and the reverse bias of the avalanche photodiode 32 is controlled so that the output of the differential amplifier 12 becomes zero.

The reproduced output is obtained from the output terminal of the current-voltage conversion amplifier 11.

Here, when the reproduced information signal from the magneto-optical medium 21 is divided into two optical paths due to the difference in the plane of polarization, the reproduced information in both optical paths has a phase difference of 180° due to the rotation of the plane of polarization, while the noise component is Since it depends only on the strength of , it becomes an in-phase component. Therefore, information signals having a phase difference of 180' are obtained as a summed signal, and the in-phase noise components can be canceled out and removed by adjusting the multiplication factor of the APD to make their amplitudes the same. Here, since the information signal is a high frequency signal (alternating current signal), the high frequency signal current passes through capacitors C+ and Cz, and the in-phase components of the signal currents flowing through c, , and C2 are canceled out, and the difference between the signals whose phases are reversed is is input to the current-voltage conversion amplifier 11 and converted into a voltage.

The resistors R+ and Rz are for detecting DC components contained in the two input signals. Focusing on the fact that the DC component and the main noise component are in a proportional relationship and are in phase,
The multiplication factor of the APD 32 is adjusted by the reverse bias voltage control circuit 35 so that the DC components of the two signals are equal, and the in-phase noise component is removed. That is, since the differential amplifier 12 is configured to extract an output according to the difference between the DC components of two signals, the reverse bias voltage of the APD 32 is reverse biased so that the output of the differential amplifier 12 is zero. It is automatically controlled by the voltage control circuit 35.

In the above embodiment, A is used as a photoelectric conversion element with variable multiplication factor.
Although an example using a PD has been shown, the present invention is not limited thereto, and various elements and circuits may be used, such as a combination of a photoelectric conversion element and a gain control amplifier.

(Effects of the Invention) As explained above, according to the present invention, reproduced light due to reflection from a magneto-optical medium or i3 transmission is divided into two optical paths with different intensities depending on the angle of the polarization plane. Later, one of the reproduced lights is converted into an electrical signal by a pin photodiode (PIN), and the other reproduced light is converted into an electrical signal by an avalanche photodiode (APD) with an amplification function, and the difference between these currents is directly converted into an electric current. -Since the noise component of the signal is removed by voltage conversion, compared to the conventional method using two current-voltage conversion amplifiers and one differential amplifier, the current-voltage conversion amplifier does not use a differential amplifier. Since only one is required, the circuit can be simplified, and there is no noise due to differences in the characteristics of the current-voltage conversion amplifier. By simplifying the circuit, the wiring line length can be shortened, and the phase difference of the input signal can be reduced. can be kept small. With these, it is possible to reproduce an information signal with a high SZN ratio, and at the same time extract the DC component contained in each output obtained from the two photoelectric conversion means (PIN and API), and extract the DC component and the He discovered that the amplitudes of the main noise components are proportional and in phase, and by focusing on this point, he tried to make sure that the DC components were always equal.In other words, the noise components included in the differential amplification output signal were always the same. Since it is controlled to minimize the noise component that appears in the differential output even if the noise component fluctuates due to changes in the operating environment and usage conditions of the device over time, closed-loop control is performed that automatically minimizes the noise component that appears in the differential output. The magneto-optical reproducing device can always be kept in an optimal condition, the performance of the device can be maintained over a long period of time, and adjustment work during manufacturing can be made extremely simple.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a magneto-optical medium reproducing circuit according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram of a conventional magneto-optical medium reproducing apparatus. (Explanation of symbols of main parts) 31: PIN photodiode (PIN) 3
2 near balancier diode (APD) 33
．． 34.11: Current-voltage conversion amplifier 35: Reverse bias voltage control circuit 36.12; Differential amplifier Applicant: Nippon Kogaku Kogyo Co., Ltd. Agent Patent attorney: Takashi Watanabe Figure 1

Claims (1)

[Scope of Claims] A first photoelectric conversion means for photoelectrically converting light including polarization information from a magneto-optical medium on which information is recorded along one of two optical paths divided according to the polarization state; the optical path; a second photoelectric conversion means with a variable multiplication factor for photoelectrically converting the light emitted by the other one; a control means for controlling the multiplication factor of the second photoelectric conversion means; and each of the first and second photoelectric conversion means. Separation means that separates a DC component and an AC component contained in the output; A differential amplifier that outputs a signal corresponding to the difference between the two DC components separated by the separation means; current-voltage converting means for converting a difference between alternating current components into current-voltage; the first control means converts the second photoelectric conversion means so that the output of the differential amplifier becomes zero according to the output of the differential amplifier; A magneto-optical medium reproducing circuit, characterized in that the circuit is configured to control the multiplication factor of the current-to-voltage converter; and is configured to obtain a reproduction output signal from the output of the current-voltage conversion means.