JPH02195529A - Magneto-optical disk tester - Google Patents

Abstract

PURPOSE:To improve measuring accuracy for a bit error rate, etc., by controlling a sum signal and a difference signal which vary by the reflectance of a disk, the change of a laser emitting power and kerr rotational angle so that they have a certain amplitude. CONSTITUTION:By alternately switching the sum signal and the difference signal obtained by detecting the reflected light of a magneto-optical disk by two photodiodes, the information of a preformat part is read from the sum signal and the information of a data part is read from the difference signal. In such a case, based on a laser emitting power set value PR, a kerr rotational angle set value thetaK which are previously set, and an average reflectance RL in an area measuring the bit error rate, etc., a gain in proportion to the PR and the RL is set for a programable gain amplifier 3 for the sum signal and the gain in proportion to the PR, the thetaK and the RL is set for a programable gain amplifier 4 for the difference signal. Thus, the sum signal and the difference signal having a certain amplitude without receiving the effect of the reflectance of the magneto-optical disk 1, the emitting power of the laser light and the kerr rotational angle if bit pitch is fixed every disk 1.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a magneto-optical disk tester for testing the characteristics of a magneto-optical disk, and particularly relates to an improvement of an RF preamplifier section for amplifying RF flaw signals.

<Prior art> In a magneto-optical disk tester, the reflected light from the disk is detected by two photodiodes in a differential optical system.
It converts it into an electrical signal and extracts it. Track numbers and sector numbers on magneto-optical disks are recorded in the preformat section as changes in reflectance, so the sum of the outputs of two photodiodes (called a sum signal) is read as the intensity of light, and the data is Since the direction of the magnetic field is recorded in the data section, the direction of the magnetic field is read by the difference output (referred to as a difference signal) of the differential optical system using the Kerr effect.

The RF preamplifier section provides the sum signal and the difference signal to the binarization circuit, but the RF preamplifier section provides the above sum signal and difference signal to the binarization circuit.
It is necessary to electrically convert the flaw signal as a sum output and the signal obtained from the data section as a difference output, adjust the amplitude to an optimum value, and then switch as appropriate to provide the signal to the binarization circuit.

Note that the amplitude of the sum output changes depending on the reflectance of the disc, the output power of the laser beam, and the bit pitch, and the amplitude of the difference output changes depending on the Kerr rotation angle in addition to the above. be.

<Problems to be Solved by the Invention> By the way, when measuring various types of disks with a conventional magneto-optical disk tester, variable resistors are provided for the sum output and the difference output, respectively, and the amplitude is adjusted by manual setting. At present, the gain is either fixed or left unadjusted.

However, there are problems with the manual setting method using a variable resistor, which is complicated, and with the fixed gain method, there are limitations on the types of disks that can be measured and the output power of the laser beam. Even if both discs are of the same type, there is a problem in that variations in each disc and fluctuations in laser beam output power during measurement affect the measurement results.

An object of the present invention is to provide a magneto-optical disk tester that can automatically absorb amplitude changes due to factors such as (1), (2), and (2) above in an RF preamplifier section.

Means for Solving the Problem> In order to achieve such an object, the first invention of the present application provides a magneto-optical disk tester with a sum signal for amplifying the sum signal with a gain set from the outside. A programmable gain amplifier, a programmable gain amplifier for a difference signal that amplifies the difference signal with a gain set externally, a preset laser emission power setting value PR, a Kerr rotation angle setting value θ, a bit error rate, etc. Based on the average reflectance R4 in the measurement area, for the programmable gain amplifier for the sum signal, R
The present invention is characterized in that it is equipped with a computer system having a function of setting a gain proportional to Pn·θ,·R4 for the programmable gain amplifier for the difference signal.

Further, in a second invention of the present application, a magneto-optical disk tester includes: a low-pass filter that removes high frequency components from the sum signal; a sample holder that samples and holds the output of the low-pass filter; and a sample holder that samples and holds the output of the low-pass filter; a divider for the sum signal to divide by the output; a divider for the difference signal to divide the difference signal by the output of the sample holder; and a divider for the difference signal to divide the difference signal by the output of the sample holder; A programmable gain amplifier for a difference signal that amplifies the output, and a control signal for the sample holder so that it is in a hold state during a write operation, and that sample and hold is repeatedly performed at a predetermined period during a read operation. a sample-hold control circuit to generate a sample-and-hold control circuit; a function for supplying a set value related to a preset Kerr rotation angle to the programmable gain amplifier for the difference signal to control the gain; and a function to control the gain of the sample-hold control circuit; The present invention is characterized by comprising a computer system having a function of providing a signal.

Effect> In the first invention of the present application, the gain in the programmable gain amplifier is automatically controlled based on a value set in advance by a computer system. As a result, for each disk, as long as the pit pitch is constant, a sum signal and a difference signal of constant amplitude can be obtained that are not affected by the reflectance of the disk, the output power of the laser beam, and the Kerr rotation angle.

In the second invention of the present application, the sum signal is obtained by AGO from the divider, and the force difference signal is controlled to have a certain amplitude by the divider, and then the Kerr rotation angle is controlled by the divider. By using a programmable gain amplifier to correct and amplify changes in signal amplitude in response to changes in signal amplitude, as long as the pit pitch remains constant, a constant amplitude is achieved that is unaffected by disc reflectance, laser beam output power, and Kerr rotation angle. A sum signal and a difference signal can be obtained.

<Example> The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of main parts showing an embodiment of a magneto-optical disk tester according to the present invention. In FIG. 0, 1 is a magneto-optical disk and 2 is an optical head section. The optical head section 2 includes a condensing optical system that condenses laser light emitted from a laser light source and irradiates it onto the magneto-optical disk 1, and performs tracking control and focus control by receiving the reflected light reflected from the surface of the magneto-optical disk. It consists of a servo optical system that detects reflected light in order to perform the above operations, and a differential optical system that receives the reflected light reflected from one surface of the magneto-optical disk and obtains a sum signal and a difference signal.

3 is a programmable gain amplifier for a sum signal whose gain is controlled by an external signal and amplifies the sum signal. 4 is a programmable gain amplifier for difference signals whose gain is controlled by an external signal and which amplifies the difference signal.

5 is a switch that selectively selects a sum signal or a difference signal; 6 is a 2FI conversion circuit that converts the signal applied via switch 5 to 2Fi; 7 is a demodulation circuit that demodulates the output (modulation signal) of the binarization circuit 6. A demodulation circuit also has a function of generating a switching control signal for controlling switching of the switch 5, and a measuring section 8 receives the output of the demodulation circuit 7 and calculates a bit error rate (BER) and the like.

Reference numeral 9 denotes a tester control computer system, which controls the output power and Kerr rotation angle, and the gain control of the programmable gain amplifier.

Reference numeral 10 denotes a keyboard through which setting values for output power and Kerr rotation angle can be entered.

Reference numeral 15 denotes a laser power control system that controls the laser light power of the focusing optical system of the optical head section 2 based on a control signal from the computer system 9.

Reference numeral 11 converts the control signal from the computer system 9 into analog and supplies it to the laser power control system 15.

A reflectance measuring system 16 measures the reflectance from the output of the servo optical system of the optical head section 2. The measurement results are digitized by an analog-to-digital converter (hereinafter referred to as an AD converter) 12 and then input to the computer system 9.

13 is a DA converter which converts the gain setting value given to the programmable gain amplifier 3 from the computer system 9 into analog form.

14 is a DA converter which converts the gain setting value given to the programmable gain amplifier 4 from the computer system 9 into analog form.

The operation in such a configuration will be explained next.

FIG. 2 is a diagram showing the operation flow. First, enter the laser output power PR (mW) from the keyboard 10.
and the Kerr rotation angle θH (deg).

A laser beam is irradiated onto the disk surface from the optical head section 2,
In the reflectance measurement system 16 that receives the reflected light at that time, the average reflectance RL (
%).

Next, the computer system 9 sets a gain setting value (GS,
M) is determined by the following formula.

GStll i = “-P R′ R.

(However, α is a proportional coefficient.) This set value is converted into an analog by the DA converter 13 and given to the programmable gain amplifier 3.

The computer system 9 also provides a gain setting value (GI) I to be given to the programmable gain amplifier 4 of the difference signal system.
FF) is also obtained by the following equation, converted into analog by the DA converter 14, and then applied to the programmable gain amplifier 4.

GOIFF=β°PR·θk −R [ (where β is a proportional coefficient) The gain is automatically set as described above, and the sum signal and difference signal are each amplified by a predetermined gain. The amplified signal is appropriately selected by a switch 5 and given to a 2 tn conversion circuit 6 and a demodulation circuit 7.

The measurement system 8 measures the bit error rate and the like based on the signal demodulated by the demodulation circuit.

In addition, in the embodiment, the configuration is such that the sum signal and the difference signal are handled for a magneto-optical disk, but it is also possible to use a differential optical system as an optical system that detects only the strength of general light and handles only the sum signal. If so, it is of course possible to automatically set the gain for write-once optical discs as well.

The configuration shown in FIG. 1 has the following effects.

■In order to automatically obtain the gain setting value using the preset laser output power, Kerr rotation angle, and disk reflectance determined in advance, and to apply this setting value to each programmable gain amplifier, This eliminates the need for complicated gain setting operations using variable resistors and the like.

■Since the reflectance is measured for each measurement disk, variations in reflectance for each disk can be absorbed.

Therefore, the influence of variations in reflectance on measurement results such as bit error rate is eliminated.

■Compared to a gift that uses an automatic gain control circuit (AGC circuit), which is a conventional means of automatically controlling the gain,
According to the present invention, there is an advantage that automatic gain control can be realized with a relatively simple configuration.

FIG. 3 shows another embodiment of the present invention in FIG.
Parts equivalent to those in the figure are given the same reference numerals.

31 is a divider for the sum signal, and 32 is a divider for the difference signal. 33 is a low pass filter that removes high frequency components of the sum signal, and 34 is a sample hold that samples and holds the output of the low pass filter 33.

A sample/hold control circuit 35 generates a sample/hold control signal for controlling sampling and holding operations in the sample/hold 34 in response to a write/read status signal given from the computer system 9.

The operation in such a configuration is as follows.

As shown in the time chart of FIG. 4, when the write/read status signal given from the computer system 9 is read, the sample hold control circuit 35 outputs a sample signal at a constant cycle (for example, every 500 μs). Always outputs a hold signal when writing.

The divider 31 divides the sum signal by the output value of the sample holder 34. The output signal (F) is subjected to AGC and has a constant amplitude. On the other hand, the divider 32 divides the difference signal by the output value of the sample holder 34 and outputs a signal (G).5. Since the amplitude of this signal changes compared to the sum signal due to the change in the Kerr rotation angle, it is amplified by the programmable gain amplifier 4 in the next stage so that it has the same flI width as the sum signal (signal H).

In this way, it is possible to obtain a sum signal that is unaffected by variations in the reflectance of the disk or the output power of the laser beam, and a difference signal such that GiQ does not change depending on the Kerr rotation angle.

In this case as well, if the differential optical system is configured to detect only the general strength of light and handle only the sum signal, it is of course possible to automatically set the gain for write-once optical discs in the same way. be.

According to the configuration of FIG. 3 described above, the following effects are achieved.

■Reflectance and laser output power can be automatically adjusted using AGO means, while Kerr rotation angle can be adjusted automatically using AGC means and a programmable gain amplifier, eliminating the need for complicated gains using conventional variable resistors, etc. No setting work is required.

■By using AGC means, it is possible to absorb (correct) variations in reflectance for each disk, as well as variations in reflectance within a disk and changes in laser output power. There is no influence on measurement results such as bit error rate.

<Effects of the Invention> As explained in detail above, according to the present invention, the sum signal and difference signal, which vary depending on changes in disk reflectance and laser output power, and Kerr rotation angle, can be automatically controlled to a constant amplitude. This has the effect of improving the accuracy of measurements such as pin 1 to error rate, and simplifying the system operation to WJ.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of main parts showing one embodiment of a magneto-optical disk tester according to the present invention, FIG. 2 is an operational flow diagram, FIG. 3 is a block diagram of another embodiment of the present invention, and FIG. 4 is a block diagram of another embodiment of the present invention. 3 is a time chart for explaining the operation in the configuration. DESCRIPTION OF SYMBOLS 1... Magneto-optical disk, 2... Optical head unit, 3° 4... Programmable gain amplifier, 5... Switch, 6... Binarization circuit, 7... Demodulation circuit, 8...・・・
Measuring unit, 9... Computer system, 10... Keyboard, 1.1.14... DA converter, 12.14
...A I) converter, 15... laser power control system, 16... reflectance measurement system, 31.32... divider,
33...Low pass filter, 34...Sample holder, 35...Sample and hold control circuit. Figure Z

Claims (2)

[Claims] (1) Detect the reflected light from the magneto-optical disk with two photodiodes to obtain a sum signal and a difference signal, and alternately switch the sum signal and difference signal and guide them to a processing means,
In a magneto-optical disk tester configured to read the information of the preformat section from the sum signal and the information of the data section from the difference signal, a programmable sum signal for amplifying the sum signal with an externally set gain is used. A gain amplifier, a programmable gain amplifier for the difference signal that amplifies the difference signal with a gain set externally, and measurement of preset laser emission power setting value P_R, Kerr rotation angle setting value θ_K, bit error rate, etc. Based on the average reflectance R_L in the region, a gain proportional to P_R・R_L is set for the programmable gain amplifier for the sum signal, and a gain proportional to P_R.R_L is set for the programmable gain amplifier for the difference signal.
- A magneto-optical disk tester comprising a computer system having a function of setting a gain proportional to θ_K·R_L. (2) detecting the reflected light from the magneto-optical disk with two photodiodes to obtain a sum signal and a difference signal; alternately switching the sum signal and the difference signal and guiding them to a processing means;
A magneto-optical disk tester configured to read information in the preformat section from the sum signal and read information in the data section from the difference signal includes a low-pass filter for removing high frequency components from the sum signal, and an output of the low-pass filter. a sample holder that samples and holds the sum signal; a sum signal divider that divides the sum signal by the output of the sample holder; a difference signal divider that divides the difference signal by the output of the sample holder; a programmable gain amplifier for the difference signal that amplifies the output of the divider for the difference signal with a gain set externally; and a programmable gain amplifier for the difference signal that amplifies the output of the divider for the difference signal with a gain set externally; A sample-and-hold control circuit generates a control signal for repeating sample-and-hold in a periodic manner, and a sample-and-hold control circuit provides a set value related to a preset Kerr rotation angle to the programmable gain amplifier for the difference signal to control the gain. 1. A magneto-optical disk tester comprising: a computer system having a function of providing a write/read status signal to the sample and hold control circuit;