JPS63299583A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain the good signal of C/N by correcting the the amplitude difference of an output signal caused by the sensitivity difference of two photodetectors with the aid of a variable resistor connected between the mutual ground side terminals of two active elements and sufficiently extracting the reduction efficiency of in-phase noise caused by differential amplitude. CONSTITUTION:The output signals of the two photodetecting means 13 and 14 are inputted to a differential amplifier 15, the variable resistor Rv is inserted between the ground side terminals of the two active elements Tr1 and Tr2 of the differential amplifier 15, that means, between the emitters when the active elements Tr1 and Tr2 are bipolar transistors and the sensitivity difference of the two photodetecting means is corrected by adjusting the balance of the current of the ground side terminals of the two active elements Tr1 and Tr2, that means, the current of the emitters with the aid of the variable resistor Rv. Thus the in-phase noise of the output signal of the differential amplifier 15 is eliminated and the good signal of C/N can be obtained.

Description

Detailed Description of the Invention "Industrial Application Field" This invention is an optical recording and reproducing method in which a light beam emitted from a laser oscillator is irradiated onto an optical reproducing medium (two times) and an information signal contained in the reflected light or transmitted light is read out. Regarding equipment.

"Prior Art" Conventionally, in this type of optical recording and reproducing apparatus, a differential method has been used as a method for reproducing signals recorded on an optical recording medium. This method is known to remove common mode noise such as birefringence of the polycarbonate substrate and to obtain a signal with a high C/N ratio. However, if an amplitude difference occurs between the two input signals of the upstream differential amplifier due to variations in the photodetector, the common-mode noise removal effect is reduced. To solve this problem, conventional methods have been to attenuate the large-amplitude signal of the human input signal of the differential amplifier to match the amplitude of the small-amplitude signal, or to use an APD (avalanche) that can vary the amplification factor of the photodetector. The multiplication factor of one side was adjusted using a photodiode (photodiode).

``Problems to be Solved by the Invention'' In the conventional optical recording/reproducing device described above, in order to eliminate the difference in sensitivity between the two photodetectors (the difference in amplitude of the output signal due to the two), the output amplitude of the larger one is attenuated. The output amplitude is adjusted to the smaller output amplitude, or an APD is used as a photodetector, and the multiplication factor of one APD is changed.

The former method attenuates the output amplitude and therefore attenuates the carrier, which is disadvantageous for high C/N reproduction.

The latter has the disadvantage that stable performance over a long period of time cannot be obtained because the multiplication factor of the APD varies greatly in response to changes in reverse bias voltage.

[Means for Solving the Problems] In the optical recording/reproducing apparatus of the present invention, the output signals of the two photodetecting means are input to a differential amplifier, and the output signals are input between the ground terminals of the two active elements of the differential amplifier. In other words, if the active element is a bipolar transistor, between the emitters (the active element is a FET)
A variable resistor is inserted between the sources (in the case of a Correct the difference in sensitivity of the detection means.

"Embodiment" Next, an embodiment of the present invention will be described with reference to the drawings. 1st
The figure is a block diagram of an embodiment of the present invention, and is an example in which the present invention is applied to a magneto-optical disk device. In FIG. 1, a laser diode drive circuit 1 drives a laser diode 2. In FIG. The laser beam output from the laser diode 2 passes through a collimator lens 3, a beam shaping prism 4, a beam splitter 5 as a light distribution means, and an aperture lens 6, and reaches a magneto-optical disk 7. The light reflected by the magneto-optical disk 7 is split by the beam splitter 5 into transmitted light and reflected light. The distributed reflected light passes through a λ/2 plate 9 and is divided into transmitted light and reflected light by a polarizing beam splitter 10 serving as information signal distribution means.

The distributed transmitted light and reflected light are each transmitted through the aperture lens 1.
1.12, the light is received by PIN photodiodes 13.14 as photodetecting means, photoelectrically converted, and input to a differential amplifier 15. The magneto-optical disk 7 is connected to the spindle 1
6 and rotated by a spindle motor 17. The magnetic field generator 8 generates a magnetic field necessary for writing.

In FIG. 2, the load resistors RLI and Rb2 of the PIN photodiodes 13 and 14 and the load resistor Rc+*RC2 of the differential amplifier 15 have equal resistance values.

Also, the transistor T as an active element of the differential amplifier 15
, 1 and T, 2 are formed in the same puff cage,
have equal properties. A variable resistor Rv is connected between the ground terminals of the transistors T, 1 and Tr2, that is, between the emitters, and the emitter currents of the transistors T, 1 and Tr2 can be adjusted.

The polarization plane of the light distributed by the beam splitter 5 is rotated by passing through the λ/2 plate 9, and the polarization beam splitter 10 equally distributes the light amount on the passing side and the reflected side≦2, and the signal components are in opposite phases to each other. Become.

Therefore, the same amount of light enters the PIN photodiodes 13 and 141:. However, transistors Tr1 and Tr2
An amplitude difference occurs in the input signal (2) due to the sensitivity difference C2 between the PIN photodiodes 13 and 14. If ordinary differential amplification is performed in this state, the common mode noise removal effect will be incomplete. By connecting a variable resistor RV between the emitters and adjusting the balance of emitter currents of transistors Tr1 and Tr2, the common mode noise of the output signal of the differential amplifier 15 is sufficiently removed, and a signal with good C/H can be obtained. .

"Effects of the Invention" As explained above, this invention corrects the difference in output signal amplitude due to the difference in sensitivity between two photodetectors (from 2), it is possible to sufficiently bring out the common mode noise reduction effect due to differential amplification ≦ 2, /N
This has the effect of obtaining a good signal.

In this example, a transistor differential amplifier was used, but F
A similar effect can be obtained with an ET differential amplifier. Further, in the above description, the information signal is read from the light reflected from the magneto-optical disk 7, but the present invention is also applicable to the case where the information signal is read from the light transmitted from the magneto-optical disk 7.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of the differential amplifier shown in FIG. Patent applicant: NEC Corporation Representative Takashi Kusano 2
figure

Claims (1)

[Claims] (1) In an optical reproducing device that irradiates a light beam emitted from a laser oscillator onto an optical reproducing medium and reads out an information signal contained in the reflected light or transmitted light, the optical reproducing device is arranged in the optical path of the reflected light or transmitted light. A light distribution means, an information signal light distribution means disposed in one of the optical paths distributed by the light distribution means, and a light detection means disposed in each of the two light paths distributed by the information signal light distribution means. a differential amplifier into which the output signal of the photodetecting means is input; and a variable resistor connected between the ground side terminals of two active elements of the differential amplifier; An optical recording and reproducing apparatus, characterized in that the difference in sensitivity of the light detecting means is corrected by: