JPH08249701A - Optical signal detecting/amplifying device - Google Patents

Abstract

PURPOSE: To miniaturize a system and to save the power without separating an RF signal from a servo signal by performing gain control of a head amplifier circuit based on output from a monitor photodetector. CONSTITUTION: Setting range I1 of an input current Iin in reproducing and setting range I2 of the input current Iin in recording are set so that the setting ranges are not superposed on each other, and a mode switch position is provided between the setting ranges I1 , I2 . Thus, the matter that a C/N value is made higher at a reproducing time and the matter that a dynamic range is made wider at a recording time are compatible even under a low source voltage. Thus, since the RF signal and the servo signal are dealt with without separating them, the system constitution is miniaturized, and a power saving is performed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to recording / recording on an optical recording medium.
The present invention relates to an optical signal detection / amplification device that amplifies an output from a light receiving element that receives reflected light from the optical recording medium in reproduction, and is particularly suitable for use as a head amplifier of an optical pickup or the like.

[0002]

2. Description of the Related Art For example, an optical disk recording / reproducing apparatus irradiates a laser beam onto an optical disk from an optical pickup incorporated in the apparatus to record / reproduce information.

The optical pickup includes a laser element for emitting a laser beam to an optical disc, and a high frequency superimposing circuit for applying the laser element to a laser element according to a signal obtained by superimposing information and a carrier component supplied from the outside. A monitor light receiving element for monitoring the amount of reflected light from the optical disc, a light receiving element for detecting the reflected light from the optical disc, for example, eight light receiving elements, and a head amplifier circuit for amplifying the output of an electric signal from the eight light receiving elements. Have

Among them, the head amplifier circuit is shown in FIG.
As shown in (a) and (b), a negative voltage of -V is basically applied from the anode side of the light receiving element 10.

The output on the cathode side of the light receiving element 10 is supplied to the non-inverting terminal (+) of the amplifier 11 in FIG. 3 (a), for example. The output signal of the amplifier 11 is output from the terminal 12 and is also fed back to the inverting terminal (−) of the amplifier 11 via the capacitor C11 and the resistor R11. Similarly, a capacitor C1 is provided on the non-inverting terminal side of the amplifier 11.
2. One end of the resistor R12 is connected, and the other end is grounded.

In FIG. 3B, for example, the light receiving element 1
The output from the cathode side of 0 is amplified in two stages by the two amplifiers 13 and 14 connected in series. This amplified signal is output from the terminal 15.

The head amplifier circuit of FIG. 3A is set to a low gain so that the signals from the light receiving elements A to F are used as servo signals as a preamplifier built in the monolithic IC shown in FIG. 4, for example. On the other hand, FIG. 3 (b)
The head amplifier circuit is set to a high gain so that the weak signals from the light receiving elements I and J are used as RF signals in the preamplifier built in the monolithic IC shown in FIG. 4, for example.

[0008]

By the way, FIG. 3 (a)
The head amplifier circuits of (b) are amplifiers 11, 1 respectively.
Since the resistors placed outside 3, 14 are fixed,
The output gain is also fixed. If the output gain is high in the head amplifier circuit, the output R
The C / N ratio of the F signal also becomes high.

However, the larger the output, the more easily the output signal of the head amplifier circuit is saturated, which narrows the dynamic range of the servo circuit arranged in the subsequent stage. Satisfying such contradictory conditions becomes more severe as the power supply voltage is lower.

In addition to this, an optical disk recording / reproducing apparatus for recording / reproducing an optical disk for both recording and reproduction has both a high C / N ratio required for reproduction and a wide dynamic range for recording. Two circuit configurations are required to be satisfied.

Further, as one of the requests from the user, for example, in order to enable operation for a long time, it is necessary for the optical disk recording / reproducing apparatus to reduce the consumption voltage. In order to satisfy this, the power supply voltage to be used must be kept low. In order to make the two contradictory conditions compatible with each other even with the low power supply voltage, there is only a method of separately treating the system of the apparatus when handling the RF signal and the servo signal and individually providing the amplifier.

In such a system that separates and processes each signal, since an amplifier is used individually, the circuit configuration becomes large.

Therefore, the present invention has been made in view of the above-mentioned circumstances, and an optical signal detection / amplification device capable of satisfying the requirements for downsizing of the circuit configuration and power saving under a low power supply voltage. For the purpose of providing.

[0014]

In order to solve the above-mentioned problems, an optical signal detecting / amplifying device according to the present invention includes a monitor light receiving element for detecting the irradiation light amount applied to an optical recording medium,
A light receiving element for detecting reflected light from the optical recording medium, and a variable gain amplifying section for amplifying an output from the light receiving element,
It is characterized in that the gain control of the variable gain signal amplification section is performed based on the output from the monitor light receiving element.

[0015]

In the optical signal detecting / amplifying device according to the present invention, the gain control of the variable gain signal amplifying section is performed based on the output from the monitor element, so that, for example, the C signal of the RF signal can be reproduced at the low power supply voltage when reproducing the optical recording medium. Since the / N ratio is proportional to the square root of the gain, the gain can be increased, and since the RF signal is not read during recording, the dynamic range can be widened.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical signal detecting / amplifying device according to the present invention will be described below with reference to the drawings.

In this embodiment, an example in which the optical signal detecting / amplifying device of the present invention is applied to an optical pickup of a magneto-optical recording / reproducing device will be described.

This magneto-optical recording / reproducing apparatus irradiates the magneto-optical disk 1 with a laser beam and receives the reflected light from the surface of the magneto-optical disk 1, and according to a signal from the optical pickup 2. It has a signal processing unit 3 that performs servo signal processing.

The optical pickup 2 reflects a laser light emitting element 2a which operates according to information from the outside and a part of light emitted from the laser light emitting element 2a in the direction of the magneto-optical disk 1, and at the same time, the laser light emitting element. Mirror 2b that transmits a part of the light emitted from 2a, a monitor light-receiving element 2c that transmits the mirror 2b and monitors the light amount of the laser light-emitting element 2a, a magneto-optical disk 1 that reflects the light, and a mirror 2b that transmits the light. A light receiving section 2d that detects light including both RF / servo components, a monitor amplifier circuit 2e that amplifies the output from the monitor light receiving element 2c, and a threshold that is a threshold value for which the output from this monitor amplifier circuit 2e is set. Comparison control circuit 2f that discriminates levels according to level and outputs a control signal
And a head amplifier circuit 2g whose gain is controlled according to the output from the comparison control circuit 2f.

The laser light applied to the magneto-optical disk 1 is condensed by the objective lens 2h.

The light-receiving portion 2d uses a total of eight light-receiving elements, six in order to detect a servo signal, in addition to two provided in order to obtain information from the magneto-optical disk 1 as an RF signal. The RF signal and the servo signal are detected with a smaller number of elements than the above.

The monitor amplifier circuit 2e supplies an output to the auto power control circuit 3a which controls the light quantity of the laser beam in the signal processing section 3 of the apparatus body. The monitor amplifier circuit 2e feeds back a signal to the input terminal via the resistor R1.

Similarly to the monitor amplifier circuit 2e, the head amplifier circuit 2g also feeds back the output through the variable resistor VR. The variable resistor VR controls the gain switching of the head amplifier circuit 2g by switching the resistance value according to the output from the comparison control circuit 2f. The head amplifier circuit 2g outputs the output to the signal processing unit 3 of the apparatus body as an RF signal / servo signal.

The auto power control circuit 3a of the signal processing unit 3 feeds back the output to the laser light emitting element 2a as a control signal so as to keep the quantity of light irradiated at each recording constant.

The monitor amplifier circuit 2e supplies the output to the comparison control circuit 2f. The comparison control circuit 2f performs level discrimination by comparing with the threshold level,
It is supplied to the variable resistor VR of the head amplifier circuit 2g as a selection signal used for gain switching control of the head amplifier circuit 2g. Here, the comparison control circuit 2f also performs level shift at the same time in order to match the shift of the variable resistor VR of the head amplifier circuit 2g with an appropriate operation level. The comparison control circuit 2f supplies a low selection signal for a certain threshold level during reproduction and a high selection signal for a certain threshold level during recording. By supplying this selection signal, the head amplifier circuit 2g performs automatic gain switching control. This gain will be described in detail later.

As the optical signal detecting / amplifying device, the light receiving portion 2d, the monitor amplifier circuit 2e, and the comparison control circuit 2 are provided on one chip.
f and the head amplifier 2g are mounted in one IC. This optical signal detection / amplification device can be downsized as compared with the conventional configuration, and thus the optical pickup can be downsized.

When reproducing information from the magneto-optical disk 1, the amount of light emitted from the laser light emitting element 2a is small. Therefore, the input current I _in to the head amplifier circuit 2g is small. Therefore, when the variable resistor VR is switch-controlled to increase the resistance value, the voltage of the output signal becomes large. Here, when the value of the gain resistance of the variable resistor VR is R, the voltage V _{OUT of the} output signal of the head amplifier circuit 2g is expressed as V _OUT = R · I _in (1).

On the other hand, thermal noise V generated by the resistance V
_Noise is expressed as V _noise = √ (4k · T · R) (2), where Boltzmann constant is k and temperature is T. The C / N ratio is the thermal noise V generated by the resistance.
_{Since it} is expressed as the ratio of the voltage V _OUT of the output signal to _noise , C / N = V _out / V _noise = I _in · √R / (2√ (k · T)) ∝√R (3) Becomes As is clear from equation (3), the C / N of the RF signal
It can be seen that the ratio is proportional to the square root of the resistance value R of the variable resistor VR. As a result, during reproduction, the C / N ratio of the RF signal can be increased in proportion to the square root of the resistance value R.

Next, at the time of recording, the irradiation light amount from the laser light emitting element 2a is as large as about 10 times the irradiation light amount at the time of reproduction. That is, the input current I _in supplied from the light receiving section 2d to the head amplifier circuit 2g in accordance with the reflected light from the magneto-optical disk 1 increases. In consideration of this, the head amplifier circuit 2g is set to reduce the gain resistance value R of the variable resistor VR.

Since the RF signal is not read during this recording, it is not necessary to consider the C / N ratio which is one of the conditions.

Here, looking at the dynamic range of the output signal voltage V _out and the input current I _in , the output signal voltage V _out
The dynamic range of _out is, for example, as shown in FIG. 2, a range from the reference voltage V _ref to the maximum output voltage V _max .

In this embodiment, it is assumed that the reference voltage V _ref is 0, for example. The dynamic range of the input current corresponding to the dynamic range of the voltage of the output signal is, for example, as shown in FIG. 2, between the input current I _in = 0 and the maximum input current I _max , and the maximum input current I _max is When the resistance value R of the variable resistor VR is used, it is expressed by the relationship of I _max = V _max / R. Therefore, the dynamic range of the input current I _{in is} the dynamic range of the input current ∝1 / R ... ( It turns out that there is a relationship of 4). In the dynamic range of the input current I _in to the head amplifier circuit 2g, the voltage V _{out of the} output signal changes in the non-saturated state, as shown in FIG. The maximum output voltage V _max depends on the magnitude of the power supply voltage.

As described above, the dynamic range of the input current I _in is proportional to 1 / R. Further, since the dynamic range of the servo signal is inversely proportional to the gain, in order to increase the dynamic range of the servo signal, it is preferable to set the resistance value R of the variable resistor VR during recording to a low value. It will be.

In this way, by switching the gains according to reproduction and recording, compensation for increasing the C / N ratio and enlarging the dynamic range is performed. Actually, for example, as shown in FIG. 2, the set range I ₁ of the input current I _{in in} the play and the input current I _in the record (rec) are set.
set so as not to overlap the set range to each other and the setting range I ₂ of _in, are set switching position of the mode between the set range I _1, I _2.

Since the C / N ratio can be increased, R
The F signal can be expanded in band. This allows
By using the optical pickup configured as described above, it is possible to effectively operate even a magneto-optical recording / reproducing apparatus that requires high-density and high-speed operation. The band expansion of this RF signal is
The frequency characteristics near the carrier signal band become flat,
It is also effective in shifting a waveform distortion portion such as ringing that appears as unnecessary frequency characteristic variation to the high frequency side. It is possible to improve frequency characteristics near the carrier signal band.

With this configuration, it is possible to achieve both a high C / N ratio during reproduction and a wide dynamic range during recording, even if the power supply voltage is low. By satisfying this trade-off, RF
Since the signal and the servo signal can be handled without being separated, the system configuration can be further downsized.

In this embodiment, the magneto-optical disk is used as the applicable optical recording medium, but the present invention is not limited to the recording / reproducing medium or the package which requires a wide dynamic range, and is not limited to C / C.
Even if it is applied as a device for detecting an optical signal such as an information communication medium having a high N ratio, it can be operated in the same manner, which is effective.

With the above-described structure, it is possible to achieve both a high C / N ratio during reproduction and a wide dynamic range during recording, even with a low power supply voltage, and an RF signal. Since the servo signals can be handled without being separated, the system configuration can be further downsized and power consumption can be saved.

[0039]

According to the optical signal detecting / amplifying device of the present invention,
A high C / N ratio at the time of reproduction and a wide dynamic range at the time of recording can be compatible even with a low power supply voltage, and the RF signal and the servo signal can be handled without being separated. It is possible to further reduce the system configuration and save power.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment in which an optical signal detection / amplification device according to the present invention is applied to an optical pickup of a magneto-optical recording / reproducing device.

FIG. 2 is a diagram showing a relationship between an input current and an output voltage in a head amplifier of the optical pickup.

FIG. 3 is a diagram illustrating a circuit configuration of a conventional light receiving element and a head amplifier.

FIG. 4 is a diagram showing a configuration of a monolithic IC incorporating eight light receiving elements and a head amplifier using the above circuit configuration.

[Explanation of symbols]

 1 Magneto-optical disk 2 Optical pickup 3 Signal processing unit 2a Laser light emitting element 2b Mirror 2c Monitor light receiving element 2d Light receiving section 2e Monitor amplifier circuit 2f Comparison control circuit 2g Head amplifier circuit 2h Objective lens VR variable resistor R1 resistor

Claims (3)

[Claims] 1. A monitor means for detecting an irradiation light amount applied to an optical recording medium, a light receiving means for detecting a reflected light from the optical recording medium, and a variable gain amplifying means for amplifying an output from the light receiving means. An optical signal detecting / amplifying device comprising: a variable gain amplifying means based on an output from the monitor means. 2. The optical signal detecting / amplifying device according to claim 1, wherein the variable gain amplifying means is controlled so that the gain decreases during recording and the gain increases during reproducing. 3. The optical signal detecting / amplifying apparatus according to claim 1, wherein the output signal from said monitor means is discriminated by a predetermined threshold value to control switching of the gain of said variable gain amplifying means.