JPH08255367A - Optical signal detecting and amplifying device - Google Patents

Abstract

PURPOSE: To make compatible miniaturization with power saving of circuit constitution under a low source voltage by providing a monitor photodetector, etc., and controlling an output driving current with an amplifier part based on the output from the monitor photodetector. CONSTITUTION: This device is provided with the monitor photodetector 2c detecting an irradiation light quantity irradiating a magneto-optical disk 1 and a light receiving part 2d detecting reflected light from the magneto-optical disk 1. Further, the device is provided with a head amplifier circuit 2g amplifying the output from the light receiving part 2d and whose output driving current is controlled based on the output from the monitor photodetector 2c, and further, is provided with a monitor amplifier circuit 2e amplifying the output from the monitor light receiving element 2c, a comparison control circuit 2f comparing the output from the monitor amplifier circuit 2e with a set threshold level and shifting the level according to comparison, a signal processing part 3 performing servo processing according to a signal from an optical pickup 2 and an APC circuit 3a feeding its output back to a laser emitting element 2a as a control signal so as to hold the irradiation light quantity to a fixed level at a recording time.

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 users, for example, in order to enable operation for a long time, it is necessary for an 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,
It is characterized by having a light receiving element for detecting the reflected light from the optical recording medium, and an amplifying section for amplifying the output from the light receiving element and controlling the output drive current based on the output from the monitor light receiving element. .

[0015]

In the optical signal detecting / amplifying device according to the present invention, the amplifying section controls the switching of the output drive current amount based on the output from the monitor light receiving element, so that, for example, the RF signal is reproduced at the time of reproducing the optical recording medium at a low power supply voltage. Since the C / N ratio of is proportional to the square root of the gain, the gain is increased and R
Since the F signal is not read, 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 element 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 this monitor amplifier circuit 2e.
Comparison control circuit 2 that compares the output from the device with a set threshold level and shifts the level according to the comparison
f and a head amplifier circuit 2g whose output drive current amount is controlled based on the output from the light receiving section 2d based on the output from the comparison control circuit 2f.

The circuit inside the optical pickup 2 is made of Si.
In a so-called on-chip structure, for example, a photodiode is formed on a semiconductor substrate made of, for example, a light receiving element that detects an optical signal or a position corresponding to a light receiving section, and a bipolar transistor is formed in an amplifier section. One I
It is formed in C.

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

The light receiving section 2d uses a total of eight light receiving elements, six for detecting servo signals, in addition to two provided for obtaining 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 automatic power control circuit 3a which controls the light quantity of the laser light in the signal processing section 3 of the apparatus main body. The monitor amplifier circuit 2e feeds back a signal to the input terminal via the resistor R1.

The head amplifier circuit 2g is a differential amplifier circuit 2
g ₁ , a power amplifier circuit 2 g _2, and a current supply circuit 2 g ₃ whose output drive current amount is controlled according to the output from the comparison control circuit 2 f.

Similarly to the monitor amplifier circuit 2e, the head amplifier circuit 2g feeds back the output to the one input terminal side to which the input current I _in is supplied from the light receiving portion 2d via the resistor R2. The reference voltage V _ref is applied to the other input terminal of the head amplifier circuit 2g.

The head amplifier circuit 2g has a structure in which a differential amplifier 21 and an output power amplifier 22 are connected in series. Further, the power supply unit 22 is supplied from the current supply unit 23 with an output drive current I _drv which becomes an output current according to a control signal from the comparison control circuit 2 f. The current supply unit 23 supplies a large amount of the output drive current I _drv to the power amplification unit 22 during recording rather than during reproduction under the control of the comparison control circuit 2f. Therefore, the head amplifier circuit 2g uses the output as an RF signal / servo signal according to the output from the monitor amplifier circuit 2e, and the signal processing unit 3 of the apparatus main body.
Is output to.

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 amount of light emitted at each recording constant.

The monitor amplifier circuit 2e supplies the output to the comparison control circuit 2f. The comparison control circuit 2f outputs a signal corresponding to the comparison with respect to the threshold level as a selection signal used for switching control of the output drive current of the head amplifier circuit 2g, and outputs the output of the current supply circuit 2g of the head amplifier circuit 2g.
Supply to ₃ . By the supply of the selection signal, the current supply circuit 2g ₃ of the head amplifier circuit 2g supplies a selection signal of a low level with respect to a certain threshold level during reproduction, and a selection signal of a high level with respect to a certain threshold level during recording. Output current is automatically switched. The switching control of the output drive current amount will be described 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, the head amplifier circuit 2g has a large output when the resistance value of the resistor R2 is set to a high value. here,
If the gain resistance value of the resistor is R, the head amplifier circuit 2g
The output signal voltage V _OUT is expressed as V _OUT = R · I _in (1)

On the other hand, thermal noise V caused 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 gain resistance value R. As a result, C is proportional to the square root of the gain resistance value R during reproduction.
The / N ratio can be increased.

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, a current obtained by adding the output drive current I _drv from the current supply circuit 2g ₃ of the head amplifier circuit 2g is output.

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 _max2 .

For example, as shown in FIG. 2, the dynamic range is from the reference voltage V _ref to the first maximum output voltage V
_It is divided into two regions, up to _{max1 and} from the first maximum output voltage V _max1 to the second maximum output voltage V _max2 . The saturation level of the output voltage is set to V _max2 . Output voltage setting range I ₁ during playback and output voltage setting range I ₂ during recording
Are set in areas that do not overlap. If the gain resistance value R is used, the maximum input current I _max is I _max = V
_Since it is expressed by the relationship of _max2 / R, the input current I _in
It can be seen that the dynamic range of is related to the dynamic range of the input current ∝1 / R (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 output voltage V with respect to the dynamic range of the input current I _in is V in this embodiment when the reference voltage V _ref is 0, for example.
_max = (V _max1 + V _max2 ) = (V _max1 + F (I _drv ) ・
R). Moreover, since the dynamic range of the servo signal is in proportion to the output drive current I _drv , as a result, the dynamic range of the input current I _in is ∝F (I _drv ) ... (5) Is obtained. Therefore, in order to increase the dynamic range of the servo signal, it is preferable to increase the output drive current I _drv during recording.

In this way, by switching the gain in accordance with reproduction and recording, compensation for increasing the C / N ratio and increasing the range of the dynamic range is performed.

In practice, for example, as shown in FIG. 2, the setting range I ₁ of the input current I _{in in} the play and the setting range I ₂ of the input current I _{in in} the recording (rec) do not overlap with each other. To the setting range I ₁ ,
The mode switching position is set during 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 structure, 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 it is not limited to the recording / reproducing medium or the package which needs a wide dynamic range, and is not limited to 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 configuration, it is possible to achieve both a high C / N ratio at the time of reproduction and a wide dynamic range at the time of recording, even with a low power supply voltage. It is possible to reduce the size and power consumption.

[0043]

According to the optical signal detecting / amplifying device of the present invention,
Since 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, it is necessary to further reduce the system configuration and save power. You can

[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 section 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 21 Differential amplification section 22 Power amplification section 23 Current supply section 2h Objective lens R1, R2 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 reflected light from the optical recording medium, and an output driving current for amplifying an output from the light receiving means. An optical signal detecting / amplifying device, comprising: an amplifying means controlled based on an output from the monitor means. 2. The optical signal detecting and amplifying apparatus according to claim 1, wherein the amplifying means outputs an output drive current during recording which is larger than an output drive current during reproduction. 3. The optical signal detecting / amplifying device according to claim 1, wherein the non-saturated region is controlled by controlling the output drive current of the variable gain signal amplifying means.