JPS63117333A - Semiconductor laser driving circuit - Google Patents

Abstract

PURPOSE:To perform accurate erasure without rounding the driving current of a semiconductor laser by providing an erasure current driving circuit which drives an erasure current by such a way that it is added to a bias current when the operation of the semiconductor laser is changed from a playback state to an erasure state or vice versa. CONSTITUTION:This circuit is equipped with a pulse current driving circuit 7 which applies a pulse current to the semiconductor laser with a recording signal, the erasure current driving circuit 7 which supplies a current to the semiconductor laser at the time of erasure, and an I-V converting amplifier circuit 3 which converts and amplifies a current signal from a monitor photodiode for monitoring the light output of the semiconductor laser to a voltage value. Further, this is equipped with an adding circuit 4 which adds the outputs of reference voltage generating circuits 1, 2, and 3, a differential amplifier circuit 5 which compares the output of the I-V converting amplifier circuit 3 with the output of the adding circuit 4, and a bias current driving circuit 6 which supplies the bias current to the semiconductor laser with the output of the differential amplifier circuit 5. The erasure current and bias current are added and applied by the erasure current driving circuit 7, so the transient response from the playback state to the erasure state is not rounded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser drive circuit for an optical recording/reproducing device that performs recording, reproduction, and erasing using a semiconductor laser.

[Conventional technology]

In an optical information recording/reproducing apparatus using a semiconductor laser as a light source, a bias current supplied to the semiconductor laser is controlled so that the optical output of the semiconductor laser is kept constant during information reproduction. (Hereinafter referred to as PC: Astomat
When recording information, it is common to pulse-drive a semiconductor laser using a recording signal in a manner that a pulse current is superimposed on a DC bias.

FIG. 2 is a conventional semiconductor laser drive circuit diagram.

The optical output of the semiconductor laser 1 is monitored by a monitor photodiode 2 and detected as a current signal.

A 1→V conversion amplification circuit composed of an operational amplifier 21 and a resistor 22 converts the signal into a direct voltage, and serves as an optical output monitor signal.

The low-pass filter 28 is connected to the band tj! of the APC loop. /, and at the time of recording, the recording signal band is cut so as to monitor the average directivity of the optical output of the semiconductor laser l pulse-driven by the recording signal. During signal reproduction, the switch 24 controls the reproduction output. It is connected to a reference voltage 25, and this voltage and the optical output monitor signal 24 are compared by the differential amplifier 5 and applied to the pace of the transistor 29 after passing through the % low-pass filter 2B.

The transistor 29 and the resistor 30 constitute a current source, which supplies a bias current to the semiconductor laser 1. Control is performed by this Arc loop so that the optical output of the semiconductor laser 1 is constant.

Next, circuit operation during information recording will be explained.

A recording signal 13 is input from a terminal 12, and transistors 31 and 32 are alternately switched via a buffer 34 and an outputter 33. A constant current source is configured by the transistor 35, the resistor 36, the switch 37, and the pulse current setting reference voltage 38.

The switch 37 operates by being connected to VCC during reproduction and to the pulse current setting reference voltage 38 during recording.

When record im No. 13 is level...transistor 3
1 is on, transistor 32 is off, and when the level is low, conversely, transistor 31 is off, transistor 3 is off.
2 is turned on, and a pulse current is applied to the half-four body laser l. On the other hand, the switch 24 is connected to a recording output reference voltage 26 during recording, and the differential amplifier 5 calculates the difference between this voltage and a monitor signal 25 that monitors the average directivity of the optical output.
The bias current is controlled so that the average light output is constant.

Further, during erasing, the switch 24 is connected to the erase output reference voltage 27, and the differential amplifier 5 compares the optical output monitor signal 24 with the erase output reference voltage 27 in the same way as during reproduction.
Perform the action.

[Problem that the invention seeks to solve]

However, in the prior art described above, when changing the operation of the semiconductor laser from the reproducing state to the erasing state or vice versa, the third
As shown in the figure, the current applied to the IC1 semiconductor laser has a rounded waveform due to band limitation by the low-pass filter 28. As a result, the problem arises that the first part of the area to be erased is left unerased, and the initial part that should not be erased is erased.

One object of the present invention is to solve these conventional problems, and its purpose is to provide a semiconductor laser drive circuit that can accurately erase only the region desired to be erased.

Means for Solving Problem c] The present invention provides a pulse current drive for applying a pulse current to the semiconductor laser according to a recording signal in a semiconductor laser drive circuit of an optical recording/reproducing device that performs recording, playback, and erasing using a semiconductor laser. circuit, an erase current drive circuit that supplies current to the semiconductor laser during erasing, an I→V conversion amplifier circuit that directly converts and amplifies the current signal from the monitor photodiode that monitors the optical output of the semiconductor laser to a voltage, and A reference voltage generation circuit 1 that generates a voltage for setting the optical output of a semiconductor laser; and a reference voltage generation circuit 2 that generates a voltage for setting the optical output of the semiconductor laser during recording based on the recording signal. and a reference voltage generation circuit 3 that generates a voltage for setting the optical output of the semiconductor laser during erasing.
an adder circuit that adds outputs from the reference voltage generation circuit 1, the reference voltage generation circuit 2, and the reference voltage generation circuit 3;

It consists of a differential amplifier circuit that compares the output of the ■→V conversion amplifier circuit and the output of the adder circuit, and a bias current drive circuit that supplies a bias current to the semiconductor laser using the output from the differential amplifier circuit. It is characterized by

[Effect]

According to the above configuration of the present invention, when erasing information, the erasing current drive circuit applies an erasing current plus a bias current to the semiconductor laser, so that the semiconductor laser has no dull transient response from the reproduction state to the erasing state. It becomes possible to drive.

[Implementation row]

FIG. 1 is a block diagram of a semiconductor laser drive circuit of the present invention,
FIG. 4 is a specific circuit diagram of one embodiment of the present invention. Components in the conventional column that are the same as those in FIG. 2 are designated by the same numbers in the figure. A detailed explanation will be given below based on the drawings.

A recording signal 13 is input to the terminal 12, an erase signal 15 is input to the terminal 14, and a read signal 17 is input to the terminal 16. The erase signal 15 becomes aHa during erasing,
Otherwise, it is "Ll". The read signal F is in the 'El state when the semiconductor laser emits light, and is in the "Ll" state when it does not emit light. Also, the recording signal 13 is on the recording medium. The digital signal corresponds to 111 for recorded pits and 101 for no pits.

A current signal obtained by monitoring the optical output of the semiconductor laser 1 with a monitor photodiode 2 is converted into a direct voltage f by an I→V conversion amplifier circuit composed of an operational amplifier 21 and a resistor 22. 39 is an inverting amplifier, which matches the polarity of the Al'C loose. The difference between the optical output monitor signal 18 and the reference voltage 40 is taken by the differential amplifier circuit 5. Low pass filter 28 is A
Limits the power of the PC loop. 11 is a reference voltage generation circuit 2, which includes a switch 53, an operational amplifier 54, and a resistor 51.
52 and a voltage source 50. The switch 53 is composed of an array of analog switches and the like, and is turned on when the erase signal 1 is 11i1. At that time operational amplifier 5
At the output of the buffer composed of 4, there are resistors 51 and 5.
The voltage divided by 2 can be obtained directly. The eraser determines the erase current to be added to the bias current during erase. An operational amplifier 59 adds the output of the aforementioned low-pass filter and the output of the reference voltage generation circuit 110. Resistor 30 and transistor 2
9 constitutes a current source, which also serves as erase current drive circuit 6 and erase current drive circuit 8 in FIG. The operation during signal reproduction is the same as that of the conventional array, so a detailed explanation will be omitted.

Next, the operation during signal recording will be explained.

The operation of the pulse current drive circuit 7 is the same as in the conventional column. A portion 10 surrounded by a dotted line in FIG. 4 is the reference voltage generation circuit 2. A recording signal 137:)E is input from the terminal 12. 41 is a τTL open collector type buffer (
For example, 74L807).

When the input is low level, the output is grounded to GND.

When high level is input, the output is in an open state.

48 is an operational amplifier. R1 is the direct line of resistor 42, resistor 4
3 is R2, the output of the buffer 41 is Ov when the input signal 13 is low level, and vc when the input signal 13 is high level.
The voltage is directly divided by the cf resistors 42 and 43, that is, "Icc*R2/(R1+R2)."

Next, the directivity 'f of the resistor 44, R3, and Il of the resistor 46! R
4. Let R5 be the value of the resistor 47, and flII of the capacitor 45 be C. A low pass filter is made up of a resistor 44 and a capacitor 45. This low-pass filter has the same characteristics as the low-pass produced by the monitor photodiode 2 and the 1→V conversion amplifier circuit, and has a cutoff frequency IPc.

A non-inverting amplifier circuit is made up of an operational amplifier 48 and resistors 46 and 47, where FC=1/(2πCR3), and its gain G is.

G=l+R5/R4 In FIG. 5, which shows the waveforms of each part, the signal 49 is the output of the reference voltage generation circuit 2. The recording signal 13 is m
H'* o Toki, signal 49UVl and nari.

Recording signal 13 is 'L'#, ()ND, II/tonal.

The adder circuit 4 is composed of an operational amplifier, etc., and the signal 4
9 and the voltage source (voltage is 72) 55 are added.

As a result, the output 40 of the adder circuit 4 becomes as shown in FIG.

This signal 40 is a reference voltage that determines the optical output of the semiconductor laser, and the difference between the signal 40 and the optical output monitor signal 18 is taken by the differential amplifier circuit 5 and is inputted to the bias current drive circuit through the low-pass filter 28. The pulse current drive circuit portion is the same as that described in the conventional column, so a description thereof will be omitted.

FIG. 6 shows the signal waveforms of each part, read signal 17, erase signal 14. When the recording signal 13 changes as shown in the figure, a reference voltage 40 is obtained.

FIG. 7 shows another embodiment of the erase current drive circuit portion of the present invention. This circuit is of a current addition type.

Voltage source 60, switch 61-resistance 63, transistor 6
An erase current drive circuit consisting of 4. drives a current to the semiconductor laser 1 in a form that is added to the bias current. here,
The switch 61 has the erase signal 1.5 set to 'IJ' (0 o'clock 1d'l c cK, 'H'ORF!' to the pressure 11!1).
60 and supplies current to the semiconductor laser 1 during erasing.

〔Effect of the invention〕

As described above, according to the present invention, when changing the operation of a single-handed conductor laser that brings about the following effects from the reproducing state to the erasing state or vice versa, erasing is performed by adding it to the bias current. Since we provided an erase current drive circuit to drive the current, the drive current of the semiconductor laser does not become dull, so the first part of the area to be erased is sometimes erased.

Territory that must not be erased! l! e There is no possibility of erasure, and the data can be erased accurately. Furthermore, since the present invention includes a bias current drive circuit, an erase current drive circuit, and a pulse current drive circuit, the optical output of the semiconductor laser during reproduction, recording, and erasing can be controlled independently.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a semiconductor laser drive circuit according to the present invention. FIG. 2 is a conventional semiconductor laser drive circuit diagram. FIG. 3 is a diagram of signal waveforms at each part. The fourth factor is a semiconductor laser drive circuit diagram of an embodiment of the urine invention. FIG. 5 is a signal waveform diagram of each part of the embodiment. FIG. 6 is a signal waveform diagram of each part of the implementation column. FIG. 7 is a circuit diagram of the main parts of another embodiment of the present invention. 1...Semiconductor laser 2...Monitor photodiode 3...L→V conversion amplifier circuit 4...Fist addition circuit 5...-Differential amplifier circuit 6...Bias current drive circuit 7...Erasing current Drive circuit 8...Pulse current drive circuit and more

Claims (1)

[Scope of Claims] a) A semiconductor laser drive circuit for an optical recording and reproducing device that performs recording, playback, and erasing using a semiconductor laser, and b) a pulse current drive circuit that applies a pulse current to the semiconductor laser in response to a recording signal; c) an erase current drive circuit that supplies current to the semiconductor laser during erasing, and d) an I→V circuit that converts and amplifies the current signal from the monitor photodiode that monitors the optical output of the semiconductor laser into a voltage value.
a conversion amplifier circuit; e) a reference voltage generation circuit 1 for generating a voltage for setting the optical output of the semiconductor laser during reproduction; and f) for setting the optical output of the semiconductor laser during recording using the recording signal. Reference voltage generation circuit 2 that generates a voltage of
and g) a reference voltage generation circuit 3 that generates a voltage for setting the optical output of the semiconductor laser during erasing; h) the reference voltage generation circuit 1, the reference voltage generation circuit 2, and the reference voltage an adder circuit that adds the outputs from the generator circuit 3; i) a differential amplifier circuit that takes the difference between the output of the I→V conversion amplifier circuit and the output of the adder circuit; and j) the output from the differential amplifier circuit. A semiconductor laser drive circuit comprising a bias current drive circuit that supplies a bias current to a semiconductor laser by its output.