JPS6371942A - Semiconductor laser driving circuit - Google Patents

Abstract

PURPOSE:To attain a driving circuit of a semiconductor laser having a flexibility by forming a reference voltage for setting the optical output of the semiconductor laser from a recording signal to make the high level and the low level of the optical output of the semiconductor constantly fixed without depending on the production probability of '1' and '0' of the recording signal. CONSTITUTION:An APC loop controls a bias current so as to make an optical output control signal 50 equal to an optical monitor signal 13 and consequently, the optical output of the semiconductor laser 1 is maintained to a constant value. If the response characteristic after the recording signal is inputted until the semiconductor laser emits light and the optical output monitor signal 13 is obtained is not equal to the responsiveness for obtaining a reference signal 12 is obtained from a reference voltage generating circuit 1, the APC is not normally operated. Then, the values of a resistance 44R3 and a capacitor 45C are suitably set and the characteristic of a low-pass filter is changed to set the above-mentioned responsiveness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical information recording/reproducing apparatus that uses a semiconductor laser as a source to perform recording, reproduction, or erasing.
This invention relates to a semiconductor laser drive circuit.

[Conventional technology]

In an optical information recording device using a semiconductor laser as a light source, a bias current supplied to the semiconductor laser is threshold-limited so that the optical output of the semiconductor laser is kept constant during information reproduction. AP0 below C: Automatic
During information recording, which is referred to as power control, it is common to perform pulse driving in such a manner that a recording signal is used to superimpose a pulse on a direct current bias of a semiconductor laser.

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.

It is converted into a voltage value by a resistor 21 and amplified by an amplifier 22 to obtain an optical output monitor signal 13. The low pass filter 23 is A
'The band of the PO loop is limited, and during recording, the recording signal band is cut so that the average value of the optical output of the semiconductor laser pulse-driven by the recording signal is monitored. During signal reproduction, the switch 2 is connected to the reproduction output reference voltage 25, and this voltage is compared with the optical output monitor signal 24 after passing through the low-pass filter by the differential amplifier 5.
Applied to the base of transistor 290. A current source is configured by the transistor 29 and the resistor 30, and supplies a bias current to the semiconductor laser 1. Control is performed so that the optical output of the semiconductor laser 1 is constant due to this loose PC.

Next, circuit operation during information recording will be explained.

A recording signal 11 is input from a terminal 10, and transistors 31 and 32 are alternately switched via a buffer 34 and an inverter 33. A constant current source is composed of the transistor 35, the resistor 36, the switch 37, and the voltage source 3B. During reproduction, the switch 37 is connected to GND, and during recording, it is connected to the pulse current setting reference voltage 58. When the recording signal is at a high level, the a-run raster 31 is turned on and the transistor 32 is turned off; when it is at a low level, the transistor 51 is turned off and the transistor 32 is turned on, and a pulse current is applied to the semiconductor laser 1. On the other hand switch 2
8 is connected to the recording output reference voltage E26 during recording, and monitor signal 2 monitors the average value of this voltage and optical output.
4 and 4 by a differential amplifier 5, and the bias current is controlled so that the average value of the optical output is constant.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology, 11" of the recording signal during recording.
If the probability of occurrence of ``0#'' and ``0#'' is not 1, the average value PM of the optical output changes as shown in FIG.
It deteriorates to H'. Such recording signals are, for example,
This occurs when attempting to record 2-7 modulation in NRZ (with bit corresponds to "1" and without bit corresponds to 10").

2-7 modulation is 0 between 11" and 11# of the data after modulation.
” can be from 2 to 7. Therefore, depending on the data pattern after modulation, even if the average value of the optical output does not change, the high level and D-level will change. Especially when the optical output Because bits are formed in the medium when the level is high,
If this varies, the size of the recorded bits will vary, causing problems such as increased jitter and increased error rate during signal reproduction, or in the worst case, bits may not be recorded.

SUMMARY OF THE INVENTION Therefore, the present invention is intended to solve these conventional problems, and its purpose is to provide a signal that can be recorded even when a modulation method is used in which the probability of occurrence of 11" and 0" in the recording signal is not equal to 1. Another object of the present invention is to provide a semiconductor laser drive circuit that controls the high level and low level of optical output so that they are always constant.

[Means for solving problems]

The semiconductor laser drive circuit of the present invention includes a pulse current drive circuit that applies a pulse current to the semiconductor laser according to a recording signal, and a process that converts and amplifies the current signal from the monitor photodiode that monitors the optical output of the semiconductor laser into a voltage value. ■#? during recording using the variable amplification circuit and the recording signal? a reference voltage generation circuit 1 that generates a voltage for setting the optical output of the conductive laser, a reference voltage generation circuit 2 that generates a voltage for setting the optical output of the semi-integrated laser during reproduction, and the reference voltage Calculate the output from the generator circuit 1.2 by g]170
a differential amplifier circuit that compares the output of the converter circuit with the output of the converter circuit; and a bias current that supplies a bias current to the semiconductor laser using the output from the differential amplifier circuit. It is characterized by consisting of a drive circuit.

[Effect]

According to the above configuration of the present invention, since the reference voltage for setting the optical output of the semiconductor laser is generated from the recording signal, the optical output of the semiconductor laser is APc is performed so that the high level and low level of the output are always constant.

〔Example〕

FIG. 1 is a block diagram of a semiconductor laser drive circuit of the present invention,
FIG. 4 is a specific circuit diagram of an embodiment of the invention. Components that are the same as those in FIG. 2 of the conventional example are indicated by the same numbers in the figure. A detailed explanation will be given below based on the drawings. The optical output of the semiconductor laser 1 is monitored by a monitor photodiode 2, and the obtained current signal is converted into a voltage by a resistor 21.
The optical output monitor signal 13 is amplified by the amplifier 1llIBi amplifier 22.
get. A portion 8 surrounded by thin dots in the middle of FIG. 4 is the reference voltage generation circuit 1. A recording signal 11 is input from a terminal 10. 42 is a TTL open collector type buffer (
74LSO7, etc.), and when the input is at a low level, the output is grounded to GND, and when the input is at a high level, the output is in an open state.

48 is a general operational amplifier. Set the value of resistor 42 to 81
, if the value of the resistor 43 is R1, when the input signal 11 is low level, the contact 49 is grounded to GND, so it becomes Ov, and when it is high level, the output of the buffer 41 is open, so the potential of the contact 49 is Ov. , the value obtained by dividing VCC by R, and B, that is, V CCX (a, + a, )
becomes. The value of the resistor 44 is R8, the value of the capacitor 45 is C1, the value of the resistor 46 is R3, and the value of the resistor 47 is Rs. A low pass filter is made up of a resistor 44 and a capacitor 45. Cutoff I+! 6 wave number/c becomes fc=-211.

The operational amplifier 48 and resistors 46 and 47 form a non-inverting amplification circuit. FIG. 5 shows the waveforms of each part.

A signal 12 in the figure is the output of the reference voltage generation circuit 1. Here, .

The switch 59 and the reference voltage 40 constitute the reference voltage generation circuit 2. The switch 39 is controlled to be connected to GND when the semiconductor laser is not emitting light, and connected to the reference voltage 40 when the semiconductor laser is emitting light for signal reproduction, recording, etc. Note that the switch 39 can be easily realized using a device such as an analog switch. Let V be the potential of the reference 'i4 voltage 40. An adder circuit 4 calculates vl and V by ha, and an optical output control signal 50 is obtained. As shown in FIG. 5, the recording signal 11 is at low level nVt, and when the recording signal is at high level it is V, +V.

On the other hand, the optical output monitor (No. 8 13 shows vH when the recording signal 11 is at high level and vL when it is at low level as shown in Fig. 5).
Assume that the waveform is as follows. The band is determined by the junction capacitance of the monitor photodiode 2 and the resistor 21, and is limited by the cut-off frequency or the response of the amplifier 22. Differential amplifier circuit 5
Find the difference between the optical monitor signal 15 and the optical output control signal 50,
applied to the base of transistor 290. transistor 2
9 and a resistor 50 constitute a bias current drive circuit, which supplies a bias current to the semiconductor laser 1. The APO loop described above controls the bias current so that the optical output control signal 50 and the optical monitor signal 15 are equal.
As a result, the optical output of the semiconductor laser 1 is maintained at a constant value.

Here, the response from when the recording signal 11 is input until the semiconductor laser emits light and the optical output monitor signal 13 is obtained is the same as the response from the reference voltage generation circuit 1 until the reference signal 12 is obtained. Without it, Apc will not work properly. Therefore, the values of the resistor 44R8 and the capacitor 45C are set appropriately, and the characteristics of the low-pass filter are changed to match the above-mentioned response.

〔Effect of the invention〕

As described above, according to the present invention, the following effects are brought about. Even if recording is performed using a modulation method in which the probability of occurrence of "1#" and "0' in the recording signal is not 1/2, such as 2-7 modulation, the reference signal for controlling the optical output of the semiconductor laser cannot be obtained from one recording signal. Therefore, a stable light output is always obtained.

Therefore, the jitter of the recorded bits is reduced, and the error rate of the reproduced signal is improved. Furthermore, as shown in FIG.
Regardless of whether you record using the NRZ-1 method (a method that inverts the recording signal at 11" of data) or with the NRZ-1 method (a method that inverts the recording signal at 11" of data), the reference signal 13 is created according to the recording signal, so There is no problem.For the above reasons, even if the recording signal modulation method changes from 2-7 modulation to MFM or another method such as 8t010 modulation, or the transfer speed of the recording signal changes, there will be no problem during recording. This is a flexible semiconductor laser drive circuit that performs APC.

[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 an X-P characteristic diagram of a semiconductor laser. FIG. 4 is a semiconductor laser drive circuit diagram in one embodiment of the present invention. FIG. 5 is a signal waveform diagram of each part of FIG. 4. FIG. 6 is a diagram of signal waveforms at various parts in both the NRZ and NRZ-1 systems. 1... Semiconductor laser 2... Monitor photodiode 3...
・・・・・・Engineering→V conversion amplifier circuit 4・・・・・・・・・I
70 arithmetic circuit 5...Differential amplifier circuit 6...Bias whisker flow drive circuit 7...
......Pulse current drive circuit 8...Reference voltage generation circuit 19...Reference uneven pressure generation circuit 2 Figure 2

Claims (1)

[Scope of Claims] a) A semiconductor laser drive circuit for an optical recording/reproducing device that performs recording, playback, or erasing using a semiconductor laser, and b) a pulse current drive circuit that applies a pulse current to the semiconductor laser in accordance with a recording signal; c) I→V, which 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; and d) a reference voltage generation circuit 1 that generates a voltage for setting the optical output of the semiconductor laser during recording based on the recording signal.
and e) a reference voltage generation circuit 2 that generates a voltage for setting the optical output of the semiconductor laser during reproduction, and f) the reference voltage generation circuit 1 and the reference voltage generation circuit 2.
g) a differential amplifier circuit that compares the output of the I→V conversion amplifier circuit with the output of the adder circuit; h) 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.