JPS6364382A - Drive circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To control an optical output stably at all times, and to improve the error rate of a regenerative signal by monitoring the mean value of the optical output by a sample-holding circuit without depending upon a recording signal pattern. CONSTITUTION:A pulse-current drive circuit 7 applies pulse currents to a semiconductor laser 1 by a recording signal. AnI-V conversion amplifier circuit 3 converts and amplifies a current signal from a monitor photodiode 2 monitoring an optical output from the laser 1 to a voltage value. A sample timing generating circuit 8 generates timing when an output from the circuit 3 is sampled or held by the recording signal. A sample-holding circuit 4 samples or holds the output from the circuit 3 by a signal from the circuit 8. A differential amplifier circuit 5 compares an output from the circuit 4 and reference voltage. A bias-current drive circuit 6 supplies the laser 1 with bias currents by an output from the circuit 5. Accordingly, the optical output is controlled stably at all times, thus improving the error rate of a regenerative signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a semiconductor laser drive circuit for an optical information recording/reproducing apparatus that performs recording and reproduction using a semiconductor laser as a light source.

[Conventional technology]

In an optical information recording/reproducing device using a semiconductor laser as a light source, the bias current supplied to the semiconductor laser is controlled so that the optical output remains constant during information reproduction (hereinafter referred to as A p a : hwtomtxticPo).
control). Also, at the time of recording, J, + lever C case ≦, % crawling 1 no → Ishibinji fit 77
Pulse driving in a manner that superimposes 1r pulses is common.

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. Since the detection signal from the monitor photodiode is obtained 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. It determines the band of the low-pass filter APC loop, and during recording, the recording signal band is cut so as to monitor the average value of the optical output of the nine semiconductor lasers that are pulse-driven by the recording signal. First, during reproduction, the switch 28 is connected to the reproduction output voltage 25, and the difference between this voltage and the optical output monitor signal 24 that has passed through the low-pass filter 23 is taken by the differential amplifier 5, and is applied to the pace of the transistor 29. Ru. A current source is constituted by the transistor 29 and the resistor 30, and supplies a bias current to the semiconductor laser 1. Note that the APO loop is subjected to negative feedback b'-, and control is performed so that the optical output of the semiconductor laser 1 is constant.

Next, the operation during information recording will be explained. Recording signal 11 is input from terminal 10, and buffer 34 to inverter 3
3, transistors 31 and 32h are alternately switched. The transistor 35 and the resistor 36 constitute a constant current source. Switch 37#- is set to GNDI during playback.
C. During recording, it is connected to the pulse current setting reference voltage 68. When the recording signal 11 is at a high level, the transistor 31 is turned on and the transistor 32 is turned off, and when it is at a low level, the transistor 31 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, during recording, the switch 28 is connected to the recording output base voltage 26, and this voltage and the monitor signal 24 that monitors the average value of the optical output are mixed by the differential amplifier 5, so that the average value of the optical output is constant. The bias current is controlled so that

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology, "11" of the recording signal at the time of recording is
If the probability of occurrence of "0" is not A, as shown in Figure 3, the average value PM of the optical output does not change, but the low level pL and the high level pHh change to the heel. For example, such a recording signal may be 2-7 modulated with NRZ
(With pits corresponds to "11," without pits corresponds to "θ')
Occurs when trying to record. In the case of 2-7 modulation, the number of "0's" between #11 and "11" can be from 2 to 7. For example, when the pattern "1001" continues, the recording signal will be 11 and the monitor signal will be 13.
become that way. When we toss the high level of the average value 24 monitor signals and the low level of the monitor signal, VM = (vm
+2VL)/3. On the other hand, 7! -VL = △7, then the above formula is VM: (ΔV +3 Vt, )15 = ΔV/
It becomes S + VL. Next, the recorded information is “10000000”
1' pattern, 7u' = (yI/+ 7 VL' V8VW +V
From L' = ΔV.

W=ΔV/a +VL/. The circuit is designed so that the average values are equal, i.e. 7
Since it operates so that M=vM'.

y+, -vd sea J 7g -vtl =-! -, hv The high level and low level of the optical output vary depending on the pattern of the recording signal. As a result, the size of the recorded 9 bits fluctuates, resulting in large jitters during playback, resulting in an increase in error rate ht, and in the worst case, the pits may not be recorded.

Therefore, the present invention is intended to solve these conventional problems, and its purpose is to reduce the number of recorded signals during recording.
' and the probability of occurrence of "0"t'' - Even if a modulation method that is not above A is used, the present invention provides a semiconductor laser driving circuit in which the high level and low level are always stable and a dimensional output can be obtained.

[Means for solving problems]

The semiconductor laser driving 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. a V conversion amplification circuit; a sample timing generation circuit that generates a timing for sampling or holding the output of the F->V conversion amplification circuit based on the recording signal; and a S->V conversion amplification circuit that uses the signal from the sample timing generation circuit. a sample-and-hold circuit that samples or holds the output of the sample-and-hold circuit; a differential amplifier circuit that compares the output of the sample-and-hold circuit with a reference voltage; and a bias current supplied from the output from the differential amplifier circuit to the semiconductor laser. It is characterized by consisting of a bias current drive circuit.

[Effect]

According to the above configuration of the present invention, since the optical output monitor signal is sampled and held according to the recording signal, recording is performed using a modulation method in which the occurrence rate of /l 11 and "09 of the recording signal is not %. Even if the optical output level of the semiconductor laser is adjusted to 7.1 and low level, it is possible to always obtain a constant optical output.

〔Example〕

FIG. 1 is a block diagram of a semiconductor laser drive circuit according to an embodiment of the present invention, and FIG. 5 is a specific circuit diagram of the present invention. Components that are the same as those in FIG. 2 of the conventional example are designated by the same numbers. 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.
It is amplified by an amplifier 22 to obtain an optical output monitor signal 13. In FIG. 5, 8 is a sample timing generation circuit.

41 is a monostable multivibrator that outputs a pulse at the rising edge of the recording signal 11. Pulse time width is resistor 3
9 and the capacitor 40. Reference numeral 4 denotes a sample and hold circuit, which includes a resistor 42, a capacitor 44, a switch 43, and a buffer 45. The switch 43 is made up of a device such as an analog switch, and is turned on or off by the control signal 12. The time constant during sampling is a value given by τ-, +OR, where R is the resistor 42 and C is the capacitor 44, and it also serves as a conventional low-pass filter. Note that during signal reproduction, the switch 43 remains on.

The buffer 45 has a gain of +1 and is composed of an operational amplifier or the like. The ν output switch 28 is connected to the reproduction output reference voltage 25 during signal reproduction, and is connected to the recording output reference voltage 27 during recording, and is input to the non-inverting input terminal of the differential amplifier 5.

The difference between the output 14 of the sample hold circuit 4 and the reference voltage mentioned above is taken by a differential amplifier 5 and applied to the base of a transistor 29. A bias current drive circuit is constituted by the transistor 29 and the resistor 30, and performs APC operation by controlling the bias current of the semiconductor laser 1. Since the pulse current drive circuit portion is the same as the conventional example shown in FIG. 2, a description of its operation will be omitted.

Figure 6 is a diagram showing the signal waveforms of each part of Figure 5! P
A control signal 12 for turning on/off the switch 43 of the sample-and-hold circuit 4 is generated at the timing of the rise of @Kaiheki 11. In this embodiment, when the control signal 12 is at a high level, sampling occurs, that is, the switch 43 is turned on, and when it is at a low level, it is held, that is, the switch 43 is turned off. Since the sampling time was twice the high level time of the recording signal 11 (corresponding to data ``1''), there was a long period of time between 71' and ``1'' (N
The location ol is held, and the average value pM=pH+pL of the optical output levels of 71' and "0" is monitored.

〔Effect of the invention〕

As stated above, the present invention provides the following effects. Even if the recording signal has a modulation method in which the occurrence rate of "1" and "0" is not %, the average value of the optical output can be monitored by the sample-and-hold circuit regardless of the recording signal pattern, so the optical output is always stable and constant. control is carried out +
hru. Therefore, the thickness of the recorded pit is constant,
The error rate of the reproduced signal is improved.

[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 waveform diagram of each evil signal in FIG. 2. FIG. 5 is a semiconductor laser drive circuit diagram of the present invention. FIG. 6 1-j Signal waveform diagrams of various parts in FIG. 5. 1...Semiconductor laser 2...Monitor photodiode 4...Sample number hold circuit 8...
Sample timing generation circuit and above Applicant: Seiko Epson Co., Ltd. Kuzu 1 time average 2 figure easy 4L? 7 $S diagram

Claims (1)

[Scope of Claims] a) A semiconductor laser drive circuit for an optical information recording and reproducing device that performs recording and playback using a semiconductor laser, b) a pulse current drive circuit that applies a pulse current to the semiconductor laser in accordance with a recording signal, and 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; d) a sample timing generation circuit that generates a timing for sampling or holding the output of the I→V conversion amplifier circuit according to the recording signal; →A sample and hold circuit that samples or holds the output of the V conversion amplifier circuit; f) A differential amplifier circuit that compares the output of the sample and hold circuit with a reference voltage; and g) A sample and hold circuit that samples or holds the output of the V conversion 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.