JPS63136330A - Semiconductor laser driving circuit - Google Patents

Abstract

PURPOSE:To control an optical output so that high and low level of the output are always constant by supplying a bias current to a semiconductor laser by the output of an LPF2 interrupting the output high frequency of an operational amplifier circuit. CONSTITUTION:A pulse current 18 is monitored by a monitor resistor 9, a voltage across the monitor resistor 9 is received by buffers 67, 68 having a high input impedance and the result is subjected to differential amplification by a differential amplifier circuit comprising an operational amplifier 73 and resistors 69-72. The output of the differential amplifier circuit is given to LPFs 11, 12 to obtain a pulse current monitor signal 15. In case of read, since no pulse current is conducted and the pulse current monitor signal 15 is zero. The LPFs 2, 6 are constituted by the resistor 45 and the capacitor 46 of feedback path of the operational amplifier 47 and a transistor 48 and the resistor 49 constitute a bias current driving circuit 7, from which a bias current depending on the output of the operational amplifier 78 is fed to a semiconductor laser 1. Thus, the bias current is controlled so as to make the high/low level of the optical output always constant.

Description

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

[Conventional technology]

In a nine-optical information storage/reproduction device that uses a semiconductor laser as a light source, the optical output h of the semiconductor laser is reduced during information reproduction.
; Controls the bias current supplied to the semiconductor laser so that it is kept constant (hereinafter referred to as APO: Auto
atic Power Control). Also, when recording information, the semiconductor laser is pulse-driven using write data in such a way that a pulse current is superimposed on a DC bias. Further, the APO at this time is generally controlled so that the average value of the optical output of the semiconductor laser is constant.

FIG. 2 is a block diagram of a conventional semiconductor laser drive circuit. The optical output of the semiconductor 1 is the monitor photodiode 2.
is monitored and detected as a current signal. (2) The optical output monitor signal 13 is obtained by converting and amplifying the signal into a voltage value in the →V conversion amplifier circuit 3. The difference between this signal and the reference voltage 7 generated by the reference voltage generation circuit 4 is set by the differential amplifier circuit 30, and an error signal between the next optical output and the current optical output is obtained.

This error signal passes through a low-pass filter 6, and a bias current drive circuit 7 controls the bias current applied to the semiconductor laser 1 so that the optical output h is constant. A read signal 22h; from a terminal 21; a write gate signal 24 from a terminal 23; a write data 26 from a terminal 25; and an erase signal 28 from a terminal 27. Based on these control signals, four single voltage generating circuits generate a reference voltage. When recording information (
At write time (hereinafter referred to as write time), write data 26h is input to the pulse current drive circuit 8, and a pulse current flows through the semiconductor laser 1. APO during writing is semiconductor laser 1
This is done by controlling the bias current so that the average value bt of the optical output is constant.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology, if the probability of occurrence of write data 11 and "O' is not H at the time of writing, even if the average value PM of the optical output does not change, as shown in FIG. PL and high level are pL and pl, respectively.
It changes to K. For example, such light data is
This occurs when attempting to record a 2-7 modulated signal using the NR2 (corresponding to 6-"1' with bits, h"-5" corresponding to 0' without bits) system. 2-7 modulation Two to seven "01s" can be placed between "11" and "1'." Therefore, depending on the data pattern after modulation, the high level and low level will fluctuate even if the average value of the optical output does not change. In particular, the optical output h: Since high-level flK bits are formed, if this changes, the size of the recorded bits will change, and during signal reproduction, the jitter will increase and the error will increase.
However, in the worst case, it may become impossible to record bits.

Therefore, the present invention solves these conventional problems, and its purpose is to use a modulation method in which the probability of occurrence of write data #11 and "0" is low at the time of writing. An object of the present invention is to provide a semiconductor laser drive circuit that can control the output high level and low level h so that they are always constant.

[Elaborate means to solve problems]

The semiconductor laser drive circuit of the present invention includes an a reference voltage generation circuit that generates a voltage; a pulse current drive circuit that applies a pulse current to the semiconductor laser according to write data; a monitor resistor that monitors the pulse current; and an amplifier circuit that amplifies the output of the monitor resistor. a low-pass filter 1 that cuts high frequencies in the output of the amplifier circuit, an M-type T→V converter amplifier circuit, the reference voltage generation circuit, and an operational amplifier circuit that performs calculations on the respective outputs of the low-pass filter 1; It consists of a low-pass filter 2 that filters out the high frequency output from the operational amplifier circuit, and a bias current drive circuit that supplies a bias current to the semiconductor laser using the output of the low-pass filter 2! ! ! ! be a sign.

[Effect]

According to the above configuration of the present invention, in order to monitor the pulse current applied to the semiconductor laser based on the write data and generate the reference voltage at the time of writing, it is possible to monitor the pulse current applied to the semiconductor laser based on the write data, regardless of the probability of occurrence of 11 and "01" in the write data. APO is performed when the high level and low level of the optical output of the LD are always constant.

〔Example〕

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

First, various control signals and the signal processing circuit 13 will be explained. FIG. 5 shows a timing diagram of input/output signals. Terminal 21
When making the 22 semiconductor lasers emit light (read, write).

The write gate signal 24 inputted from the terminal 23 is set to "H" during double-angle writing, and otherwise becomes "L'".The write data 26 is inputted from the terminal 25. The write data 26 becomes "Hl" during bit recording. The erase gate signal 428#-t inputted from the terminal 27 becomes "Hl" during erasing, and otherwise becomes "Ll". The control signals described below are generated from the above input signals. The signal 31 is the same as the read signal and controls the switch 38. The signal 29 controls the switch 51 of the pulse current drive circuit 8. signal 3
The current that drives the semiconductor laser of the pulse current drive circuit 8 is turned on and off.

Next, the operation during signal reproduction will be explained. The optical output of the semiconductor laser 1 is monitored by a monitor photodiode, and the obtained photovoltaic current signal is used to generate an optical output monitor signal 13 in a 1→V conversion amplifier circuit 3 (the part surrounded by a dotted line in FIG. 4). An operational amplifier 32 and a resistor 33 perform I→V conversion, and an inverting amplifier composed of an operational amplifier 35, a resistor 36, and a resistor 37 matches the dominant power and the gain. The operational amplifier circuit 5 calculates the difference between the optical output monitor signal 13 and the reference voltage 14. The switch 38 is defined as being connected to the reference voltage - when the control signal 31 is "H1" and connected to FiGND when the control signal 31 is "L7".

Here, the operational amplifier circuit performs a 5-digit operation.

Error signal 40 = Curtain single voltage 14 + Pulse current monitor signal 15 -4. Output monitor signal 13 (1) Since no pulse current flows during reading, the pulse current monitor signal 15 is low. A low-pass filter 2 is configured by a feedback resistor 45 and a capacitor 46 of the operational amplifier 47. A bias current drive circuit 7 is constituted by a transistor 48 and a resistor 49, and supplies a bias current determined by the output of an operational amplifier to the semiconductor laser 1.

Next, the operation of the circuit during writing will be explained.

A portion 8 surrounded by a dotted line in FIG. 4 is a pulse current drive circuit. The switch 51 is short-circuited (ON) when the control signal 29 is 9H1, and is open (OFF) when the control signal 29 is "Ll". Therefore, it is ON during writing, and the reference voltage v2h is applied to the non-inverting input terminal of the operational amplifier 54. ”-applied. A current source is composed of an operational amplifier 54, a resistor 55, a resistor 56, and a transistor 56, and its current value IP is as follows.

Engineering p = R1? /V! ”−・
-" (2). The inverter 60 is of an open collector type, such as TTL's 74L S06, and the inverter is of an open collector type, such as TTL's 74LSO7. Write data 30 The inverter 60 and the buffer 61 are turned on and off alternately.Write data 30h: "When Hl, the output of the inverter 60 is on and the output of the buffer 61 is off. The voltage is the divided value, and the transistor 590 pace becomes 'Jao. Also, when the write data 30 is “Ll”, the above is reversed and the transistor 580 pace yoc,
The base qOQ of the transistor 59 is connected to the resistor 64 and the resistor 65.
The partial pressure is divided into a ratio value. As a result, the current P is switched and flows alternately to the semiconductor laser 1 and the resistor 66.

Next, pulse current monitor signal generation will be explained. Pulse current 18 is monitored by monitor resistor 9. Connect both ends of the monitor resistor 9 to high input impedance buffers 67 and 68.
Operational amplifier 73, resistors 69, 70, 71.72
Differential amplification is performed using a differential amplifier circuit consisting of By passing the output of the differential amplifier circuit through 11 low-pass filters 1, a pulse current monitor signal 151! I: Obtained. In addition,
Since the low-pass filter 1 is a general passive or active type, the specific circuit is omitted, but it includes a monitor photodiode 2 and an l-4v conversion width circuit! (The response will be the same as that of the IC.)

FIG. 6 shows the signal waveforms of each part. The driving current of the semiconductor laser 1 is 19 times, and the pulse current factor a is added to the bias current, resulting in a T-type. Optical output monitor signal is light data 30ht
When #L1, it becomes VL, and when '11'(1'), it becomes self. Peak value vp hz of pulse current monitor signal 15.

The gain of the amplifier circuit 10 is adjusted so that qp=VH-VL...-(3). Since the five operational amplifier circuits operate busily as shown in equation (1) above, the error signal V value is vx = vl + vp - vsi = (4). 7. +7p becomes the reference voltage, and the error signal 7m does not contain a component due to "H" of the write data 30, but follows the fluctuation of the input of the bias portion of the optical output.

〔Effect of the invention〕

As mentioned above, according to the present invention, the following effects are obtained +11; 4. It is caused by of light data.

Even when recording is performed using a modulation method in which the probability of occurrence of "19" and "Of" is low, such as a 2-7 modulation method, the pulse current driven by the write data is monitored to generate a reference voltage and perform APO. , a constant light output is always obtained. Therefore, the jitter when reproducing the recorded 9 bits is reduced, and the read data error hz is reduced. Furthermore, as shown in Figure 7, even if the same data string is recorded using the NRZ method (with pits f, : /l I II, no pits ^; "corresponds to OI"), the NRZ-1 method (raw data ”1
' to change the write data from "1" to 01 and "01 to 11"
Even if recording is performed using the inverting method, since the reference voltage 1 is created according to the write data, the recording can be completed without any problem. For the same reason, the write data modulation method hZ
Even if the 2-7 modulation is changed to another method such as MFM modulation or 5-tO modulation, and even if the write data transfer speed is increased, recording can be performed without problems.

In addition, it is necessary to change the optical output of the semiconductor laser during recording, for example, between the inner and outer circumferences of the recording medium; in some cases, conventionally, in addition to changing the reference voltage for current setting of the pulse current drive circuit, the output of the reference voltage generation circuit has also been changed. However, according to the configuration of the present invention, it is only necessary to use the reference voltage for setting the current of the pulse current drive circuit, and the setting is easy and the circuit configuration is simple.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a semiconductor laser drive circuit according to the present invention. Figure 2 is a schematic diagram of a conventional semiconductor laser drive circuit. Figure 3 is a current-optical output characteristic diagram of a semiconductor laser (1-P
Characteristic chart). FIG. 4 is a circuit diagram of an embodiment of the semiconductor laser drive circuit of the present invention. FIG. 5 is a timing diagram of input and output signals of the signal processing circuit of FIG. 4. FIG. 6 is a signal waveform diagram of each part of FIG. 4. FIG. 7 is a signal waveform diagram for showing the effects of the present invention. 1...Semiconductor laser 2...Monitor photodiode 3...R-4V conversion width circuit 4...Reference voltage generation circuit 5... Operational amplifier circuit 6...Low pass filter 2 7...Bias current drive circuit 8...Pulse current drive circuit 9...Monitor resistor 10...・Amplifier circuit 11...Low pass filter 1 Applicant Seiko Epson Co., Ltd. Agent Patent attorney Mogami I and 1 other person Two Toys3λ2 Body 5 Figure

Claims (1)

[Claims] a) A semiconductor laser drive circuit for an optical recording and reproducing device that records and reproduces information using a semiconductor laser, b) converting a current signal from a monitor photodiode that monitors the optical output of the semiconductor laser into a voltage value. c) a reference voltage generation circuit that generates a voltage for setting the optical output of the semiconductor laser; and d) a pulse current generated by the recording signal (hereinafter referred to as write data) to the semiconductor laser. e) a monitor resistor that monitors the pulse current; f) an amplifier circuit that amplifies the output of the monitor resistor; g) a low-pass filter 1 that cuts high frequencies of the output of the amplifier circuit; h) an operational amplifier circuit that calculates the respective outputs of the I→V conversion amplifier circuit, the reference voltage generation circuit, and the low-pass filter 1; i) a low-pass filter that cuts high frequencies of the output of the operational amplifier circuit. 2. j) A semiconductor laser drive circuit comprising: a bias current drive circuit that supplies a bias current to the semiconductor laser using the output of the low-pass filter 2.