JPS62286292A - Laser diode driving circuit - Google Patents

Abstract

PURPOSE:To obtain a constant optical pulse output, by sampling the output of a photodetector element in writing by a sampling circuit, and controlling the amplitude of a variable-current amplifying circuit by the output of a comparing and controlling circuit, in which the output of the sampling circuit is compared with a reference value. CONSTITUTION:The output current from a photodetector element 12 is switched to a sampling circuit by a switching circuit 13. A bias-current controlling circuit 14 stops the output of the control data. A bias-current output circuit 15 continues the output of the bias current based on the control data immediately before. The sampling circuit 16 converts the output current of the photodetector element 12, which is switched with the switching circuit 13, into a voltage value. The value is synchronized with a clock signal CLK (a) and sampled. The result is compared with the converted voltage value of a reference current IM in a comparing and controlling circuit 17. The current amplification factor of a variable-current amplifying circuit 10 is controlled so that the optical output of a laser diode 11 becomes constant even in writing. As a result, the pulse driving current of the laser diode is changed at a high speed from Ip'1 to Ip'2. The optical output L2 of the laser diode in writing is always constant.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention Industrial Application Field The present invention provides a laser diode for use in optical discs, etc.
The present invention relates to a laser diode drive circuit that drives a laser diode.

BACKGROUND ART FIG. 3 shows the configuration of a conventional laser diode drive circuit for an optical disk. In FIG. 3, numeral 30 is a current amplification circuit that converts laser diode drive data into a pulse drive current and outputs it. 31 is a laser diode. 32 is a photodetection element that outputs a current according to the optical output of the laser diode. 33 outputs a bias current that keeps the optical output of the laser diode constant according to the output current of the photodetector element 32 when a read signal of the optical disk is output, and when a write signal is output, the write signal is output. This is a bias current control circuit that continues to output the bias current of the laser diode even if it is output at the time of the read signal immediately before the signal is output.

Next, the operation of the above example will be explained with reference to the characteristic diagram shown in FIG. In Figure 4, P. 1 is the initial current-light output characteristic of the laser diode.

The DC-light output percentage is P. , is the drive current waveform of the laser diode at field P. Next, only the threshold current of the laser diode changes, and the current-light output characteristic changes from Po to P.

2, when the optical disk read signal is output, the bias current control circuit 33 shown in FIG. 3 changes the output current of the laser diode as shown in FIG. Bias current Ib, to Ib
Change to 2.

When the write signal is output, the bias current from the previous read signal continues to be output, so Ib in Figure 4 does not change, and the current amplification factor of the current amplification circuit 3° in Figure 3 is constant, so the pulse The financial current Ip+ does not change, and the driving current of the laser diode changes from 1 to D2 as shown in FIG. 4 due to the operations during reading and writing. As a result, the optical output of the laser diode is controlled to be constant P.

In this way, even with the above conventional laser diode drive circuit for optical disks, the optical output of the laser diode can be controlled to be constant even if only the threshold (F! current) of the laser diode changes and the current-optical output characteristics change. .

Problems to be Solved by the Invention However, in the conventional optical disk laser diode drive circuit described above, the threshold current and differential quantum efficiency of the laser diode change together due to changes in temperature and deterioration of the element due to long-term use. , laser diode current −
When the optical output characteristics change, even if the bias current can be controlled by the bias current control circuit, the current amplification factor of the current amplifier circuit is constant, so the pulse drive current remains constant, and as a result, the expected constant optical pulse output will no longer be obtained.

The present invention solves these conventional problems, and aims to provide a laser diode drive circuit for optical disks that is excellent in driving laser diodes whose current-light output characteristics vary. It is something.

Means for Solving the Problems In order to achieve the above object, the present invention monitors the output of a laser diode with a photodetection element, obtains a bias current according to the output of the photodetection element from the monitor output, and
The output of the photodetecting element is sampled and compared with a reference value, the pulse current from the variable current amplifier circuit is controlled by the comparison output, and the laser diode is driven by the pulse current and bias current. be.

Operation The present invention has the following effects due to the above-described configuration. In other words, when the current-optical output characteristics change due to changes in the threshold current of the laser diode, it is possible to obtain a constant optical output of the laser diode by controlling the bias current, and the differential quantum efficiency of the laser diode changes. When both change and the current-light output characteristics change,
By applying both the bias current and the pulsed current to the prick, the light output of the laser diode can be kept constant and germs can be sterilized at high speed.

Embodiment FIG. 1 shows an embodiment of the present invention. In FIG. 1, numeral 10 is a variable current amplifier circuit that converts laser diode drive data DIN into a drive current and outputs the drive current. 11 is a laser diode. 12 is a laser diode 11
Laser diode 1 outputs a current according to the optical output of
This is a photodetection element for monitoring the output of 1. Reference numeral 13 denotes a switching circuit that switches the output current of the photodetector 12 to the R side when a read signal from the optical disc is being outputted, and to the W side when a write signal is outputted. Reference numeral 14 denotes a bias current control circuit that outputs control information for the bias current of the laser diode in response to the output current of the photodetector element 12 switched by the switching circuit 13 in response to a readout signal. This circuit does not output sterilization information when the output current of the photodetecting element 12 is switched to the W side by the switching circuit 13 in response to a write signal. Reference numeral 15 denotes a bias current output circuit that outputs a bias current according to side tilt information from the bias current control circuit 14 to keep the optical output constant during reading. This circuit continues to output the bias current according to the immediately preceding control information even if the side leg information is no longer output from the bias current control circuit due to the write signal. 16 converts the output current of the photodetector 12 switched by the switching circuit 13 according to the write signal into a voltage, and outputs the value as a clock signal C.
This is a sampling circuit that samples in synchronization with LK. 17 controls the pulse drive current of the laser diode at high speed by comparing the sampling value in the sampling circuit 16 with the voltage conversion value of the reference current generator and controlling the current amplification factor of the variable current amplifier circuit. This is a comparison control circuit that keeps the optical output of the laser diode constant during writing.

Next, the above embodiment will be explained. In Figure 2, P.

', is the initial current-light output characteristic of the laser diode, and Dl is the driving current waveform of the laser diode when the current-light output characteristic is P,'. Next, the current-light output characteristic of the laser diode changes to P due to changes in threshold current and differential quantum efficiency. ', to P. '2 and a readout signal for the optical disk is being output, the output current of the photodetecting element 12 is switched by the switching circuit to the R side, that is, to the bias current NllH circuit 14 side, as shown in FIG. Therefore, the bias current control circuit 14 outputs control information to the bias current output circuit so that the optical output of the laser diode during readout is constant according to the output current. The bias current output circuit outputs a bias current according to the control information. As a result, the bias current changes from IbH to 1bg as shown in FIG. 2, so that the optical output of the laser diode during reading remains constant. Also, the current-light output characteristic is P. '2 and the write signal is issued after the optical disc start signal,
In FIG. 1, the output current of the photodetector element 12 is switched by a switching circuit 13 to the W side, that is, to the sampling circuit side. At this time, the bias current control circuit 14 stops outputting control information and the bias current output circuit 15 continues to output the bias current based on the immediately previous control information. That is, Ib', which is changed from Db' in FIG. 2, is output as is. The sampling circuit 16 in FIG. 1 converts the output current of the photodetecting element 12 switched by the switching circuit 13 into a voltage, and samples the value in synchronization with the clock signal CLK.

The sampled value is compared with the reference current value in the control circuit 17. The current amplification factor of the variable current amplifier circuit 10 is controlled so that the optical output of the laser diode remains constant even during writing by comparing with the voltage conversion value of . As a result of this, the second
As shown in the figure, the pulse drive current of the laser diode is
It changes rapidly from p' to p'2, and the optical output L2 of the laser diode during writing is always constant.

According to the above embodiment, the switching circuit 13 switches the output current of the photodetecting element 12 depending on the read signal and the write signal, the bias current side circuit 14 controls the light output at a constant level during reading using the output current, and the bias current Since it is equipped with an output circuit, a sampling circuit 16, a comparison control circuit 17, and a variable current amplification circuit that control the optical output at high speed and constant during writing, the current of the laser diode - optical Output characteristics are P. Even if the bias current changes from 1' to P;, the bias current b is controlled to 1b'2, and the pulse 1 drive current 1p' is controlled to I p't, so the optical output during reading and writing. This has the effect of keeping the optical output L2 constant at all times.

Note that the bias current control circuit 14 and the bias current output circuit 15 constitute a bias current control child.

Effects of the Invention As is clear from the above embodiments, the present invention allows the bias current and pulse to be maintained even if the threshold current and differential quantum efficiency of the laser diode used in the optical disk change, that is, the current-optical output characteristics change. Since the driving current can be controlled (2), it is possible to perform high-speed reading and writing and obtain the necessary constant optical output.

In particular, since it uses a sampling circuit synchronized with a clock signal, it has the advantage of being able to detect and respond to changes at high speed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a laser diode circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of the circuit in FIG. 1, and FIG. - Block diagram illustrating an example of the diode circuit, No. 4
This figure is a waveform diagram for explaining the operation of the circuit of FIG. 3. DESCRIPTION OF SYMBOLS 10... Variable current amplifier circuit, 11... Laser diode, 12... Photo detection element, 13... Switching circuit, 14... Bias current control circuit, 15... Bias current output circuit, 16 ...sampling circuit, 17.
...Comparison control circuit, 30...Current amplification circuit, 31...
・Laser diode, 32... Photodetection element, 33...
・Bias current control circuit. Name of agent: Patent attorney Toshio Nakao and one other person Figure 3: 4

Claims (1)

[Claims] A variable current amplifier circuit for applying a pulse drive current to the laser diode when driving the laser diode in response to an input pulse during writing, a photodetection element for monitoring the optical output of the laser diode, and the photodetection element. bias current control means for controlling a bias current to be superimposed on the pulse drive current according to the output of the pulse drive current, and a sampling circuit samples the output of the photodetecting element during the writing, and compares the output of the sampling circuit with a reference value. A laser diode drive circuit, further comprising a comparison control circuit for controlling the amplification degree of the variable current amplification circuit based on the output of the comparison control circuit.