JPH033126A - High frequency superimposing circuit for driving laser diode - Google Patents

Abstract

PURPOSE:To stabilize an action at the time of the switching of the driving mode of a laser diode in reading and writing by providing a voltage lowering means to lower a power voltage by the degree of a prescribed voltage in parallel to a switching transistor. CONSTITUTION:The voltage impressed to a high frequency generating circuit 3 is changed according to the turn-on and -off of a switching transistor 4. Name ly, at the time of reading, the transistor 4 is turned on, a voltage V-Vcc to be oscillated at normal level and frequency is given to the high frequency gener ating circuit 3, and a high frequency superimposition is applied to a laser diode driving current I. In the write mode, the transistor 4 is in an off-condition, a power voltage V-2Vd lowered by the voltage lowering means composed of diodes 5 and 6 provided in parallel on the transistor 4 is impressed to the high frequency generating circuit 3, and the high frequency oscillating circuit 3 is made into an oscillating condition at a small level. When the switching from the turn-off to the turn-on, the shift to the oscillating condition at a rated level and with a rated frequency can be executed within several mus.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement in turning on high frequency superimposition related to the laser diode drive of an optical disk drive, and more particularly to improving the response when turning on and off high frequency superposition.

<Prior art> In the laser diode drive of an optical disk drive, in order to reduce the influence of the return light from the optical disk, high frequency superimposition is applied to the laser diode drive current I (DC level) during reading, and the rated voltage is reduced during writing. In order to prevent this from being exceeded, the high frequency superposition is cut off.

The circuit for high frequency superposition (referred to as high frequency superposition circuit) is
It has an oscillation circuit of around 700 MHz, and a conventional example thereof is shown in FIG. In the figure, laser diode 1
A predetermined laser diode drive signal is applied to the device during reading or writing, but a high frequency signal is also applied from a high frequency oscillation circuit 3 via a capacitor 2.

A power supply voltage 5 is supplied to this high frequency oscillation circuit 3 via a switch 4 . The superimposition is turned on and off by supplying (applying) or stopping (not applying) the power supply voltage.

<Problems to be Solved by the Invention> However, from the perspective of an optical disc, this high frequency superimposition on/off is required to be switched within the number 88, but in the conventional on/off method of applying power supply voltage, There is a problem in that the operation of the oscillation circuit is unstable in terms of frequency and amplitude, and this affects the operation immediately after switching to the read mode.

The present invention has been made in view of the above points, and its purpose is to provide a high frequency superimposition circuit whose operation is stable when switching the drive mode of the laser diode (high frequency superposition on/off) during reading and writing. It's about doing.

Means for Solving the Problems> To achieve the above object, the present invention comprises: a high frequency oscillation circuit that oscillates with a predetermined amplitude and frequency when a power supply voltage is applied and outputs the high frequency signal; When it receives voltage, it is turned on in read mode and turned off in write mode. The present invention is characterized in that it includes a switching transistor that supplies a +W voltage, and a voltage drop means connected in parallel with the switching transistor to drop the applied power supply voltage by a predetermined voltage and apply it to the high frequency oscillation circuit.

Effects> In the present invention, in the write mode, the switching transistor is in an off state, and the high frequency oscillation circuit continues to oscillate with a small amplitude due to the application of the power supply voltage lowered by the voltage lowering means. In the read mode, high-frequency oscillation is performed at a predetermined amplitude and frequency by the power supply voltage applied through the switching transistor in the on state.

Furthermore, the power supply voltage applied to the high frequency oscillation circuit rapidly changes to a predetermined voltage when switching to the write mode and read mode, respectively, so that the operation immediately after the mode switching is not adversely affected.

<Example> The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment of a high frequency superimposing circuit for driving a laser diode according to the present invention. In the figure, parts equivalent to those in FIG. 4 are given the same reference numerals. 4 is a switching transistor, and a power supply voltage (+V) is applied to the high frequency oscillation circuit 3 via this switching transistor 4. Diodes 5 and 6 are connected in series in the forward direction, and are connected in parallel with the transistor 4, serving as voltage drop means for obtaining a predetermined voltage drop. A capacitor 7 is connected in parallel to the high frequency oscillation circuit 3, and is a bypass capacitor added to prevent noise generated when the transistor 4 is switched.

With the above configuration, the switching transistor 4 is turned on and off.
The voltage applied to the high frequency oscillation circuit 3 changes depending on the off state. In other words, when the transistor 4 is on, a voltage VVce (sat) is applied to the high frequency oscillation circuit 3 so that it oscillates at a specified level and frequency (VCC must be adjusted to achieve such a level and frequency). Note that Vce (sat) is the collector-emitter saturation voltage when the transistor is turned on).
When the transistor 4 is off, the high frequency oscillation circuit 3 receives the power supply voltage dropped by the voltage F means, that is, V2Vd.
(Vd is the forward voltage of diodes 5 and 6, approximately 0
, 7V) or is applied as the power supply voltage. This V-2Vd
When the power supply voltage is applied, the high frequency oscillation circuit 3 continues to oscillate, but its amplitude level is reduced.

Reference numeral 8 denotes an inverter which inverts the human-powered read (READ) and write (WRITE) signals, and its output is pulled up to the power supply voltage by a pull-up resistor 9 and guided to the base of the switching transistor 4. At the time of reading, the output of the inverter 8 becomes LOW level, and the base potential of the transistor 4 is set to LOW level, thereby turning on the collector-emitter of the transistor 4. Conversely, during writing, the output of the inverter 8 becomes HIGH level, raising the base potential of the transistor and turning it off.

The operation in such a configuration will be explained next with reference to the waveform diagram in FIG.

(A) At the time of reading (when high frequency superposition is on) The switching transistor 4 is turned on, and the high frequency oscillation circuit 3 is supplied with the power supply voltage V − as shown in FIG. 2(b).
V ce (sat) is applied, and the device oscillates at a specified level and frequency as shown in part A in FIG.

(B) At the time of writing (when high-frequency superimposition is off) The switching transistor 4 is turned off, and the high-frequency oscillation circuit 3 is connected to the power supply voltage V-2 as shown in FIG. 2(b).
Vd is applied, resulting in a low-level oscillation as shown in part B of FIG. 2(c) (the oscillation continues).

For example, if we take an IC whose power supply voltage rating is +5V as a high frequency oscillation circuit, it is sufficient to apply a voltage that is approximately 1.5V lower than the rated voltage as the off-state voltage. It has been confirmed that when switching from OFF to ON under such conditions, the state shifts to oscillation at the rated level and rated frequency within about 88 seconds.

In addition, if the 71rI5 [pressure is completely zero when off as in the conventional case, there is a transition state from off to on when it is turned on, as shown in Figure 2 (d) (part C). ), during this time the high frequency superimposition is not performed correctly, causing disturbances in the read signal from the disk, and the level continues to be unstable.

FIG. 3 shows a further improved embodiment. In the embodiment shown in FIG. 1, when the transistor 4 switches from off to on, the high frequency oscillation can quickly shift to a stable state, but when the transistor switches from on to off, the bypass capacitor 7 is charged. It may take some time for the voltage to drop to V-2Vd due to self-consumption of the high-frequency oscillation circuit 3. However, at this time, the mode has already shifted to light mode, and if laser diode 1 is driven with a large current, there is a risk that the attenuating high-frequency signal will be added to that current and the rated current of the laser diode will be exceeded. There is sex.

For this reason, it is necessary to quickly switch the voltage applied to the high frequency oscillation circuit even when the transistor is switched from on to off. FIG. 3 shows a circuit suitable for such a case. The difference from Figure 1 is that as a voltage drop means,
The difference is that an on/off drive circuit 30 is used in place of the ρ diodes 5, 6 and capacitor 7 shown in FIG. The on/off drive circuit 30 has the following configuration. A series-connected resistor 34, 35 that conducts the power supply voltage +V is connected to the collector of the switching transistor 33, which turns on and off in response to a read/write signal applied via the inverter 31, that is, turns off when reading and turns on when writing. and a variable resistor 36 connected in parallel to the switching transistor 4 and a capacitor 35 connected in series thereto.
is connected in parallel to the resistor 34.

According to such a configuration, when switching from the write mode to the read mode, the switching transistor 33 is turned off and the operation is similar to that of the above embodiment, or when switching from the read mode to the write mode, the switching transistor 33 is turned off. Although the switching transistor 4 is turned off, the switching transistor 33 is turned on, and the voltage Vcc applied to the high frequency oscillation circuit can be rapidly lowered to a predetermined voltage. Note that this predetermined voltage is adjusted and set in advance by the variable resistor 36.

<Effects of the Invention> As explained in detail above, when turning on and off the high frequency superimposition in driving the laser diode of an optical disk drive, the power supply voltage of the high frequency oscillation circuit is lowered when turned off.
By lowering the amplitude level (to a level where the peak value of the laser diode drive current during writing does not exceed the rated current of the laser diode) and continuing the oscillation state, when switching to the on state, Transition to a stable state occurs quickly. As described above, according to the present invention, there is an effect that stable high frequency superimposition can be turned on and off by adding a simple circuit.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of a high frequency superimposing circuit for driving a laser diode according to the present invention, Fig. 2 is a waveform diagram, and Fig. 3 is a waveform diagram.
This figure is a diagram showing another embodiment of the present invention, and FIG. 4 is a diagram showing an example of a conventional high frequency superimposing circuit. 1... Laser diode 2, 7... Capacitor 3... High frequency oscillation circuit 4... Switching transistor 56... Diode 8... Inverter 9...
・Resistance patent Applicant: Yokogawa Electric Corporation・Φ−

Claims (1)

[Scope of Claims] A high-frequency superimposition circuit that adds a high-frequency signal to a laser diode drive signal, a high-frequency oscillation circuit that oscillates with a predetermined amplitude and frequency when a power supply voltage is applied, and outputs the high-frequency signal; A switching transistor that receives a power supply voltage and is turned on in read mode and off in write mode and supplies power supply voltage to the high frequency oscillation circuit, and a switching transistor that is connected in parallel with this switching transistor and reduces the applied power supply voltage by a predetermined voltage. A high-frequency superimposition circuit for driving a laser diode, characterized in that the high-frequency superimposition circuit for driving a laser diode is provided with voltage dropping means for applying the voltage to the high-frequency oscillation circuit.