JPH0656668B2 - Optical disc recording / reproducing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called DRAW type optical disc recording / reproducing apparatus using a writable disc.

Background art and its problems So-called DR using a disc that can write data
In the AW type optical disc recording / reproducing apparatus, a spiral recording track T is formed on the rotation plane of the disc (1) as shown in FIG. 1, and the recording track T has a predetermined interval in the rotation direction. And holds the address data section (2A),
A data writing unit (2S) for information data such as a video signal is sequentially and alternately provided. In the address data part (2A), predetermined address data D _A is already formed on the disk plate surface at the time of manufacturing the disk, and only the data writing part (2S) is an unrecorded part. Therefore, the user's favorite information is recorded (written) in the data writing unit (2S).

FIG. 2 is a system diagram showing an example of a main part of a laser drive circuit (10) in an optical disc recording / reproducing apparatus adopting such a DRAW system.

In the figure, (4) is a semiconductor laser portion provided in the optical head, LD is a laser diode, PD is a light receiving diode for monitoring the diode LD, and in this example is a pin diode. The laser diode LD is the DC of the driver (5) that acts as a DC bias means.
It is excited by the output (DC bias current) and its D
The laser power of the laser diode LD is controlled by the magnitude of the C bias current.

Since the current I _P flowing through the pin diode PD corresponds to the power of the laser diode LD, this current I _P is converted into a voltage by the current / voltage converter (6), and the converted voltage V _P is a voltage. in the comparator (7) is compared with a reference voltage V _R, DC bias current of the driver (5) is controlled by the comparison output. Therefore, by such a closed loop, the laser power of the laser diode LD is obtained as a constant laser power corresponding to the reference voltage V _R. That is, this closed loop acts as an automatic power control (APC) circuit (8).

The reference voltage V _R is different when writing data and when reading data, but this is based on the following reason.

That is, in the DRAW system, data writing is performed by controlling the power of the laser beam applied to the disc (1), and usually a predetermined laser power, for example 14
When mW (average value) or more, data can be written to the disc (1), and therefore, when reproducing (reading) the information data D _S and reading the address data D _A , the laser power for several minutes is more than the laser power at the writing. It is necessary to reduce the laser power to 1, for example, about 1/4 (thus, about 3 mW). Therefore, the reference voltage V _R is switched in each mode so that the laser power set as described above is obtained in each of the read and write modes.

The selection circuit (11) for the reference voltage V _R is used in the write mode as shown in the figure. A reference voltage V _RW setting circuit (12) for obtaining laser power (about 14 mW) and a reference voltage V _RR (V _RR ≈1 /) for obtaining laser power (about 3 mW) used in the read mode. 4V _RW ) setting circuit (13), and these are selected by the changeover switch (14). Which reference voltage V _RW or V _RR is selected is determined by the mode switching pulse P _S supplied to the terminal (15).

In the data writing mode, the digital signal S _V such as the video signal supplied to the terminal (16) is applied to the laser diode LD via the driver (17) to write the data D _S corresponding to the digital signal S _V. Be done.

In order to improve the S / N during playback of data D _S , 700
The data D _S may be read with the high frequency signal RF of about MHz supplied. Therefore, the laser drive circuit (10) is provided with an oscillator (18) for the high frequency signal RF, and the high frequency signal RF is supplied to the laser diode LD via the current driver (19).

Now, the relationship between the forward current I _D of the laser diode LD and the laser power P _L has the characteristic shown by the curve l ₁ in FIG. 3, and a DC bias current such that the forward current I _D becomes I _R flows. When this is done, a laser power P _L for reading (= 3 mW) is obtained, and when a DC bias current of I _W higher than I _R is passed, a laser power P _L for writing (= 14 mW) is obtained. Curve l ₂
Is a curve showing the characteristics of the forward drop voltage V _F of the laser diode LD.

As is clear from the diode characteristic curve l ₂ shown in FIG. 3, the laser diode LD has a very large impedance when the DC bias current I _D is small. Therefore, if the high frequency signal RF is supplied in such a state, The negative peak value of the voltage of the signal may exceed the reverse withstand voltage value of the laser diode LD (about -2V).

Therefore, when the data D _S is read from the disk (1) by high frequency modulation, this laser diode LD is destroyed unless a high frequency signal RF is applied to the laser diode LD after a predetermined DC bias current is passed. May occur. Thus, when the power is turned on, the DC
The laser diode LD is destroyed if the RF driver (19) for high-frequency signal RF starts up faster than the driver (5) for a moment, or if the operation of the RF driver (19) falls for a moment when the power is turned off. Will be done. Conventionally, this point is not taken into consideration, so that the probability that the laser diode LD is destroyed is extremely high.

SUMMARY OF THE INVENTION Therefore, the present invention proposes an optical disk recording / reproducing apparatus in which the laser diode LD is not destroyed in consideration of the above point.

SUMMARY OF THE INVENTION Therefore, a laser drive circuit used in an optical disc recording / reproducing apparatus according to the present invention includes a laser diode,
A driver (DC driver) acting as a DC bias means for supplying a predetermined DC bias current thereto,
A high frequency signal driver for data reading (RF driver), a first delay circuit provided in a power supply path for the CD driver, and a second delay circuit provided in a power supply path for the RF driver, The delay time of the first delay circuit is set shorter than the delay time of the second delay circuit so that the DC driver rises faster than the RF driver at least when the power is turned on in the data read mode. It was done.

Embodiment Next, an example of the optical disc recording / reproducing apparatus according to the present invention will be described in detail with reference to FIG.

In FIG. 4, the first power supply voltage (minus voltage) -B applied to the first power supply terminal (20) is applied to the DC driver via the first delay circuit (21) and the first AND circuit (22). Supplied to (5). The first delay circuit (21) is of an on-delay type which is delayed by a predetermined time τ _DC only when the power source rises and is not delayed at all when the power source falls.

Further, the second power supply voltage (plus voltage) + B applied to the second power supply terminal (23) is passed through the second delay circuit (24) and the second AND circuit (25) to the RF driver (19). Is supplied to. Similarly to the first delay circuit (21), the second delay circuit (24) is also an on-delay type circuit, and is delayed by a predetermined time τ _RF only when the power supply rises. τ _DC and τ _RF are set to τ _DC <τ _RF , and when τ _DC = 10 msec, τ _RF
Is set to about 20 msec.

A drive command signal P _ON for the laser diode LD obtained from a system controller (not shown) is connected to the terminal (27).
Is supplied to the third AND circuit (28). A monitor circuit (30) is further provided in the third AND circuit (28).
The control signal P _S from

The monitor circuit (30) monitors whether or not the laser diode LD is operating normally, and when abnormal, in this example, it drives when the required laser power in the write mode and the read mode exceeds the reference value. This circuit outputs the stop signal P _S. Therefore, the monitor circuit (30) compares the reference level V _RO and the voltage V _{P in} the read mode with the first comparator (31) that compares the reference level V _WO and the voltage V _{P in the} write mode. When the laser power is normal, the respective comparison outputs are “H” and the comparison outputs are “L” only in the abnormal condition. 33) through the third AND circuit (2
Supplied to 8).

The output of the third AND circuit (28) is supplied to the first AND circuit (22) and is also supplied to the second AND circuit (25) via the third delay circuit (34). The third delay circuit (34) is also an on-delay type, and its delay time τ _ON
Is set to be approximately equal to the first delay time τ _DC in this example.

The decoupling capacitor of the decoupling circuit (not shown) provided on the first power supply terminal (20) side is the decoupling circuit (not shown) provided on the second power supply terminal (23) side. The capacitance value is selected to be slightly larger than that of the decoupling capacitor in (1).

When the laser drive circuit (10) is configured in this way, the DC driver (5) and the RF driver are used when the power is turned on and off.
Driving and stopping are performed at different timings from (19).

First, when the power switch of the laser drive circuit (10) is turned on in the read mode of the data D _A and D _S , the first AND circuit (22) is delayed by the first delay time τ _DC from the time when the power is turned on. The first power supply voltage -B is supplied, and the second AND circuit
The second power supply voltage + B is supplied to (25) with a delay of the second delay time τ _RF . At the same time when the power is turned on, the system controller supplies the drive command signal P _ON of “H” to the terminal (27) with a probability of 50% as described later and the control signal P _S of “H” level is supplied to the third terminal. since supplied to the aND circuit (28), the time tau _DC from the power on such time
After that, the DC driver (5) is driven, and the RF driver (19) is also driven after the time τ _{RF has} passed since the power was turned on.

Since τ _DC <τ _RF , the power supply timing of the DC driver (5) is (τ _RF −
τ _DC ) is faster. Therefore, since the RF driver (19) is driven after the DC driver (5) is driven, the high frequency signal RF is supplied after the predetermined DC bias current I _W or I _R is supplied to the laser diode LD. The high frequency signal RF is not applied when the laser diode LD is in the non-biased state.

Immediately after the power is turned on, it is not known whether the drive command signal P _ON obtained from this system controller is "H" or "L" until the system controller is initialized, that is, reset. "H" or "L" has a 50% probability. Therefore, drive command signal P
_{Even when ON} is “H”, the first delay time τ _DC is slightly shorter than the reset time of the system controller so that the DC driver (5) is not driven until the system controller is reset. For example, as described above, it is selected to be about 10 msec.

When the power is completely turned on, the drive command signal P _ON is controlled by the output of the system controller, and the drive signal P is _ON during both the write mode standby and the read mode standby.
_ON is “L”.

Since the third delay circuit (34) is an on-delay type,
When the drive command signal P _ON becomes “L”, the DC driver (5)
The supply of the power supply voltages -B and + B to the RF driver (19) is cut off at the same time. On the other hand, drive command signal P _ON
Becomes "H", the power supply voltage + B of the RF driver (19) is delayed by the third delay time τ _ON from the power supply voltage -B of the DC driver (5) due to the existence of the third delay circuit (34). Stand up. As a result, the laser diode LD is supplied with the predetermined high frequency signal RF after being supplied with the DC bias current I _W or I _R.

Immediately after or during the start of the writing mode or the reading mode, or in the middle thereof, when the laser power exceeds the reference value in each mode, the control signal P _S changes from “H” to “L”.
Turns into. Therefore, at this time, the drive command signal P _ON is “H”.
However, the supply of the power supply voltages -B and + B is cut off at the same time. That is, when the laser power is abnormal, the drive command signal
The same power supply control operation is performed as when P _ON is “L”.

Since both the first and second delay circuits (21) and (24) are of on-delay type, the DC driver (5) and the RF driver (19) should be stopped at the same time when the power is off. It is considered, but since the decoupling capacitor provided on the first power supply terminal (20) side is larger than the decoupling capacitor provided on the second power supply terminal (23) side,
The DC driver (5) stops a little later than the RF driver (19).

As a result, the supply of the DC bias current I _W or I _R is cut off after the high frequency signal RF is stopped without fail, so that the high frequency signal RF is not supplied when the laser diode LD is in the non-biased state. .

As is clear from the above description of the operation, in the read mode of the data D _A and D _S , when the operating power supply is on, or the drive command signal
When P _ON becomes “H”, DC driver
Since (5) rises faster than the RF driver (19),
The laser diode LD is no longer driven in a non-biased state, and the laser diode LD can be reliably prevented from being destroyed.

Further, when the operating power supply is turned off, the DC driver (5) rises later than the RF driver (19) contrary to the above, so that the laser diode LD is not likely to be broken in this case as well.

Since the DC driver (5) and the RF driver (19) simultaneously fall when the drive command signal P _ON becomes “L” or when the laser power abnormality is detected, the laser diode LD may be destroyed at this time as well. Absent.

As described above, according to the present invention, in the optical disc recording / reproducing apparatus of the DRAW system, which is configured to read the data D _S on the disc (1) in the state where the high frequency signal is supplied,
Since the rising timing and the falling timing of the power source for the DC driver (5) and the RF driver (19) at the time of reading data are different, the laser diode LD
The destruction of can be surely protected.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a recording track, FIG. 2 is a system diagram showing an example of a conventional optical disc recording / reproducing apparatus, and FIG.
FIG. 4 is a characteristic diagram of a laser diode, and FIG. 4 is a system diagram showing an example of an optical disc recording / reproducing apparatus according to the present invention. (10) is a laser drive circuit, LD is a laser diode, (5)
Is a DC driver, (18) is a high frequency signal RF oscillator, (1
Reference numeral 9) is an RF driver, (21), (24) and (34) are first to third delay circuits, and -B and + B are operating power supply voltages.

Claims (1)

[Claims] 1. A laser diode for signal writing and reading, and a DC for supplying a DC bias current to the laser diode.
An optical system including: a driver; an RF driver that superimposes a DC bias current on the DC bias current to supply a high frequency signal to the laser diode; and a power supply unit that supplies power to the DC driver and the RF driver, respectively. A disk recording / reproducing apparatus, wherein the D
A first delay circuit provided in a power supply path to the C driver, and a second delay circuit provided in a power supply path to the RF driver, wherein the delay time of the first delay circuit is An optical disc recording / reproducing apparatus in which the delay time is set shorter than the delay time of the second delay circuit.