JPH0514973B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a sample and hold circuit.

(Prior Art) A sample-and-hold circuit having a mode of holding an input signal and a mode of outputting an input signal following the input signal will be explained using an example of a light amount control device of a magneto-optical disk memory device.

A magneto-optical disk memory device is an optical recording/reproducing device that uses a magnetic film having an axis of easy magnetization in a direction perpendicular to the film surface as a recording medium, and performs recording, reproduction, or erasing by irradiating the magnetic film with a laser beam. The recording and reproducing method of the magneto-optical disk memory device will be explained below.

When recording, information is recorded as follows.
When a laser beam focused to a diameter of about 1 μm is intensity-modulated according to an information signal and irradiated onto the surface of a magnetic film, the temperature of the magnetic film locally increases. Since the coercive force decreases in the area where the temperature has increased, if an auxiliary magnetic field is applied from the outside at the same time, the direction of magnetization is reversed and information is recorded.

On the other hand, during reproduction, the recorded magnetic film surface is irradiated with linearly polarized laser light of a weaker intensity than during recording.
Then, the reflected light has a tilted plane of polarization due to the magneto-optical effect (Kerr effect) of the magnetic film. This slope is converted into the intensity of light through an analyzer, and when detected by a photodetector, it becomes a reproduced signal.

The intensity of the laser beam is divided into two levels, high and low, as described above.
two output levels are required. The high output intensity level is used during recording (erasing), and the low output intensity level is used during playback.

A semiconductor laser that emits a laser beam has temperature characteristics, and its intensity varies depending on the ambient temperature. If the high output intensity fluctuates during recording of information, insufficient or excessive information may be written to the recording medium, and the reliability of reproduced information deteriorates. On the other hand, if the low output intensity fluctuates during information reproduction, the S/N ratio of the reproduced signal deteriorates. Therefore, it is necessary to stabilize the laser light intensity at both high and low output levels.

Therefore, a light amount control device shown in FIG. 3 was proposed. This is provided with two current sources 8 and 9 that supply driving current to the semiconductor laser 1. During information reproduction, the semiconductor laser 1 is driven only by the drive current I _R from the low-output bias current source 8. Further, when recording (erasing) information, high output intensity is obtained by adding the drive current I _W from the high output pulse current source 9 to the drive current I _R.

Now, automatic light output control (so-called APC) for obtaining a constant output light intensity is performed as follows. First, automatic light output control of the light amount is performed for low output light intensity. Next, when the output is high, by holding the current value I _R at the low output and adding the current I _W for high output to this, automatic light output control is apparently realized even when the output is high. This is because in the drive current vs. optical output curve of a semiconductor laser, only the threshold value changes with changes in ambient temperature, the slope above the threshold does not change, and only the low output current exceeds the threshold. This is because if it is controlled to a certain value, automatic light output control at high output can be realized simply by adding a constant current for high output.

Some automatic light output control uses a sample and hold circuit. Next, an example of automatic optical output control (APC) using a conventional sample and hold circuit will be described below with reference to the drawings. First, control during information reproduction, ie, low output, will be explained. In Fig. 3, the output light intensity of the semiconductor laser 1
P ₂ is constantly monitored by the photodetector 2 and converted into a voltage signal V _a2 . This monitor signal V _a2 is
The differential amplifier 3 compares the reference voltage V _b2 with the output voltage V _C2 (=V _b2 - V _a2 ), which passes through the low-pass filter 5 and becomes the voltage V _d2 , which is then output to the switching circuit 7.
The voltage V _e2 (=V _d2 ) is applied to the bias current source 8 via
be guided by At low output, the switching circuit 7 is switched to output the output voltage V _d2 of the low-pass filter 5 as is. The bias current source 8 controls the bias current I _R based on this optical intensity data V _e2 so that the output V _c2 of the differential amplifier 3 becomes 0, and keeps the low output intensity P ₂ of the semiconductor laser 1 constant. keep.

Next, when recording (erasing) information, that is, at high output, the output voltage V _d2 of the low-pass filter 5 is stored in advance in the memory circuit 6 as data with low output intensity, and the switching circuit 7 is connected to the memory circuit 6.
Switch to the side. Then, a recording pulse current (erase current) I _W is added to the bias current I _R by a high-output pulse current source 9 . When recording (erasing) information, the automatic light output control for low output is frozen in order to avoid lowering the low output intensity in response to the high output intensity. By adding a current for high output, automatic light output control can be realized even at high output.

Here, a circuit 10 consisting of a low-pass filter 5, a memory circuit 6, and a switching circuit 7 is composed of two
There are two modes: one is to pass the input signal through a low-pass filter and the other is to output the signal.
One is a so-called sample-and-hold circuit which has a mode in which this is stored in a memory circuit 6 and its output is held.

(Problems to be Solved by the Invention) In the configuration of the conventional sample and hold circuit 10,
Since the transient response characteristics of the low-pass filter 5 remain,
Light intensity control for both high and low output cannot be achieved instantly.
This will be explained using FIG. 4.

First, the optical output intensity _P2 of the semiconductor laser 1 in Fig. 3 is stabilized in advance by automatic optical output control during playback, and high output intensity is added during recording (erasing), resulting in a waveform as shown in Fig. 4. Become.
Waveforms V _a2 , V _b2 , V _c2 , V _d2 , V _e2 and timing signals S ₁ , S ₂ shown in FIG. 4 correspond to those with the same symbols shown in FIG. 3. The output V _a2 of the photodetector 2 is the optical intensity P ₂ converted into a voltage signal, and is compared with the reference voltage V _b2 in the differential amplifier 3, and the difference is calculated.
V _c2 (=V _b2 −V _a2 ) is output. This difference V _c2 is
The signal is input to the low-pass filter 5 in the sample-and-hold circuit 10. The low-pass filter 5 passes a low frequency range corresponding to intensity fluctuations due to temperature characteristics of the semiconductor laser. low pass filter 5
The output voltage V _d2 exhibits a transient response as shown in FIG. This output voltage is guided to a memory circuit 6 and a switching circuit 7. In the memory circuit 6,
When the memory timing signal _S1 is at a high level, the input signal is recorded and simultaneously output and held. In the switching circuit 7, when the switch timing signal _S2 is at a high level (during reproduction), the output voltage _Vd2 of the low-pass filter 5 is passed through as is, so automatic optical output control is performed, and when the switch timing signal S2 is at a low level (during recording (erasing)), automatic optical output control is performed. ) passes the output signal of the memory circuit 6.
Therefore, the output signal of the switching circuit, that is, the output voltage V _e2 of the sample and hold circuit 10 is
As shown in the figure, after the transition from recording (erase) to reproduction, the transient response component caused by the low-pass filter 5 remains, so the output light intensity _P2 of the semiconductor laser 1, which is controlled according to this voltage V _e2 , also has a transient response. The components remain and take the response time to stabilize.

That is, in the sample-and-hold circuit 10 surrounded by the broken line in FIG. 3, the transient response component of the low-pass filter 5 remains in the output signal of the sample-and-hold circuit itself, so that good control of the output light intensity cannot be performed. Therefore, a sample and hold circuit that does not include transient response is essential.

SUMMARY OF THE INVENTION In view of the problems of the prior art described above, an object of the present invention is to provide a sample-and-hold circuit that has a mode for holding an input signal and a mode for following the input signal in which no transient response of the filter circuit occurs. .

(Means for Solving the Problems) A sample hold circuit according to the present invention includes a memory means for storing an input signal, an input signal at one input terminal, and an output of the memory circuit at the other input terminal. comprising switching means for inputting a signal and switching and outputting the output signal of the memory means and the input signal according to the input timing signal; and filter means for processing the output signal of the switching means and outputting the processed signal to the outside; The output signal of this filter means is further connected to the input terminal of the above-mentioned memory means, and in the mode of holding the input signal, the output of the memory circuit is transmitted, and in the mode of following the input signal, the input signal is transmitted through the above-mentioned filter circuit. Output.

(Function) In the present invention, filter means is arranged after the switching means. Now, if the output value of the sample and hold circuit in the mode that follows the input signal is stored in the memory means, when the switching means is switched between both modes, the output signal of the switching means will be almost the same, so it will be easier to switch between the two modes. In this case, the output signal of the sample and hold circuit is hardly affected by the transient response.

(Example) Hereinafter, an example of a sample and hold circuit according to the present invention having a mode for holding an input signal and a mode for following the input signal will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of a sample and hold circuit according to the present invention in a portion surrounded by a broken line as an example of application to a light amount control device for a magneto-optical disk memory device. FIG. 2 is a diagram for explaining waveforms and timing signals in the circuit shown in FIG. 1.

In FIG. 1, the intensity P ₁ of output light emitted from a semiconductor laser 1 is converted into a voltage signal V _a1 by a photodetector 2 . This signal is the differential amplifier 3
is compared with the reference voltage V _b1 at the voltage V _c1 (=
V _b1 −V _a1 ) is output. The voltage V _c1 is input to the switching circuit 7 in the sample and hold circuit 4 , and its output V _d1 is converted to the voltage V _e1 via the low-pass filter 5 and guided to the bias current source 8 and the memory circuit 6 .

During information reproduction, the switching circuit 7 passes the output signal V _c1 of the differential amplifier 3, and accordingly the output current I _R of the bias current source 8 is controlled, thereby performing automatic optical output control with low output intensity. Memory circuit 6
as low output intensity data in advance.
Remember V _e1 . On the other hand, when recording information, the switching circuit 7 switches to this, and the memory circuit 6
Pass the data. This freezes the automatic light output control at low powers and avoids responding to high power intensities. Then, a pulse current _IW for high output is added from the pulse current source 9, and high output light for stable recording (erasing) is emitted.

The symbols in FIG. 2 showing waveforms and timing signals correspond to the same symbols in FIG. As shown in the figure, the output light intensity _P1 emitted from the semiconductor laser 1 is stabilized at a low output intensity by automatic light output control during information reproduction.
When recording (erasing) information, the output intensity is high. This is converted into a voltage signal V _a1 by photodetector 2, and the reference voltage is
Compared with V _b1 , V _c1 is output.

Sample and hold circuit 4 that inputs this V _c1
It will be shown below that no transient response occurs in the output V _e1 . First, during information reproduction, the sample and hold circuit 4 performs automatic optical output control (APC) through _{the voltage V c1 in} accordance with the switch timing signal S2. Next, during information recording, the memory circuit 6 stores data V _e1 of low output intensity during information reproduction in accordance with the memory timing signal S ₁ . and switching circuit 7
is switched in accordance with the negative progression trigger of the switch timing signal _S2 , and passes the output of the memory circuit 6.
(When reproducing information, V _c1 is passed through again.) Then, the output V _d1 of the switching circuit 7 becomes as shown in _FIG . This results in a waveform that does not cause transient response. Therefore, no transient response appears in the output light intensity _P1 of the semiconductor laser 1,
Stable output light intensity can be obtained instantaneously at both high and low output levels.

As described above, when the sample and hold circuit according to the present invention is used, a transient response due to a low-pass filter does not occur, and stable output light intensity can be instantaneously obtained. Further, in this embodiment, the sample and hold circuit is used only for data of low output intensity, but even when automatic light output control of high output intensity is performed separately, it can be similarly used as a sample and hold circuit for data of high output intensity.

In this embodiment, a magneto-optical disk memory is used as an example of the optical memory device, but other optical memory devices can also be used.

Although the present invention has been described with reference to a light amount control device, the present invention is not limited to these devices, and can be applied to any sample-and-hold circuit used to remove signals having different levels. For example, in the same optical memory device, automatic gain control of a reproduced signal will be taken as an example. In this case, since the gain is controlled, it is sufficient to control slow changes such as temperature changes, so the transient response of the low-pass filter becomes a problem. That is, when performing automatic gain control from the reproduction signal level, a pulse of a large level corresponding to the recording (erasing) light amount is added to the reproduction signal level during recording (erasing). Therefore, it is necessary to remove the pulses so that the automatic gain control does not respond to the recording (erase) level. Also in this case, by applying the sample and hold circuit of this embodiment, the influence of the transient response of the low-pass filter on the gain can be removed.

Further, as an example of the transient response of a filter, a low-pass filter has been shown as an example, but the same applies to a high-pass filter and the like.

(Effects of the Invention) According to the present invention, it is possible to provide a sample and hold circuit in which no transient response occurs due to a filter circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a light amount control device using a sample and hold circuit according to an embodiment of the present invention.
FIG. 2 is a diagram showing waveforms and timing signals in the circuit of FIG. 1. FIG. 3 is a circuit diagram of a light amount control device using a conventional sample and hold circuit. FIG. 4 is a diagram showing waveforms and timing signals in the circuit of FIG. 3. 1... Semiconductor laser, 2... Photodetector, 3...
Differential amplifier, 4...Sample hold circuit, 5...
...Low pass filter, 6...Memory circuit, 7...
Switching circuit, 8...Bias current source, 9...
...Pulse current source.

Claims (1)

[Scope of Claims] 1. A memory means for storing an input signal, an input signal is input to one input terminal, an output signal of a memory circuit is input to the other input terminal, and the memory is stored by an input timing signal. The switching means switches and outputs the output signal and the input signal of the means, and the filter means processes the output signal of the switching means and outputs the processed signal to the outside. a sample and hold circuit connected to the input terminal of the means for outputting the output of the memory circuit in a mode of holding the input signal and the input signal in a mode of following the input signal through the filter circuit;