JPH01173475A - Reading signal amplifying circuit - Google Patents

Abstract

PURPOSE:To eliminate a noise in an unrecorded part by amplifying the output signal of a preamplifier, and making its gain variable based on the output signal of the preamplifier while the effective signal exists. CONSTITUTION:An output signal A of a preamplifier 24 is amplified by an AGC amplifier 25, binarized by a binarizing circuit 26, and made into reading data. Further, the output signal A of the preamplifier 24 is rectified by an all wave rectifier 27, an output signal B is sample and held using a sampling pulse D from a sampling pulse generating circuit 29 by a sample and hold circuit 30. The gain of the AGC amplifier 25 is controlled by an output signal E of the sample and hold circuit 30. Thus, the output signal of the AGC amplifier 25 does not become too large in the unrecorded area, and the correctly read data G can be obtained from the binarizing circuit 26.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an optical disk device (including a magneto-optical disk device)
The present invention relates to a read signal amplification circuit.

(Prior art) Figure 3 shows the RF detection (alternating current component detection)/AG of an optical disk device known from Japanese Patent Application Laid-Open No. 59-22247.
C (automatic gain control) circuit is shown.

In an optical disc device, light is irradiated from a laser onto an optical disc, and the reflected light enters a 4-segment photodetector 1. It is divided into four by a line and a dividing line perpendicular to the line. Each 2 non-adjacent portion of the 4-segment photodetector 1
The photoelectric conversion signals from the two parts are connected to the resistors R1 to R4, respectively.
are added by adders 2 and 3 via adders 2 and 3.
The output signals of 3 are added by an adder 4 and then binarized by a binarization circuit to become a digital signal. Further, the output signals of adders 2 and 3 are added by adder 5 to become a focus error signal, and the output signal of adder 4 is added by resistor R6.
A DC component is extracted by a low-pass filter 6 consisting of a capacitor C2 and a capacitor C2, and is compared with a reference level of a reference power supply 8 by a differential amplifier 7. Furthermore, the AC component of the output signal of the adder 4 is extracted by the DC blocking C3. This alternating current component is converted into a direct current signal by a rectifying and smoothing circuit 13 consisting of a diode D1, a capacitor C4, and a resistor R7, and is compared with a reference level of a reference power source 5 by a differential amplifier 14. The variable impedance elements 9 to 12 are each fourth
As shown in the figure, it is composed of a field effect transistor Q+Qz and a capacitor C8, and the DC component a from the differential amplifier 7 and the AC component C from the differential amplifier 14 are added to the gates of the field effect transistors Q, , Q. impedance changes. These variable impedance elements 9 to 12
are connected in parallel with the load resistors RL1 to RL4, respectively, and good AGC is performed on both AC and DC components of the output of the photodetector 1 by changing the impedance of the variable impedance elements 9 to 12.

However, in this RF detection/AGC circuit, the AC component extracted by the DC blocking C1 is the I D (I
dentification section, unrecorded section, and data recording section, as shown in the signal at point H shown in FIG. After being compared with the level, as shown in Figure 5C, it is low in the unrecorded area and 1
It becomes high in the 0 part and the data recording part. Since the impedance of the variable impedance elements 9 to 12 is varied by this signal C, the output signal of the adder 4 is large in the unrecorded part and becomes small in the ID part and data recording part,
As shown in the figure, the noise in the unrecorded area is amplified by a large gain. When the output signal of the adder 4 is binarized by the binarization circuit, a random noise-like digital signal is generated even in the unrecorded part other than the ID part and the data recording part, and the digital signal from the binarization circuit is This causes a problem in that the ID readout circuit and synchronization circuit that read the ID signal and generate the synchronization signal mistake the noise for the ID signal and malfunction.

(Objective) It is an object of the present invention to provide a read signal amplification circuit capable of solving the above-mentioned problems and removing noise in the unrecorded area.

(Structure) The present invention provides an optical disc device that irradiates light onto a recording medium and reads out information by receiving the reflected light with a photodetector, which includes a preamplifier, a variable gain amplifier, and variable gain means. A preamplifier amplifies the output signal of the photodetector, and a variable gain amplifier amplifies the output signal of the preamplifier. The gain variable means varies the gain of the variable gain amplifier based on the output signal of the preamplifier during a period in which a valid signal exists.

FIG. 1 shows an embodiment of the invention.

In the optical disc device, light emitted from a laser and reflected by the optical disc is received by a photodetector 21 and photoelectrically converted, and the output signal of this photodetector 21 is amplified by a preamplifier 24 via capacitors 22 and 23. The output signal A of this preamplifier 24 is
As shown in A in the figure, different signals are generated for the ID section, unrecorded section, and data recording section on the optical disc. The output signal A of the preamplifier 24 is an AGC amplifier (variable gain amplifier)
25, and is binarized by a binarization circuit 26 to become read data. Also, the output signal A of the preamplifier 24
is rectified by the full-wave rectifier 27 to become as shown in FIG. 2B, and is binarized by the comparator 28 at a predetermined threshold voltage to become as shown in FIG. 2C. The sampling pulse generation circuit 29 generates a sampling pulse as shown in D in FIG. Sampling and holding is performed at 30, and the result is as shown in E of FIG. Since the gain of the AGC amplifier 25 is controlled by the output signal E of the sampling hold circuit 30, the output signal of the AGCI width amplifier 25 will not be too large in the unrecorded part as shown in F in FIG. Accurate read data can be obtained from the binarization circuit 26 as shown in G in FIG.

The sampling pulse generation circuit 29 is, for example, a monostable multivibrator 31.3 as shown in FIG.
A circuit using 2 is used.

As shown in FIG. 7, the monostable multivibrator 31 is triggered by the rising edge of the output signal C of the comparator 28 to generate a pulse signal of a constant width, and the monostable multivibrator 31 is triggered by the falling edge of this pulse signal.
2 is triggered to generate a constant width pulse signal.

(Effects) As described above, according to the present invention, in an optical disc device that irradiates a recording medium with light and receives the reflected light with a photodetector to read information, a preamplifier that amplifies the output signal of the photodetector; The present invention includes a variable gain amplifier for amplifying the output signal of the preamplifier, and a variable gain means for varying the gain of the variable gain amplifier based on the output signal of the preamplifier during a period in which an effective signal exists. .

Noise in the unrecorded area can be removed, making it possible to read information accurately and stably, and it is also possible to correct variations in the reflectance of the optical disc and decreases in signal amplitude due to changes over time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a timing diagram of the same embodiment, and FIG. 3 is a conventional RF detection/A
FIG. 4 is a block diagram showing the GC circuit, FIG. 4 is a circuit diagram showing the variable impedance element in the circuit, FIG. 5 is a timing diagram of the circuit, FIG. 6 is a block diagram showing the sampling pulse generation circuit of the above embodiment, and FIG. FIG. 7 is a timing diagram of the same sampling pulse generation circuit. 21... Photodetector, 24... Preamplifier,
25... Variable gain amplifier, 27-30... Gain variable means. Dust 2 Mataseintodashide'-9G hV Oral structure 6 Fig.

Claims (1)

[Claims] In an optical disc device that irradiates light onto a recording medium and reads out information by receiving the reflected light with a photodetector, a preamplifier that amplifies the output signal of the photodetector and a variable gain amplifier that amplifies the output signal of the preamplifier are provided. and gain variable means for varying the gain of the variable gain amplifier based on the output signal of the preamplifier during a period in which an effective signal exists.